TISSUE PROTEIN AND ENERGY DEPOSITION IN STEERS FED
DIETS WITH DIFFERENT UREA FERMENTATION POTENTIALS (UFP)

BY

JOSEPH PATRICK TRITSCHLER II

A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

1981

with thee I have lingered once again,

asked and begged and pleaded, cried and wept

for what i have and can not have.

you must think me, an open-hearted fool,

settling for the comfort and confusion in your smile,

so thee i love, before long i die.

thee

innocence
Jeanne
Joseph
andrew
Jeffrey

dying
Jill

ani ta

inqui si t ive
jamey
jan
jane
John
Joanne
robert
susan

independence
david

athletic

o. wi 1 1 iam

James

kathleen dawn
Catherine

di sconcertive

melanie lynn

al ice

kathleen pinckney

paul

Steven

probing
candace
guiomar

cultural

humberto
1 ig ia

art I St ic

clar i ta

pragmatic

el izabeth
maria ines
pol ixsene

commencement
Stacy

ACKNOWLEDGEMENTS
The author would like to express his appreciation to
Ray L. Shirley, chairman of the supervisory comnittee, and to
Joseph E. Bertrand, coordinator of beef cattle research at the
Agricultural Research Center, Jay. Drs. Shirley and Bertrand
were most encouraging, patient and helpful in their guidance of
this endeavor from its inception to culmination. The suggestions
and instructions provided by the members of the supervisory com-
mittee, John F. Easley, Monroe C. Lutrick, Arno Z. Palmer and
Paul H. Smith, are most gratefully appreciated.

Thanks are extended to William 0. Presley, Joseph E. Nelson
and the other employees of the Agricultural Research Center, Jay.
Without their assistance and financial support this project would
not have been possible.

A special debt of gratitude is paid to Joseph M. Harris and
Stacy J. Sloan. Mr. Harris, in his endeavor to meet similar
deadlines, and with his insight, gave a special encouragement.
Ms. Sloan's love and compassion gave the final impetus needed to
attain a long sought goal.

The author wishes to express his appreciation to Ms. Cynthia
Zimmerman for typing this manuscript.

Ml -

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS n i

L I ST OF TABLES v

LIST OF FIGURES vii

ABSTRACT vi i i

CHAPTER

ONE INTRODUCTION 1

TWO L I TERATURE REV I EW k

Energy k

Nitrogen and Energy 16

THREE MATERIALS AND METHODS 39

General 39

Metabol ism Trial A2

Feedlot Trial '»5

FOUR RESULTS AND DISCUSSION 55

Metabolism Trial 55

Feed 1 ot Tr i a 1 62

Empty Body and Carcass 71

Nitrogen to Energy Balance 83

FIVE SUMMARY 92

APPENDIX 96

LITERATURE CITED 100

BIOGRAPHICAL SKETCH 116

- I V -

LIST OF TABLES

Table Page

1. INGREDIENT COMPOSITION OF DIETS TO EVALUATE UFP,

DRY MATTER BAS I S ko

2.. DRY MATTER AND PROXIMATE ANALYSES COMPOSITION OF

DIETS TO EVALUATE UFP i+1

3. EXPERIMENTAL DESIGN OF METABOLISM TRIAL USING STEERS

TO EVALUATE UFP l^^

4. INGREDIENT COMPOSITION OF FEEDLOT ADJUSTMENT RATION,

DRY MATTER BAS I S /|7

5. EXPERIMENTAL DESIGN OF FEEDLOT TRIAL USING STEERS TO
EVALUATE UFP it9

6. DIGESTIBILITIES OF PROXIMATE ANALYSIS CONSTITUENTS AND
TOTAL DIGESTIBLE NUTRIENTS (TON) OF DIETS DESIGNED TO
EVALUATE UFP, DRY MATTER BASIS 56

7. COMPARISON OF CRUDE PROTEIN DIGESTIBILITIES DETERMINED
BY METABOLISM TRIAL AND CALCULATED BY DIGESTIBLE PROTEIN
REGRESS I ON EQUAT I ONS 53

8. METABOLISM TRIAL DATA ON ENERGY UTILIZATION OF DIETS

TO EVALUATE UFP 59

9. METABOLISM TRIAL DATA OBTAINED FOR NITROGEN UTILIZATION

IN DIETS TO EVALUATE UFP 61

10. FEEDLOT PERFORMANCE OF STEERS FED DIETS WITH VARYING

UFP 63

11. STATISTICAL INTERPRETATION OF FEEDLOT PERFORMANCE DATA

FOR DIETS VARYING IN UFP 65

12. ENERGY PARTITIONING DATA OF DIETS VARYING IN UFP 68

13. STATISTICAL INTERPRETATION OF ENERGY PARTITIONING DATA

FOR DIETS VARYING IN UFP 69

^h. EMPTY BODY COMPOSITION AND TISSUE GAINS IN STEERS FED

DIETS VARYING IN UFP 72

15. STATISTICAL INTERPRETATION OF EMPTY BODY DATA FOR DIETS

VARY I NG IN UFP 7Z,

- V -

LIST OF TABLES-CONTINUED

16. CARCASS CHARACTERISTICS OF STEERS FED DIETS VARYING

IN UFP 73

17. STATISTICAL INTERPRETATION OF CARCASS DATA FOR DIETS
VARYING IN UFP 80

18. PREDICTED RUMINAL AMMONIA CONCENTRATION AND UPPER

LIMIT FOR UREA UTILIZATION FOR DIETS VARYING IN UFP 84

19. HETABOLIZABLE PROTEIN (MP) AND UREA FERMENTATION
POTENTIALS FOR DIETS VARYING IN UFP 86

20. COMPARISON OF PROTEIN INTAKE AND PROTEIN TISSUE
DEPOSITION IN STEERS FED DIETS VARYING IN UFP 88

21. COMPARISON OF NET PROTEIN (NP) REQUIREMENTS FOR
PROTEIN TISSUE DEPOSITION IN STEERS FED DIETS

VARYING IN UFP 89

22. DAILY PROTEIN TISSUE GAIN AS A PERCENT OF AVERAGE

DAILY GAIN IN FEEDLOT STEERS 91

23. BODY COMPOSITION DATA OF STEERS IN INITIAL COMPARATIVE
SLAUGHTER GROUP 96

24. COMPARISON OF OBSERVED AND EXPECTED AVERAGE DAILY

GAINS OF STEERS 97

25. CORRELATION COEFFICIENTS BETWEEN VARIABLES OF FEEDLOT
PERFORMANCE, ENERGY PARTITIONING AND DIETARY METABOLI-
ZABLE PROTE IN 98

26. CORRELATION COEFFICIENTS BETWEEN VARIABLES OF DAILY
EMPTY BODY COMPOSITION, CARCASS CHARACTERISTICS AND

D I ETARY METABOL I ZABLE PROTE IN 99

VI -

LIST OF FIGURES

Figure Page

1. General pathways of rumen carbohydrate fermentation 22

2. Relation between ammonia concentration of continuous-

: culture fermentor contents and output of TAPN 29

3. Microbial growth yields in continuous-culture fermen-

tors with purified diets containing urea 30

- V I I

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

TISSUE PROTEIN AND ENERGY DEPOSITION IN STEERS FED
DIETS WITH DIFFERENT UREA FERMENTATION POTENTIALS (UFP)

By

Joseph Patrick Tritschler II

August, 1981

Chairman: Ray L. Shirley

Major Department: Animal Science

A 5 X 5 Latin square metabolism trial and a comparative slaughter

feedlot trial were conducted with 85 British type steers to evaluate

diets with various urea fermentation potentials (UFP). With increasing

dietary nitrogen, UFP values were calculated to be +3.8, +1.2, -l.A,

-3.9 and -6.9 g urea per kg diet. The dietary metabol izable protein

(MP) levels were determined to be 69.2, 76.6, 80. 1 , 8O.8 and 8O.O g

per kg diet, respectively. Crude protein digestibility increased

with decreasing UFP values (P <.005), but TDN, DE and ME showed no

significant relationship to variation in UFP. While NE was not signi-
^ m

ficantly related to UFP, feed efficiency improved and NE increased
logarithmically (P < .05) with decreasing dietary UFP levels. Average
daily gain, DM intake, ME intake and energy balance were parabol Fcal ly
related (P < .005) to dietary UFP levels. Optimal feedlot performance

VI I I

and energy utilization were observed at -1.^ to -3-9 UFP, which
corresponded to maximum dietary MP concentration. Carcass specific
gravity was utilized to determine empty body fat and protein. Daily
gains in empty body weight, fat and energy were parabol ical 1 y related
(P < .001) to dietary UFP levels. Optimal empty body gains were also
observed to occur between -1.4 and -3.9 UFP levels. Empty body pro-
tein gain per day increased logarithmically (?<.05) with decreasing
dietary UFP levels. Carcass characteristics followed similar para-
bolic patterns with changes in dietary UFP. Their respective maxima
and minima suggested that an increased degree of carcass finish
occurred with increased dietary MP concentration. V/h i 1 e the MP
system has merit with respect to predicting animal performance,
it overestimated NP available for protein gained in tissues over

g

the 119-126 day feedlot trial. V;hile predicted NP ranged from I96
to 283 g per day, observed tissue protein gains ranged from 62 to
109. This suggested that only about one third of the predicted NP
was actually deposited in tissues.

CHAPTER ONE
INTRODUCTION

While Florida is a high inventory state in total beef cattle
population, the number of animals finished within the state is
much less than the demands of the consumer. Over 80% of the beef
consumed in Florida is finished out of state. The successful esta-
blishment of an adequate Florida feedlot industry will depend on
development of efficient marketing, slaughter and feedlot facilities.
An efficient feedlot operation is contingent on proper evaluation of
local feed ingredients. Typical feedlot rations are rich in energy
with the proper balance of nitrogen to optimize utilization. While
the grains of Northern Florida are productive, due to lower digesti-
bility they may not have the nutritive quality of nidwestern grains.
Nutrient levels in common feedstuffs given for meeting the require-
ments of beef cattle (NRC, 1976; Church, I98O) may led to underesti-
mation when Florida grown feedstuffs are fed. Studies by Maxson et
a1. (1973) and Brommelsiek et al. (1979) demonstrated that typical
Florida grains do not have the nutrient availability suggested by
comparable feedstuffs listed by the NRC (1971a).

Energy and nitrogen are principle nutrients in feedlot diets.
Understanding the nitrogen to energy relationship is essential for
optimal ration formulation. Microbial fermentation in ruminants,
which precedes mammalian digestion and metabolism, complicates the

- 1 -

nitrogen to energy relationship. Understanding the nitrogen to energy
balance should enhance maximum substitution of dietary non-protein-
nitrogen sources for more expensive natural protein ingredients.
The feedlot industry has accepted the California net energy
system (Lofgreen and Garrett, I968) to predict liveweight gains. How-
ever, net protein as a dietary guideline has been evaluated in a very
limited manner. Burroughs et al. (1975b) proposed the metabol i zable
protein (MP) system to predict the net protein available for maintenance
and production. The quantity of MP available to the animal is a func-
tion of the amount of rumen microbial protein synthesis from ammonia
and energy and the amount of natural protein that resists rumen degra-
dation and bypasses to the abomasum. Under the MP system, corn grain
has approximately 72 g MP per kg when fed to cattle. Corn grain also
has sufficient excess energy for rumen bacteria to generate an addi-
tional 26 g MP, if 12 g urea per kg corn are added to the diet. To
evaluate this addition of non-protein-nitrogen to the diet. Burroughs
et al. (1975b) developed the urea fermentation potential (UFP) . UFP
is expressed as the grams of urea equivalent in terms of excess energy
(positive) or excess nitrogen (negative) per kg dry matter. Positive
UFP values represent dietary energy excesses from which additional MP
may be synthesized if urea or other nitrogen sources are added to the
diet. Burroughs et al. (1975b) determined UFP values for approximately
90 common feedstuffs. UFP values are determined from the total diges-
tible nutrients and crude protein composition of the ration. The MP
system and UFP values have not been evaluated v;ith regard to net pro-
tein tissue gains using feedlot cattle nor with respect to the proper
nitrogen to energy balance using Florida feedstuffs.

- 3

The present study was designed to test the nitrogen to energy

balance in feedlot diets using the UFP and MP system, A metabolism

trial and comparative slaughter feedlot trial v/ere utilized to test

feedlot performance and carcass characteristics for isocaloric rations,

Rations varying in UFP and MP were fed to steers to determine if MP

generated by excess energy plus additional urea could be detected by

increased carcass protein using specific gravity determinations. The

addition of urea to high energy feedlot rations was observed for its

effect on net energies for maintenance (NE ) and gain (NE ). Data

m g

were also obtained for the dietary nitrogen to energy relationship
with regard to feedlot performance, quality of edible meat and empty
body tissue gains.

CHAPTER TWO
LITERATURE REVIEW

Energy
Energy, the principal dietary constituent, generally repre-
sents between 70 and 90^ of the daily dry matter intake. Histori-
cally, energy nutrition and general animal nutrition developed con-
currently. About 1777, the first animal calorimeter was constructed
by the French chemist, Antoine Lavoisier (Maynard and Loosli, I969).
The work of the German physician, Julius Mayer, and the English
brewer, James Joule, led to the formulation of the First Law of
Thermodynamics, that energy is neither created or destroyed. Mayer
reportedly (Moore, 1972) conceived the idea of the conservation of
energy and matter from the observation that oxidation of nutrients
in the animal body produced heat and work. While the proportions of
heat and work might differ for the same quantity of food combusted
in the animal body, their sum should be constant. An alternative
approach, made by the French engineer. Sad i Carnot (Moore, 1972;
Brody, 197^), arrived at the theoretical maximum efficiency of an
ideal engine. Carnot devised a cycle, in complete accordance with
the First Law of Thermodynamics, which gave a precise model for the
conversion of heat into work with the system returning to an iso-
thermal state through a series of reversible steps.

- k

- 5

While the First Law of Thermodynamics could express a theo-
retical maximum efficiency for the conversion of heat into work.
It was obvious that theoretical perpetual motion, consistent with
the principle of conservation of energy and matter, had never been
observed. The subsequent development of the concept of entropy
and its relation to free energy, v;ere directly related to the formu-
lation of the Second Law of Thermodynamics, that there is an energy
loss in the transformation of heat to work. The initial expressions
of the Second Law of Thermodynamics dealt with the impossibility of
constructing the theoretically ideal engine, as described by Carnot
in 1924 (Moore, 1972). Thomson used the Second Law to define a thermo-
dynamic temperature scale (Kelvin). Clausius introduced the concept
of entropy (S) , which gives the directional nature to the physical
and chemical changes that are unaccounted for by the First Law of
Thermodynamics (Lehninger, 1971). Summarizing, the First Law confirms
that, although energy must be conserved, it can be transformed into
work. The Second Law further stipulates that this total energy can
be divided into two fractions, that which is available for work (free
energy) and that which gives direction to physical and biological
processes (entropy).

A consequence of the Laws of Thermodynamics is that the change
in energy in a system is dependent upon the initial and final stages,
independent of the energy path between these states (Brody, 197^;
Moore, 1972). For isothermal conditions, J. Willard Gibbs derived
his classical relation associating free energy (G) , free enthalpy
(H) , and entropy (S) , for a process changing from one state to another

(Moore, 1972):

AG = AH - T A S.
AG [or AF, which is conventionally used for biochemical reactions,
(Lehninger, 1971)] i s the maximal free energy which is theoretically
capable of being transformed into work under conditions of constant
pressure and temperature. AH represents the change in enthalpy or
heat content of the process and is the total energy available for a
biochemical process. T is the constant temperature in degrees Kelvin,
and AS, or change in entropy, is that portion of the total energy
(ah) which directs biochemical processes towards randomness and is
thus unavailable for work.

Brody (197^) and Blaxter (I962) pointed out similarities between
the concepts of thermodynamics and net energy. Since animals are
homeothermic and conform to the Laws of Conservation of Energy and
Matter, then it is not surprising that the concept of net energy
(Armsby, I9IO) adheres to the principle of Gibbs free energy. In
this comparison, metabol izabl e energy (ME) represents the total energy
available to animals. In nutritional terms, ME is analogous to the
AH of biochemical reactions. Given this premise, that portion of the
total energy not convertible to work (TaS) is nutritionally analogous
to heat increment or specific dynamic action (SDA) . Finally, it is
seen that the portion of the total available energy which is capable
of doing work (AG) may nutritionally be considered to be the net
energy (NE) . Thus, the Gibbs free energy equation,

AG = AH - T A S
is seen to be analogous to

- 7

NE = ME - SDA.
This analogue is made with the realization that it is dependent upon
the initial and final states of the process. While these states may
be readily definable for a series of biochemical reactions, the numerous
metabolic processes of even the simpliest organism make it possible
to estimate only the initial and final states. The NE represents
maximum utilizable energy, but no reference is given to level of pro-
duction or to factors which can affect the efficiency of this parti-
tioning.

Rubner (Kriss, 19^3) postulated that the SDA was a composite,
waste energy effect derived from numerous oxidations and side reac-
tions occurring in intermediate metabolism. Since the evolved heat
of biochemical processes is a function of the initial and final states
and is independent of the path between these states, Swift and French
(195^) concluded that the potential energy of ingested food must be
conserved in the potential energies of the excreta, stored body
tissues and heat production. The term heat increment (Hi) has become
synonymous with SDA. However, SDA, as it was originally derived from
Rubner' s theory of isodynamic replacement (Armsby, 1910), refers only
to the heat of nutrient metabolism (HNM). Isodynamic replacement was
probably the first systematic attempt to address the problems of animal
nutrition to the Laws of Thermodynamics. Derived from Rubner's
work with dogs, it postulated, below maintenance, that nutrients
replaced each other in a ration inversely proportional to their ME
values. As Armsby (1910) and later Kromann (1973) pointed out, HI,
as it can be experimentally determined, is a combination of HNM and

- 8 -

the heat of fermentation (HF) . Although, in a true energy scheme, HF
would be considered a digestion loss, it is impossible to experimentally
separate HF from HNM. Thus, the commonly determined HI, as does ME,
contains not only the SDA but the HF, as well.

Even though Armsby (1910) pointed out this discrepancy in Rubner's
isodynamic replacement theory, he continued to determine NE values be-
low maintenance. To Armsby (1917) the NE of a feed or nutrient was a
measure of the feedstuff's ability to diminish the observed energy loss
caused by feeding below maintenance. Developing the first large animal
calorimeter, Armsby and Fries (1915, 1918) derived the first NE feeding
system for cattle. Basically their approach was to determine basal
catabolism and NE values for maintenance by comparing the heat pro-
duction (HP) at two different, sequential submaintenance levels of
intake. This procedure is based on the logic that, above the lower
critical temperature, the consumption of feed increases HP proportional
to intake (Armsby 1910, 1917). Assuming that the animal is above the
lower critical temperature, the HP, in addition to HI, includes the
heat produced in the various metabolic processes necessary to maintain

life. This i s that port ion of the NE required for maintenance (NE ).

m

With this general concept of HP, the NE values of Armsby were based on
the assumption that the utilization of ME was of equal efficiency
(linear) above and below maintenance (Forbes et al., 1927). Earlier,
Forbes et al. (1926a) showed that the computing of HP with above main-
tenance levels of feed intake consistently lead to lower estimates of
fasting catabolism than with submaintenance intake levels. With dairy
cows, Forbes et al. (1926b) demonstrated that the greatest efficiency

9 -

of utilization of feed energy was for maintenance, followed by milk

production and body weight gain, respectively. Instead of proposing

that HP be estimated by extrapolating above maintenance levels of

intake, Forbes et al. (1927) concluded that HP should be estimated

from observed HP during fasting. This HP estimate was less variable

and significantly lower than that determined with above maintenance

feed intake levels. This observation led Forbes et al. (1928) to

conclude that the relation between HP and intake was not linear and

that energy was more efficiently utilized for maintenance than for gain.

This conclusion gave impetus to the division of NE into values

for maintenance (NE ) and for production (NE ). Summarizing the data

m p

of Forbes et al. (1928, 1930) and his own, Marston (19^8) demonstrated
that when HP and available energy intake were reduced by the parameter
of weight in kilograms raised to the 0.73 power (Brody, 197^), the
relation between them was essentially linear for above maintenance
levels of intake. If the relation between HP and ME intake (MEl) is
linear above maintenance and animals conform to the Law of Conservation
of Energy (Blaxter, 1962; Brody, 197^; Kleiber, I96I), then the ob-
servation, that beef cattle have a linear relation between energy gain
and available energy intake above maintenance, is in agreement with
thermodynamic principles (Garrett et al.,1964). Due to these observa-
tions, Lofgreen and Garrett (I968) concluded that NE^ of cattle is
linear and independent of level of feeding above maintenance (Garrett

et al., 1959a, b) .

Below maintenance there is general agreement that HP is not
linearly related to MEl (Armsby, 1910; Forbes et al . , 1928, 1930;

10

Garrett et al., 1959b; Garrett, 1971; Moe et al., 1971, 1972).
Marston (19^8) found this discrepancy consistent with the princi-
ples of thermodynamics. Forbes et al. (1926a) observed that a linear
extrapolation of HP versus intake always resulted in a lower HP
intercept than experimentally determined HP values. Marston (19^8)
postulated that such an extrapolation would represent the animal's
true basal energy requirement, which would be equivalent to the true

NE . The difference between this true basal energy requirement and
m

the observed basal energy requirement would be accounted for by sub-
maintenance catabolism of animal tissue. Accordingly Marston (19^*8)
reasoned that the augmentation of HP, at below maintenance feed in-
take, is due to heat of catabolism of animal tissue and should not
be included in the true basal energy requirement. The distinction,
between using a linear or a curvilinear model to describe the rela-
tion between HP and MEI, is more dependent upon the interpretation
of the definition of maintenance than upon the Interpretation of ex-
perimental results (Flatt et al., 19^5; Moe and Tyrrell, 1973). In
the NE system proposed for dairy cows (NRC, 1971b, 1978; Moe et al.,
1972), the maintenance and production requirement are expressed in
an equivalent linear relation.

Blaxter (1962, I969) developed a ME system in accordance with
the postulation that the efficiency of energy utilization for main-
tenance exceeds that for production with beef cattle (Forbes et al.,
1926b; Kleiber, I96I). In this ME system (ARC, I965), ME has dif-
ferent partial efficiencies for maintenance (K ) and for fattening

m

(K,). The ME for maintenance (ME ) needs are based on fasting meta-

11 -

holism. This is equivalent to using the observed HP for determining

the maintenance requirement. K , the efficiency of ME utilization

for maintenance, is expressed as:

Km = Sh.B + 0.30 Q .

m

Q represents the percent of dietary ME I of the gross energy intake

(GEI) at maintenance. The daily fasting energy expenditure (E) is

calculated from the expression:

E = 0.077 Mcal/W, ^-7^,
kg

Thus, the ME is a measure of the fasting energy required and effi-
m

ciency of ME for maintenance:

ME = E/K .
m m

The efficiency of ME for fattening (K,) is also expressed as a function

K, = 0.81 Q + 3.0.
1 m

From the average daily gain (ADG) , K, and ME , the proportion of ME

for gain per amount of dietary energy can be determined:

Meal ME _ "^f ^^^g^
l<g diet ADG

The NE system for beef cattle, recommended by the NRC (1970,

1976), was presented in its definitive form by Lofgreen and Garrett

(1968). This system has commonly been referred to as the California

net energy system (CNES) , due to the extensive work done at the

University of California at Davis (Garrett et al., 1959b, 196^;

Lofgreen et al., 1962, 1963; Lofgreen, 1965a, b; Lofgreen and Garrett,

1968; Lofgreen and Otagaki, I96O). It was demonstrated by Garrett

et al. (1959b, 1964) and Lofgreen et al. (I963) that the partial effi-

- 12 -

ciency of net energy for body weight gain (NE ) was linearly related
to intake when cattle were fed between maintenance and ad libitum
levels. In the CNES, NE requirement is dependent upon two main factors:
animal size and animal production (or level of intake). Using these
factors, NE is expressed separately as the partial net energy for main-
tenance (NE ) and the partial net energy for gain (NE ) . NE and NE
m 9^9

are expressed separately, because they are more accurate and less vari-
able, particularly with varying levels of intake, than a combined

NE , term,
m+g

The determination of NE and NE involves two experimental phases:

m g

a metabolism trial and a feedlot trial. The metabolism trial is used
to determine metabol i zable energy (ME) by

ME = GE - (energy lost in feces, urine, fermentation).
In practice, these values are obtained using bomb calorimetric values
of the feed (GE) , feces and urine. The energy lost in fermentation,
as CHi gas, is usually estimated from the equation of Bratzler and
Forbes (19'tO);

E = A.012X + 17.68.

_2

In this equation, x represents 10 times the grams of carbohydrate

digested, which yields E grams of methane (CH.) produced. Each gram
of CHi represents a loss of 13.2 kcal.

In a feedlot trial, a comparative slaughter technique (Lofgreen
and Otagaki , I96O) is used to determine the amount of energy accumu-
lated as fat and protein during the feeding period. Lofgreen and

Otagaki (I96O) demonstrated that NE is constant with respect to meta-

m

bolic body weight (W. "' ) and that the fat and protein deposited by

- 13

the animal represents the energy retained for calculation of NE .

g

Reviewing methods of estimating HP, Blaxter (1962) concluded that
the comparative slaughter technique was the only acceptable alter-
native to the costly and laborious methods of direct and indirect
large animal calorimetry.

The accuracy of the comparative slaughter technique is primarily
dependent upon the estimate of carcass composition. While ideally
a complete carcass dissection and composition analysis would be a
definitive measure, the laborious nature of this task places it out
of the realm of practicality. Therefore, alternative carcass com-
position methods have been used. Initially, Lofgreen and Garrett
(1968) utilized equations from Kraybill et a1. (1952) and Reid et al.
(1955) to estimate fat and protein composition by carcass specific
gravity and body water by an antipyrine dilution technique (Garrett
et al., 1959; Whiting et al., I96O). However, serious objections
were raised concerning the accuracy of this technique (Reid and Robb,
1971). In 1969, Garrett and Hinman developed regression equations
from actual chemical determinations of ether extract, water, nitrogen
and energy in the carcass and empty body in relation to carcass
specific gravity. These equations, utilizing carcass specific gravity,
enable the direct estimation of fat (ether extract), protein (nitrogen)
and energy. Although criticism has been raised of the methods used
to estimate empty body composition by the CNES (Reid and Robb, 1971;
Knox and Handley, 1973), it is not imperative to the NE concept that
any particular method be used to estimate composition. Other proce-
dures have also been used. Nankins and Howe (19't6) developed a 9~10-11

1^

rib estimation technique for determining carcass composition. Powell
et al. (1971) proposed the use of multiple regression equations, using
fat thickness over the 12th rib, ribeye area, percent kidney-heart fat
and hot carcass weight, to estimate energy gain. These two techniques
are based on physical separation of the lean and fat in the carcass,
while Garrett and Hinman (I969) actually analyzed the entire carcass
for ether extract and nitrogen and based their equations on this more
sound basis.

Using the comparative slaughter feedlot trial and the metabolism
trial to determine MEI and energy accumulation in the tissue, Lofgreen
and Garrett (I968) have estimated HP from the expression:

HP = MEI - EB.
EB is the energy balance in accordance with the conservation of energy.
If this is compared with the equation:

NE = ME - SDA,

it is seen that at maintenance (EB = O) , HP is equal to MEI, and

MEI = NE + SDA.
m

It is surprising from these concepts, that Lofgreen and Garrett (I968)
arrived at a curvilinear model to express the relation between HP and
MEI. While it is true that the curvilinear model better fits their
data (Garrett et al., 1959b; Lofgreen and Garrett, 1968), this may be
due to the curvilinear nature of the relation between HP and MEI below
maintenance (Armsby, I9IO; Forbes et al., 1928, 1930; Marston, 19^8).
One of the primary criticisms of the CNES is that the slight advantage
in data fit gained by the curvilinear model is unjustified (Knox and
Handley, 1973; Reid and Robb, 1970. Nevertheless, Lofgreen and

15 -

Garrett (1968) chose a curvilinear model to explain the relation

between HP and ME I :

log HP = 1.8851 + 0.00166 MEI.

The HP and MEI are expressed in kcal per kg metabolic body weight

(W. ' ). The value I.885I represents the log HP of a fasting

animal (MEI = 0) and corresponds to a basal HP of 77 kcal/W, ^'^^^

kg

Blaxter (I962) utilized the same basic value for his ME system.

Lofgreen and Garrett (I968) used both maintenance and ad libitum

intake levels from which the basal HP is derived by extrapolation to

zero MEI. This value would represent the HP for the NE and would

m

logically be constant per unit metabolic weight (Marston, ]Sk8) .
Numerous studies have been conducted in which the basal HP fell
within the narrow range of 70 to 82 kcal/W, ' (Brommel siek, 1977;

kg
Harris, I98I; Kleiber, I96I; Knox and Handley, 1973; Lofgreen et

al., 1963; Maxson, 1973; Richter, 1977). The NRC (1970, 1976) has

accepted the value of 77 kcal/W, ' for NE determinations.
^ kg m

The mean daily MEI is determined experimentally by the CNES.
Then from the relation between log HP and MEI, an equilibrium point
is obtained. This is the point where MEI is equal to HP. It is
at this point that energy balance is equal to zero and the value of
ME! represents the energy necessary for maintenance of physical
activity and basal metabolic activity. By means of the ration's ME,
the DM! necessary for energy equilibrium may be determined;

DM! = MEI/ME of ration.

And the NE may be determined for the ration:
m '

NE = 77/DMI.
m

- 16 -

The NE is calculated from the energy retained (EB above maintenance)
9

and the DMI above that which is required for maintenance of energy

equi 1 i br i urn:

NE = EB (above maintenance) .

^ Total DMI - DMI at energy equilibrium

Nitrogen and Energy
Ammonia, amino acids and peptides represent the extracellular
nitrogenous sources available for microbial protein synthesis. Of
these, ammonia is the primary nitrogenous substrate for microbial
cells (Bryant and Robinson, 19^2; Nolan, 1975). Ammonia is of such
importance that in 1963 Hendericks and Martin (Hungate, 1966) ob-
served a correlation between protein solubility and the extent of
protein digestion in the rumen. However, as pointed out by Satter
(1978) and MacGregor et al. (1978), this correlation is misleading
because it suggests that solubility and digestion are synonymous.
Nevertheless, rumen ammonia levels function as an important regu-
lator in the incorporation of dietary nitrogenous sources into
microbial protein (Hungate, I966; Bryant, 1977). In 1963, Bloomfield
et al. observed that some rumen bacteria will utilize ammonia as
the sole nitrogen source, and other strains require ammonia for
growth. Ammonia is the key metabolic intermediate in rumen fer-
mentation through which dietary protein and non-protei n-n i trogen
(NPN) sources serve as microbial nitrogen sources. Stangel (1967)
reported that in the the early igOO's Morgan and coworkers demonstrated
that up to kO% of the dietary protein in sheep could be replaced by
urea. Satisfactory gains by heifers consuming dietary urea supple-

I /

mentation were reported by Hart et al. (1939). In a classical
study, Loosli et al. (19^9) demonstrated that sheep could maintain
a positive nitrogen balance on purified diets containing urea as
the sole nitrogen source. These authors found that all essential
amino acids were synthesized in the rumen of the sheep.

It is well established that ruminants are capable of utilizing
urea as a dietary nitrogenous source. Urea is synthesized from
ammonia in the liver of ureotelic animals via the urea cycle
(Lehninger, 1975). The ammonia arises from the digestive tract
and enters the liver by way of the hepatic portal vein. The urea,
formed in the liver, is either excreted through the renal system,
or recycled to the alimentary canal. Recycling has been shown to
occur either through the rumen epithelium (Houpt, 1959; Houpt and
Houpt, 1968) or in the saliva (Houpt, 1959; Somers, 196la, b, c, d).
Houpt (1959) found that roughly half the urea injected into sheep,
fed a low protein diet, was not recovered in the urine nor found
in other body fluids. It was concluded that the urea served as a
microbial protein source and that urea was recycled primarily through
the rumen wall. Bloomfield et al. (I96)) observed that urea was
readily hydrolyzed by bacterial urease. The urease is found in close
association with the rumen epithelium. The rapid rate of urea hydro-
lysis, to ammonia and carbon dioxide, has been implicated as a major
problem in the efficiency of urea utilization for microbial protein
synthesis (Chalupa, I968). Bloomfield et al . (I96O) found that urea
was hydrolyzed at a rate of 80 mg urea nitrogen per 100 ml rumen fluid
per hour. Under low dietary energy conditions, this could represent

- 18

a four-fold greater rate of ammonia production tiian rate utilization
by rumen microbes. This is consistent with the knowledge that it
is essentially the nitrogen to energy balance in the rumen v;hich con-
trols the growth rate of microorganisms.

The readily hydrolyzable nature of urea may account for its
toxicity problem and its effect on feed intake reduction. Urea
toxicity has been studied by Repp et al. (1955) and Word et al.
(1969). These authors concluded that toxicity generally resulted
from ingestion of large quantities of urea during a short period
to time. Diets which are low in natural protein and high in avail-
able energy, benefit nrrast from urea addition. If the dietary nitrogen
to energy balance is properly considered and unadjusted animals are
gradually adapted to urea over a period of two or three v^(eeks,
then problems with urea toxicity are avoided (Davis and Roberts,
1959). Even if the urea is properly balanced, it has been demon-
strated to have a depressing effect upon feed intake (Bowstead et
al., 19^8; Byers et al., 1955; Loosl i et al., 1958). Van Horn et
al. (1967) observed that as little as 1.9^ urea added to concentrates
depressed the intake of these concentrates in dairy cows. The nitro-
gen to energy balance was not maintained in their urea substitution.

Since ammonia absorbed from the rumen is dependent both upon
its concentration and rumen pH (Bloomfield et al., 1963; Hogan, I96I),
it follows that dietary energy content and frequency of feeding have
important roles in regulating microbial growth rate. Knight and
Owens (1973) observed that slow release of ammonia improved its
utilization. The release of ammonia from urea is dependent upon the

19

quantity of urea in the diet. Caffrey et al. (196?) observed that
the rate of urea hydrolysis was more rapid in rumen fluid from sheep
receiving a diet without urea than in rumen fluid from sheep adapted
to a diet containing urea. These authors concluded that adaptation
to diets containing urea was more a matter of adjustment to urea
ammonia utilization than an adaptation to detrimental effects of
urea.

One of the earliest attempts to quantify the biological value
of protein was the protein efficiency measure proposed by Osborne
et al. (1919). Their protein efficiency value was the body weight
gain per unit of protein intake. Though this measure had some re-
lative merit, it was criticized both practically and theoretically.
Practically, Hegsted and Worcester (19'*7) demonstrated that protein
efficiency was directly correlated to body weight gain and was no
real improvement over body weight gain as an indicatory protein
value. Theoretically, Mitchell (192'*, 19'»3) criticized protein
efficiency evaluation on the basis that the composition of body
weight gain is too highly variable and that no consideration is
given to maintenance protein requirements. When considering diets
of similar composition in rats, Harte et al. (19^8) concluded that
body weight gain was essentially a function of caloric intake.

Bosshardt et al. {]3^S) observed that restriction of caloric
intake resulted in an increased excretion of urinary nitrogen.
Lusk (1923) reported that increasing carbohydrate intake gave a
sparing effect on urinary nitrogen excretion. This effect was pro-
bably due to increased protein nitrogen utilization in the presence

- ?.o

of higher caloric intake. Bosshardt et al. (1946), studying mice
and rats, observed that the level of maximum protein utilization
corresponded to the level of maximum caloric intake per unit body
surface area. These authors observed that, when percentage of
absorbed protein utilized for body gain was plotted against grams
protein absorbed, and when daily calorie intake per gram body
weight rai sed to the two-thi rds power was plotted against grams pro-
tein absorbed, the maxima of both curves occurred at the same
quantity of absorbed protein. Both protein utilization and caloric
intake decreased on either side of the maxima. Sibbald et al. (1956)
postulated, there is an optimal DE level for each nitrogen level of
a ration. These results indicate that there is an optimal nitrogen
to energy balance or that at all levels of protein intake, there is
better growth utilization of protein, if the non-protein caloric
intake is increased.

in ruminant metabolism, the microbial population serves as
a primary source of protein (Purser, 1970). Microbial protein
synthesis requires sources of nitrogen, carbon skeletons, minerals,
vitamins and energy (Hungate, I966). The rumen microbial popula-
tion has the capacity to synthesize the necessary alpha-keto acids
to a large extent from carbon dioxide and to synthesize all its
essential vitamins. The microbial population can utilize ammonia
for its protein nitrogen source (Bryant, 1977).

Rumen anaerobic fermentation of carbohydrates generates chemical
energy in the form of adenosine triphosphate (ATP) upon which the
microorganisms depend for cell synthesis and growth. Baldwin (I965)

21 -

and Hungate (1966) summarized the known metabolic pathways of
rumen carbohydrate fermentation (figure 1). Acetate, propionate,
butyrate, C0„ and CH, are the general end products of rumen micro-
bial fermentation. Stoichiometrically, Hungate (1966) calculated
that from the ratio of end products formed, four to five moles of
ATP per mole of hexose fermented would be expected. Owens and
Isaacson (1977) determined that, dependent upon the proportional
distribution of end products, between 3-6 and 5-6 moles of ATP
v/ould be produced per mole of hexose fermented. While the majority
of these pathways are fairly well established, the mechanisms of
methanogenesJ s and propionatogenesi s have not been completely
determined (Wolin, 1975).

Hungate (I966) suggested that rumen methanogenesi s was a
means of hydrogen disposal, which would increase overall ATP
production. Methanogenesi s permits other substrates to remain
unhydrogenated and thus available for increased ATP production.
Wolin (1975) observed that rumen methanogens exist at an extremely
low partial pressure of H (about 3 x 10 atm.). The low partial
pressure would induce the formation of H , particularly from NADH +
H^. This would in part account for the oxidation of the extensive
quantities of reduced nicotinamide produced during fermentation.
Acetate, H and CO are produced as end products by fermentative
bacteria (Bryant, 1979). The methanogenic bacteria have a very
high affinity for H utilization in methane production (Hungate,
1967; Hungate et al., 1970). Although the mechanism of ATP for-
mation has not been determined for methanogens, analysis has indi-

2?. -

FORMATE

HEXOSE

ATP

PYRUVATE

PXALOACETATE
ATP

ATP

ACETYL-COA

/ \

ACETATE \aTP

BUTYRATE

ACRYLYL-COA

SUCCINATE

PROPIONATE

Figure 1

General pathways of rumen carbohydrate fermentation.
Underscored compounds are those which accumulate as
products. Diagram adapted from Hungate (I966)

23

cated that they have at least three coenzymes unique to the energy
metabolism of methanogenesi s (Bryant, 1979).

The formation of propionate from pyruvate occurs by two
different metabolic pathways. The proportion of propionate formed
by the acrylate pathway, via lactate, increases as the proportion
of readily fermentable carbohydrate increases in the diet. If
feedlot diets are improperly managed, increasing lactic acid pro-
duction can lead to acidosis, founder and laminitis (Church, 1976).

Stoichiometrically, the formation of propionate, via acrylate
instead of succinate, represents an energy loss to microbial
growth. Studying propionate formation by the succinate pathway,
Hobson and Summers (1967) observed higher microbial growth yields
per mole of ATP generated then would have been anticipated from
currently accepted ATP yields. Hobson and Summers (1972) postu-
lated a f lavoprotein- and nicotinamide-1 inked energy transfer
which accounted for the generation of an additional ATP in the
formation of propionate by the succinate pathway. While this
postulate has not been proven, it is consistent with two types
of experimental evidence. The additional ATP appears essential
to the stoichiometric balance, and the reverse reaction, that of
succinate formation from propionate in liver mitochondria, requires
ATP (Flavin et al . , 1955). It should be recognized that these
factors are not conclusive evidence. Frequently biochemical
reactions, which require ATP to proceed in one direction, do not
generate ATP when they proceed in the reverse direction. Also,

- 2k

the initial stoi chiometry was based on the assumption of a specific
upper limitation to microbial growth with respect to energy.

Using Streptococcus faecal is, Bauchop and Elsden (i960)
defined Y as the yield in grams of microbial cell (dry weight)
per mole of ATP and established Y.-j-p to be from 9 to 12. Even
though higher Y.^ values have been observed (Hungate, 19^3;
Hobson and Summers, 19^7), a Y value of 10.5 was concluded
to be the constant which represented the energetic limitation of
microbial growth (Payne, 1970). It was based upon this assumption
that Hobson and Summers (1972) and Hungate et al. (1970 postu-
lated the generation of additional moles of ATP to account for
higher yields of microbial cells than anticipated. However, there
are higher yields which can not be logically explained by postu-
lating greater ATP production (Walker and Nader, 1968; Buchol tz
and Bergen, 1973). Stouthamer and Bettenhaussen (1973) observed
that when Y.^ was measured in an energy limiting chemostat, as
the dilution rate (growth rate) increased, there was a corresponding
augmentation in Y.^ . These authors concluded that there is a
maximum yield of microbial cells obtainable per available ATP.
However, what determines the actual Y. is the proportioning of
the available ATP into energy for maintenance of the microbial
population and into energy for growth. In a steady-state system,
the specific growth rate is equivalent to the dilution rate or turn-
over rate.

Using a mixed rumen culture, Isaacson et al. (1975) and Owens
and Isaacson (1977) observed that with a constant energy supply.

25

as the dilution rate increased, the efficiency of microbial cell
synthesis increased. That portion of the available energy which
contributed to the yield of microbial cells was greater at higher
turnover rates. This was in part due to a more rapid turnover of
the microbial population which led to a smaller population
maintenance requirement. For their mixed rumen culture, Owens and
Isaacson (1977) calculated the theoretical maximal Y to be 19.3,
if all the available energy could be used for growth. Y. in-
creased from 7 at a dilution rate (D) of 0.02 per hour to 17 at
D = 0.12/h.

Thomson et al. (1975) demonstrated that while the total
volatile fatty acid production remains unchanged, as the dilution
rate increases, there is an increase in the molar proportion of
acetate with a corresponding decrease in propionate production.
Wolin (1975) found that increasing the dilution rate shifted
the production of propionate away from the succinate pathway
towards the acrylate pathway for Selenomas ruminantium but no
such shift was observed for Ruminococcus albus.

Cole et al. (1976c) and Kropp et al. (1977a) found that
urea could be substituted, i soni trogenously and Isocalor ically
in the diet of cattle, without any significant effect on microbial
protein synthesis. While there was a tendency to increase micro-
bial protein synthesis with increasing urea substitution, there
was significantly less abomasal nitrogen (P < .01) due to a de-
crease in bypass protein (P < .01) with increasing urea substitu-
tion. The dilution rate tended to increase with increasing urea

- 26 -

substitution. It was concluded that at a constant dilution rate,
urea and soybean meal were i son i trogenousl y interchangeable with
respect to microbial protein synthesis. Soybean meal gave higher
organic matter digestion and nitrogen retention than substituted
urea. The mean ruminal ammonia-nitrogen (NH -N) concentrations
ranged from 12.3 to 13.6 mg per 100 mg rumen fluid. This is well
in excess of the 5 nig per 100 ml necessary for bacterial growth
(Satter and Slyter, 197^). The urea fermentation potentials of
these diets ranged from -40.6 to 6.3 g urea/kg with increasing
percentage of urea substitution from zero to 75% of the supple-
mental soybean meal nitrogen. There were about 10 g microbial
protein synthesized per 100 g DM digested. This value is in
agreement with results by Hume et al. (1970) and Leibholz and
Hartmann (1973). However, this is only about half of the more
generally accepted value, 22 to 23 g microbial protein synthesized
per 100 g OM digested in the rumen (Hogan and Weston, 1970; Miller,
1973; Thomas, 1973).

Several studies (Hungate, I966; Smith, 1975; Bryant, 1977)
have focused on the ability of rumen bacteria to utilize various
nitrogenous sources for protein synthesis. The majority, but
not all, of the bacteria can rely on ammonia as a primary source
of nitrogen. There are relatively little data concerning the pro-
portional importance of NH -N compared to proteins and amino acids
studied in vivo. Nitrogen metabolism in sheep was investigated,
using continuous infusion of N-ammonium sulfate, by Pilgrim et
al. (1970). These authors found N comprised 76-785^ of rumen

- 27 -

bacterial nitrogen {()k-k3% for protozoa) with a low protein diet
(12.5 g N/day) and G2-Sk% for bacteria (4l-35^ for protozoa) with
a high protein diet (22.9 g N/day). The microbes depended upon
ammonia to a minimal extent of 65^ for the low protein diet and
53~55% for the high protein diet. Using a single injection tech-
nique with C-urea, N-urea and N-ammonium sulfate, Nolan
and Leng (1972) found that 71% of the microbial protein was formed
utilizing ammonia with high protein diets (mean = 23.^ g N/day).
Nolan (1975) and Bryant (1977) estimated that between 50 and 70%
of the microbial protein is formed through ammonia as the primary
ni trogen source.

Using a tungstic acid precipitable N measurement, Satter and
Slyter (1972) and Roffler and Satter (1973) demonstrated that,
when ammonia was limiting, the close relationship between microbial
growth and fermentation (Hungate, 1966) did not exist. They showed
that increasing amounts of urea yield a linear increase in microbial
protein synthesis up to a concentration of 5 mg NH -N per 100 ml rumen
fluid, which they estimated to be about 110 g/i<g dietary crude protein
equivalent. Above this level of rumen ammonia concentration, no
further effect was noted. Studies by Orskov et al. (1971, 1972, 197^)
suggested that maximum rumen microbial growth occurred between k and
9 mg NH -N per 100 ml abomasal fluid, equivalent to about 12% dietary
crude protein. Hume et al. (1970) found the point of rumen ammonia
accumulated to be between 8.8 and 13-3 mg NH_-N per 100 ml rumen
fluid. These authors also observed little difference between rumen
and abomasal ammonia concentrations. Although additional work by

28

Satter and Slyter (197^) found actual values of 1.7, 1.9 and 2.0
mg NH^-N per 100 ml rumen fluid, they chose to use the 5 mg per
100 ml value to allow for a small excess. Figure 2 shows the re-
lationship between NH.-N concentration of continuous-culture fer-
mentor contents (dash line) and output of tungstic acid-preci pi tabl e
nitrogen (TAPN) (sol id line) as averages of several diets used by
Satter and Slyter (197^). The crude protein equivalent value cor-
responds to the estimated dietary CP v;hich would give rise to the
corresponding mg NH -N per 100 ml rumen fluid. For cattle the ^CP
and mg NH, -N/100 ml rumen fluid are related to each other by the
equation:

NH -N = 10.57 - 2.5 CP + 0.159 CP^

(Satter and Roffler, 1977). This equation had an r = 0.88. By

2

the addition of ^TPN, the r is raised to 0.92 for the multiple

regression equation:

NH^-N = 38.73-3.0'* CP + 0.171 CP^- 0.^*9 TDN + 0.002^ TDN^.
TON as an energy measure was originally selected by Roffler and
Satter (1975a) for use with dairy cattle diets. When the model
was tested against the data in the literature (Roffler and Satter,
1975b), it was concluded that it would accurately predict growing
and lactating responses to NPN supplementation in dairy cows.
Digestible dry matter (DDM) may be used as an energy measure in-
stead of TDN. Moe et a1. (1972) have established the energy rela-
tionships necessary to convert TDN to DDM.

For the purified diet utilized by Satter and Slyter (1974),
the Y^^ was estimated and is presented graphically (figure 3)

TT

100 -

E
E

X

TO

E

d*

CL.

<

60

20 -

c

0)

c

o —

E
c
<u o

E O

3 —

^- -"v.

O)

c E

60 1i»0 220 300
crude protein equivalent of ration (g/kg)

Figure 2. Relation between ammonia concentration (NH -N) of
continuous-culture fermentor contents (dasn line)
and output of TAPN (solid line). Adapted from
Satter and Slyter (197^).

- 30

I-
<

o

E

o
o
'i

en

16

13

10

<

>-

ko

90

]hO

190

2i»0

crude protein equivalent of ration (g/kg)

Figure 3. Microbial growth yields (Y/i^jp) in continuous-
culture fermentors with purified diets containing
urea. Data from Satter and Sylter (igj't).

- 31

with respect to dietary crude protein equivalent. The TAPN mea-
sured point of ammonia overflow (figure 2) corresponds to the
dietary crude protein level at which Y plateaus (figure 3).
The actual dietary ^CP at which the point of ammonia overflow
occurs would vary with the specific type of diet consumed. Diets
high in energy, containing true protein, with protein resistant
to rumen degradation and which decrease saliva flow, have an in-
creased dietary crude protein level at which ammonia would accumu-
late. Conversely, diets low in energy, high in NPN, containing
easily degradable protein and inducing high saliva flow, would
decrease the dietary crude protein level for the point of ammonia
overflow (Satter, 1978).

Satter and Roffler (1975) have summarized their results on
ammonia accumulation in a practical system for the determination
of nitrogen requirements with respect to energy balance. In this
system, nitrogen and energy are considered the dietary determinants
of the point of ammonia accumulation. Dietary CP and TDN determine
the rumen ammonia concentration, using the multiple regression
equation of Satter and Roffler (1977). NPN may be added to the
diet to the extent that the CP to TDN balance produces up to
5 mg NH--N per 100 ml rumen fluid. Satter and Roffler (1975) ex-
pressed the CP, TDN and NPN relationship in tabular form. Ammonia
accumulation at 5 mg per 100 ml rumen fluid represents the point
of maximal microbial synthesis. Addition of dietary nitrogen,
either CP or NPN, above this level would not contribute to increased
microbial protein synthesis.

Metabol izable protein (MP), as introduced by Burroughs et
al. (1972, 1973a), is the al pha-ami no nitrogen available to the
animal for metabolism. The MP is composed of the microbial pro-
tein plus the dietary CP which bypasses rumen degradation. While
NPN can contribute only to microbial protein (Roffler et al., 1976),
dietary CP, both above and below the point of ammonia overflow,
can also contribute undegraded protein to MP.

The MP concept was originated by Burroughs et al. (1971b),
specifically to deal with the problem of urea addition to cattle
rations. Burroughs et al. (1971c) demonstrated the inaccuracy of
utilizing N times 6.25 to satisfy protein requirements when NPN
feedstuffs are considered in feedlot cattle rations. In order to
overcome the inadequacies of the 6.25 multiplication system, Burroughs
et al. (1971a) introduced the urea fermentation potential (UFP) .
to the MP system. The MP and the metabol i zabl e amino acids(MAA)
are the quantities of digested protein or absorbed amino acids which
are available to the animal for metabolism. This system is the
first attempt to express requirements directly at the tissue level.
MP is the sum of feed protein, which bypasses rumen degradation,
and the microbial protein, which passes from the rumen to the abo-
masum (Burroughs et al., 1972).

The animal's MP requirements were established by a modification
of a method proposed by Mitchell (1929). In this procedure, the main-
tenance needs for net body protein (grams per animal per day) were
derived using the equation of Smuts (1935):

Maintenance = (0.0125) (70.4 W °"^^^).

kg

- 33

The W is empty body weight in l<i log rams. The net protein deposition
in tissues was determined from the data of Haecker (1920), Moulton
et al. (1922) and Fowler (I968). Additional data by Fowler et al.
(1970) and Burroughs et al. (1970a) was in agreement with the pre-
viously obtained protein deposition data. In the Iowa State University
studies, comparative slaughter feedlot trials were conducted using
the 9"10-llth rib procedure of Hankins and Howe (19^6) to estimate
carcass composition. Once the total net protein needs were determined,
the requirement was converted to MP on the basis that 53% of the MP
is lost in metabolism for maintenance and S% is lost in metabolism
for milk production, as established by Virtanen (I966), Oltjen et al.
(1972) and Burroughs et al. (1973b). MAA requirements were established
on the basis of the body amino acid composition data of Block and
Boiling (19'^5), Burroughs et al. (1970b) and the NRC (1964) composi-
tion of meat scraps.

Burroughs et al. (197't) summarized the methods of establishing
MP values for feedstuffs. This procedure involves the determination
of the undegraded dietary protein reaching the abomasum for each
feedstuff. The degraded protein is synthesized into microbial
protein, in the presence of adequate energy, to the extent of
]0.hkZ of the dietary TDN (Pitzen, 197^). The bypass protein
reaching the abomasum was transformed into amino acids using
Morrison (1956) and NRC (1964) data. The amino acid composition
of rumen microorganisms was calculated using data by Meyer et al.
(1967). The MP and MAA were calculated assuming 80% digestion for

- 3^> -

microbial protein (Johnson et al., ]Shh) and 90% digestion for
the undegraded or rumen bypassed feed protein (NRC, 1964).

The estimated MP and MAA requirements were published for
feedlot cattle by Burroughs et al. (1972), Burroughs and Geasler
(1973) and Rouse (1978) and for dairy cows by Burroughs et al.
(1975a, b) . The total MP requirement needed to maintain a
specific ADG decreases slightly with increasing body weight gain
for feedlot steers. Since the maintenance requirement for MP in-
creases with increasing body weight, the amount of MP required per
unit of body weight gain decreases with increasing body weight.
This reflects the differences in carcass composition at different
animal weights. As weight increases, there is a decrease in the
proportion of protein gain with respect to fat gain (Berg and
Butterfield, 1967; Elsley, 1976).

The available MP in a given ration is calculated from the DMi,
the proportion of CP degraded in the rumen, the proportion of CP
bypassing rumen degradation and the TDN of a ration (Burroughs et
al., 1975b).

MP = (P^ X .90) + [(P2 - 15.0) X .80].
The P, in the equation is the grams of bypass alpha-amino protein
per kg feed DM and is considered 90^ digestible. The P represents
the grams of abomasal microbial protein per kg feed DM and is con-
sidered to be Q0% digestible. The number 15.0 represents the amount
of abomasal protein needed to satisfy the metabolic fecal protein
requirement. The P„ factor represents the metabolic balance between
energy and nitrogen. The grams of microbial protein are derived

35 -

from either the grams of dietary CP degraded in the rumen or 10. 't^^
of the grams of TDN per kg feed DM. The P is calculated from the
CP in the case of an energy excess and from the TDN in the case of
a nitrogen excess.

From the amino acid percentages of P, and P ,

MAA = (.9P, X AA%P )/100 + [(.8P - 12.0) x AA^P^l/lOO.

Logically, if the dietary protein, which is degraded and syn-
thesized into microbial protein, passes through an ammonia intei —
mediate, than NPN should be subst i tutable into microbial protein on
an ammonia equivalence basis. For this purpose, the urea fermen-
tation potential (UFP) was introduced by Burroughs et al. (1971a).
UFP reflects the microbial ability to incorporate ammonia, in the
case of sufficient energy, into microbial protein. A positive UFP
value represents the maximal amounts of urea (g/kg feed DM) which
can be fed to obtain maximum formation of microbial protein. The
derivation of UFP assumes that only ^^O percent of the fed urea is
actually converted to microbial protein as,

UFP = (].Ohk TDN - P ) T 2.8.

The P- is the total grams of rumen degraded protein per kg feed DM.

This is the protein which contributes ammonia to the rumen ammonia

pool. The 2.8 factor converts to an equivalent amount of urea. A

positive UFP value times 2.2 gives the grams of microbial protein

synthesized from the additional grams of urea added per kg feed DM.

The 2.2 factor is derived from the grams of MP synthesized from a

kg of urea in the presence of excess energy.

MP = (P, x .90) + [(P, - 15.0) X .80].
urea 1 /

- 36 -

MP = [2800(0) X .90] + ([2800(1.00) - 15.0] X .80).

U lea

MP = 2228 g MP/kg urea,
urea

The MP concept has taken protein beyond the digestibility stage.
MP is the requirement expressed at the level of absorption in the
small intestine after rumen ammonia and digestion losses. The MP
system takes into account microbial synthesis and bypass protein to
express the MP and MAA values of feedstuff s.

The animal requirements are actually determined on a net pro-
tein basis in terms of maintenance protein and tissue protein growth
(or production) requirements. The ef f iciencies of ut i 1 ization of MP
for maintenance and for production have been used to convert animal
net protein requirements to animal MP requirements.

Even with all the adjustments and assumptions accounted for by
the MP system, a net protein (NP) system has been outlined by Fox
et al . (1977) and Fox and Black (1977) to make additional adjustments
not accounted for in the MP system.

The basic NP system (Fox et al., 1977; Bergen et al., 1979) is
structured like the MP system (Burroughs et al., 1975a, b) . The
maintenance net protein (NP ) requirement is also based upon the
equation of Smuts (1935):

NP^ = (0.0125) (70. it W|^ 0-73'+) _
The W is empty body weight in kilograms.

The empty body protein composition (EB ) of the average framed
steer is derived from the equation of Reid (197^+):

EB = 0.235 W - 0.00013 W^ - 2.418.
Adjustments for frame size and sex are made so that animals may be

37 -

compared at a standard composition (Brumgardt, 1972; Ayala, 197'^;
Cr ickenberger et al., 1976b; Klosterman and Parker, 1976). Fox et
al. (1977) have chosen empty body fat at 28.2 to 30.5% as the
standard where steers are expected to grade low choice (Fox and
Black, 1976; Byers et al., 1977).

The animal NP for gain (NP ) requirement is the first derivative
of the Reid (197^) equation, expressed at various average daily gains
(ADG):

NP = (0.235 = 0.00026 W) x ADG.

g

The efficiency of the utilization of MP is assumed to be equal for

maintenance and for gain (Bergen et al., 1978).

The NP values of feedstuffs viere determined by nitrogen balance

trials (Bergen et al., 197^; Fox et al., 1976; Cr ickenberger et al.,

1976a). The protein of feedstuffs is measured as a nitrogen retention

quotient:

rN retained-j
•- N intake ■' '

which can be used to convert CP values to NP values. Only one NP
value for feedstuffs is expressed, since the utilization, for main-
tenance and for gain, is assumed to be at similar efficiencies.

In order to account for the use of NPN supplementation, Bergen
et al. (1978, 1979) developed the ammonia utilization potential (AUP) .
AUP represents the upper limit on microbial protein synthesis:

AUP = Rumen ATP yield x Efficiency of microbial protein synthesis.

AUP - DMI X DE X Rumen OMD x Efficiency of cell yield.
The DMI is the kg of dry matter intake, and DE is the digestible
energy in Meal per kg feed DM. Rumen OMD represents the extent of

30

organic matter digestion in the rumen. The efficiency of cell yield
is the grams of microbial protein synthesized per Meal of rumen DE.
Rumen DE is the DE of the feed times the percent ruminal digestion.
The rumen OMD and the efficiency of cell yield are dependent upon
the dilution rate of the ration. Dilution rates for several types
of rations have been determined by Cole et al. (1976c) and Kropp
et al. (1977b). The efficiency of microbial cell yield, as protein
yield per Meal DE available in the rumen, is determined from the
relationship of dilution rate to microbial cell yield (Cole et al.,
1976c; Kropp et al., 1977b). The extent of rumen OMD is expressed
as apparent rumen OMD as a percent of total apparent OMD. Cole et
al. (1976a, b) and Kropp et al. (1977a) determined the extent of
rumen OMD for several types of rations. If the rumen OMD and the
efficiency of microbial cell yield are known for the ration, than
the AUP can be determined from the DMI and DE content of the ration

In the NP system, NP values for NPN ingredients are determined
comparably to true protein feedstuffs. However, in ration calcula-
tion NPN is only utilizable to the extent that

NPN (NH ) <_ AUP.
The NPN (NH ) is the ammonia derived from NPN ingredients. To the
extent that the NPN (NH ) exceeds the AUP, the NP value of excess
NPN is zero.

CHAPTER THREE
MATERIALS AND METHODS

Genera 1

The experimental design consisted of two trials. A meta-
bolism trial and a comparative slaughter feedlot trial were con-
ducted simultaneously from September, 1979, to February, I98O, at
the Agricultural Research Center of the Institute of Food and
Agricultural Sciences located near Jay, Florida. Eighty-five
yearling steers were randomly selected. Since some of the steers
were purchased at local auction markets, their true ancestry is
unknown. Animals utilized in the study were predominantly Angus,.
Hereford and Angus-Hereford crosses. Through visual examination,
the 85 steers were sorted into three breed groups of 58 Angus,
15 Hereford and 12 Angus-Hereford crosses. Further randomizations
were made from the breed groups into the experimental groups.

All the animals were slowly adapted to corn silage and corn
grain diets during the summer preceding the two trials. Five
Angus steers were selected at random, for the metabolism trial,
and placed in individual feeding stalls, where they were fed the
silage and grain diets. The experimental diets were designed to
be isocaloric but to vary in nitrogen to energy balance utilizing
the urea fermentation potential system (UFP) of Burroughs et al.
(1975a, b) . The ingredient composition and proximate analyses
of the five experimental diets are shown in tables 1 and 2, respec-
tively.

- 39 -

/jO -

TABLE 1. INGREDIENT COMPOSITION OF DIETS TO EVALUATE UFP, DRY MATTER
BASIS

UFP'

b c

I ng redient, % DM Reference no.

+3.8 +1.2 -].k -3.9 -6.9
(+9.8) (+6.9) (+^.3) (+1.2) (-1.8)

Corn grain
Corn si lage
Soybean meal
Urea
Salt^
Limestone

^-02-935
3-08-153
5-0^-60it

6-02-632

64.10 62.7't 62.25 6it.30 66.46

34.76 33.70 32.65 31.40 30.06

2.43 3.87 2.60 1.34

.10 .56 1.01

M .^6 .45 .45 .46

.69 .68 .67 .68 .67

Urea fermentation potential values calculated from data obtained in

present study; values in parenthesis from feedstuffs given by

Burroughs et al. (1975b).

Added 2200 lU Vitamin A per kg diet DM from 16. 8g of Rovimix A-65O

(Roche) .
^ NRC, 1971a.

Contained 281% crude protein equivalent (min).
^ Trace mineralized salt containing 97.0 + 2.0% NaCl, 0.35% Zn, 0.34%

Fe, 0.20% Mn, 0.033% Cu, 0.007% I and 0.005% Co.

Contained 38.8% Ca (min)

- ^1

TABLE 2. DRY MATTER AND PROXIMATE ANALYSES COMPOSITION OF DIETS
TO EVALUATE UFP

Item, %

UFP'

+3.8 +1.2 -1.4 -3.9 -6.9
(+9.8) (+6.9) (+4.3) (+1.2) (-1.8)

Dry matter

Dry matter basis

Ash

Crude fiber

Crude protein

Ether extract

Nitrogen-free extract

58.22 58.85 59.45 60.25 61.12

2.14

2.24

2.30

2.20

2.09

7.06

7.00

6.92

6.70

6.48

9.71 10.62 11.42*^ 12.21^ 13.00^

3.25 3.22 3.19 3.20 3.22
77.84 76.92 76.17 75-69 75.21

Urea fermentation potential values calculated from data obtained in

present study; values in parenthesis from feedstuffs given by Burroughs

et al. (1975b).

Crude protein difference reflects the change in dietary UFP, since

diets were designed to be isocaloric.
*" Includes 0.28% crude protein equivalent from urea.
Includes 1.57% crude protein equivalent from urea.
^ Includes 2.84% crude protein equivalent from urea.

kz -

Metabol i sm Trial

A 5 X 5 Latin square design was utilized for the metabolism
trial. The five diets (table 1) v/ere rotated through the five
periods in the order shown in table 3. The five Angus steers were
halter-broken and housed in individual concrete floor stalls.
Dietary ingredients were weighed using milk scales and mixed by
hand in metal tubs. One of the five steers was removed from the
experiment after the second period, due to refusal of feed when
placed in the elevated metabolism crate. The limited data of this
steer was not included in the statistical analysis.

At the beginning of the first metabolism period, the steers
were implanted with 36 mg zeranol . Each metabolism period consisted
of 21 days divided into three phases: adjustment to the diet,
adjustment to the metabolism crate and fecal and urinary collection
phase. The animals were adjusted for 11 days in stalls with con-
crete floors to the diet fed during that period. The diets were
fed ad libitum to the steers in their individual feeding stalls.
The steers were weighed before being placed into their metabolism
crates and again after being removed. The steers were adjusted
for 3 days to living in elevated metal metabolism crates. Feed
offered in the crates was initially cut to approximately 80^ of
ad libitum level, then adjusted so the animals left a minimal
amount of orts. During the last 7 days of each period, total urine
and feces were collected. Daily samples of feed were taken at the
beginning of the last 7 days of each period. The animals were
fed twice daily, and orts, when present, were collected once daily

^3

TABLE 3. EXPERIMENTAL DESIGN OF METABOLISM TRIAL USING STEERS TO
EVALUATE UFP^

od

Sti

eer no.

Peri

108A

llA

1^2A

129A

121A^

1

-].k

-6.9

+3.8

+ 1.2

-3.9

2

+ 1.2

-3.9

-6.9

+3.8

-\.k

3

-6.9

+ 1.2

-1.4

-3.9

+3.8

A

+3.8

-l.i»

-3.9

-6.9

+1.2

5

-3.9

+3.8

+ 1.2

-]A

-6.9

^ Diets listed by urea fermentation potential values determined in the
present study.

Steer 121A terminated from experiment after period 2; no data from
steer 121A used in analysis of results.

kh

at the time of urine and fecal collection. The steers were given
water in plastic pails twice daily, and their water consumption
was recorded. Two fecal collections vjere obtained daily. The
initial collection was stored in metal trash cans with plastic
liners. Following the second collection, the two collections
were composited, weighed and mixed thoroughly. An aliquot,
representing ]% of the daily fecal material, was stored in
plastic bags and frozen for later analysis. Urine was collected
in plastic bottles covered with two layers of cheese cloth to
minimize contamination. Urine samples were preserved by 10 ml
of toluene and 150 ml HCl (diluted ]:k) added to the bottles
at the beginning of the collection period. Daily the total
urine volume was recorded, and after thorough mixing a 2Z aliquot
was collected in a nalgene bottle and refrigerated for later ana-
lysis. The urine samples were composited from day to day by storage
in the same nalgene bottle. At the end of each period, the feed,
orts and fecal samples were thawed, thoroughly mixed and composite
samples taken. The composite samples were weighed and dried in a
forced-air oven at 60 C for approximately 48 hours. The samples
were then ground to pass through a one mm screen in a Wiley mill.
Proximate analyses were conducted on these samples in accordance
with AGAC (1970) methods. The Parr adiabatic bomb calorimeter was
utilized for gross energy determinations, as described by Anonymous
(i960) and Easley et al. (1965). Urine samples were analyzed for
nitrogen and gross energy following the same procedures. Prior to
calorimetric analysis the urine was dried on solka floe absorbant.

- k5 -

Metabol i zable energy was calculated as the energy in the
feed minus the energy losses in feces, urine and methane of digestion.
Methane energy was estimated from the equation of Bratzler and
Forbes (19^0):

E = k.OMx + 17.68.

In the equation, E is the grams of methane produced, and x re-

-2
presents 10 times the grams of carbohydrate digested. Digested

carbohydrate is the sum of the digested crude fiber and digested
nitrogen-free extract. Each gram of methane produced represents
a loss of 13.2 i<cal of energy.

Digestion coefficients for the various nutrients were deter-
mined as the apparent digestibility by the equation:

DC = Nutrient intake - Nutrient fecal output

Nutrient intake

The data were analyzed statistically using simple regression models
with dietary UFP as a continuous variable and using analysis of
variance comparing treatment effects by the probability of difference
in values by comparing least square means (Steele and Torrie, I96O).
The computer system used the General Linear Models procedure as out-
lined by Barr et al. (1979).

Feedlot Trial
Ten pens with concrete floors and tin roofs covering dirt
areas at one end were used in the feedlot trial. Dicalcium
phosphate (Dynafos), trace mineralized salt and sodium chloride
were provided free choice in each of the feedlot pens. Ten feedlot
groups of eight steers each were randomly selected from the remaining

46

80 steers. Proportional numbers v;ere allocated to each pen from
the various breed groups. One animal from each of the ten feedlot
groups was randomly selected to be an initial slaughter group for
a comparative basis. The ten groups of eight steers were randomly
assigned, two groups per diet, to the five experimental diets. All
steers were fed the adjustment ration, shown in table 4, for two
weeks. At the end of this adjustment period, the steers were fasted
without feed or water for 18 hr prior to being individually weighed.
At this time, the 10 steers selected as the initial slaughter group
were sent to the University of Florida Meats Laboratory in Gainesville.
The remaining 70 animals were each implanted with 36 mg of zeranol
and returned to the ten feedlots, v;here they were fed their respective
experimental diets (tables 1 and 2). The diets were fed twice daily
utilizing a Davis transit mixer-feed v/agon equipped with electronic
scales. The steers were gradually adjusted to their respective diets
by increasing their allotment of fed from day to day until ad libitum
intake was reached in 10 to 14 days. The steers were continued on ad
libitum feed consumption for the duration of the feedlot trial. The
quantity consumed per group per feeding was recorded. All the ingre-
dients, except corn silage and most of the corn grain, were combined
to form a supplement. A small amount of corn grain was added so
that all supplements would constitute the same percent (as fed) of
each diet. At feeding times, the corn silage and remaining corn grain
v;ere weighed directly into the wagon. The supplement was weighed in a
plastic pail using milk scales and added to the bulk ingredients in the
wagon. Diets were thoroughly mixed and weighed out of the wagon

hi

TABLE k. INGREDIENT COMPOSITION OF FEEDLOT ADJUSTMENT RATION,
DRY MATTER BASIS

a b

Ingredient Reference no. DM, %

Corn grain it-02-935 61. ^tS

Corn silage 3-08-153 31.^9

Soybean meal S-Ok-dOk 5.hS

Urea^ - .60

Salt'' - .^0

Limestone^ 6-02-632 .60

^ Added 2200 lU Vitamin A per kg diet DM using 16.8 g of Rovimix A-650

(Roche) .
^ NRC, 1971a.

^ Contained 281^ crude protein equivalent (min).
^ Trace mineral ized salt containing 97.0 + 2.0% NaCl , 0.35% Zn, 0.3'+%

Fe, 0.20% Mn, 0.033% Cu, 0.007% I and 0.005% Co.
^ Contained 38.80% Ca (min).

- AS

into the feed troughs. There were tvio feedlot groups each with seven
animals for each of the five experimental diets. One group, on
each diet, was fed first in the morning, and the other one v;as fed
first in the evening. The diets were fed every day in the same
order, from highest to lowest UFP. One of the two feedlot groups,
fed an experimental diet, was fed for a 119~day period, and the
other group was fed for a 126-day period, as illustrated in table 5.
The feeding period began on October 3, 1979 for all groups. Due to
limited slaughter facilities, half the steers on each dietary treat-
ment were slaughtered one week later than the others.

At the end of their respective feeding periods, the animals were
weighed following an 18 hr fast and shipped to the University of
Florida Meats Laboratory in Gainesville and slaughtered. The initial
comparative slaughter steers and the steers in the ten feedlot groups
were weighed upon their respective arrivals at the Meats Laboratory.
All animals were reweighed the next morning just prior to slaughter.
Empty body weight was determined by manual emptying of the gastro-
intestinal tract and by subtracting the weight of its contents from
the live animal weight just prior to slaughter. Hot carcass weight
was obtained on the kill floor. After cooling for kS hours, the
left sides of the carcasses were evaluated for maturities of the lean
and bone, color of the lean, texture of the lean, firmness of the
lean, color of the fat, marbling in the ribeye, fat thickness over
the 12th rib, ribeye area and percent kidney-heart fat. After evalu-
ation the loin area was removed and frozen for tenderness evaluation
using the Warner Bratzler shear. Dressing percentage (DP) was de-

h3

TABLE 5. EXPERIMENTAL DESIGN OF FEEDLOT TRIAL USING STEERS TO
EVALUATE UFP^

Pen

No. of steers

Days

on feed

Diet, UFP

1

126

+1.2

2

119

+ 1.2

3

119

-].k

ij

119

-6.9

5

126

+3.8

6

126

-1.4

7

119

+3.8

8

119

-3.9

9

126

-3.9

10

126

-6.9 -

^ Diets listed by urea fermentation potential values determined in the
present study; refer to tables 1 and 2 for diet composition.

^ Does not include the 10 steers in the initial comparative slaughter
group.

50

termined by the equation:

DP = Hot carcass weight ,^_

T-. : — 5 :-^rr X 100.

Live animal weight

Overall maturity is the mathematical average of the maturities

of the lean and bone. Quality grade was determined from the overall

maturity and marbling in accordance with the standards set by the

USDA (1975). Yield grade (YG) was calculated from the following

USDA (1975) equation:

YG = 2.50 + (2.50 X fat thickness over 12th rib) +
(0.20 X percent kidney-heart fat) + (0.0038 x
hot carcass weight) - (0.32 x ribeye area).

The right sides of the carcasses were utilized for specific

gravity measurements. Specific gravity was determined on both

sides for the initial comparative slaughter group. However, the

right side was chosen for later specific gravity determinations,

since there was no difference between the left and right sides

for the initial comparative slaughter group. Also, the equations

derived by Garrett and Hinman (19^9) were based on the use of the -

right side of the carcass. Only the right side specific gravity

determinations were used in subsequent comparisons. To determine

specific gravity, the right side of each carcass was weighed in air

and then weighed in water. Both the water and air were at the same

temperature (3^ C) to which the carcasses had been chilled during

the previous kS hours. Specific gravity of the carcass (SGC) was

then determined by the equation:

SGC = Cold carcass weight in air

Cold carcass weight in air - weight in water

51

Using the carcass specific gravity values, carcass and empty body
compositions were calculated from the equations of Garrett and
Hinman (I969).

Carcass ether extract, % = 587.86 - 530.^5 (SGC) .

Carcass water, % = 375.2 (SGC) - 3^*3.8.

Carcass N, % = 20.0 (SGC) - 18.57.

Carcass energy, kcal/g = 49.5'+ - ^3.63 (SGC) .

Empty body ether extract, % = 551-38 - ^98. 5 (SGC).

Empty body water, % = 378. 7^+ (SGC) - 3't5.l8.

Empty body N, ^ = 15-97 (SGC) - 14.17.

Empty body energy, kcal/g = 47-58 - 41.97 (SGC).
The protein compositions were determined by multiplying the percent
N times 6.25-

Lofgreen and Garrett (I968) reported that the kcal daily heat
production (HP) per kg metabolic body weight raised to the three-
fourths power is related to the kcal daily metabol i zable energy in-
take (MEI) per kg metabolic body weight raised to the three-fourths
power by the equation:

Log HP = 1.885 + 0.00166 MEI.
The 1.885 factor is the log of the basal metabolic rate (BMR) as

Log BMR = log (77 kcal/Wj^ °'^^).

The equilibrium point is where the kcal of MEI equals the kcal HP.

This value determines the grams of the specific diet necessary to

maintain the BMR. The ration's net energy for maintenance (NE )

m

in kcal per g is calculated as:

52

NE = 77 kcal/W, ^-^^
m kg

grams of intake at equilibrium point'

The grams of intake at the equilibrium point is the daily dry

matter feed intake, obtained in the feedlot trial, necessary to

give the intake of ME at the equilibrium point.

The net energy for gain (NE ) is measured using the energy

deposition determined from the carcass specific gravity (Garrett

and Hinman, 1969). The NE in kcal per gram of diet is a measure

of the energy retention divided by the diet dry matter intake (DMI)

above maintenance (NE ) as:

m

NE = Energy retained, kcal/\'/, * /day

g \ kg 1

(Total g DMI - g DMI for NE ) /W, °"^^/day

m kg

The total daily DMI is the average daily DMI measured in the feedlot

trial.

The daily fat and protein deposition was determined from the

percent ether extract and percent N (x 6.25) obtained with the

equations of Garrett and Hinman (1969). Using these equations

and the weights of the empty body and the carcass, the total kg of

protein and fat were determined. Using the initial comparative

slaughter group's composition for the determination of initial

empty body and carcass compositions of the steers in the various

dietary treatments, the kg of protein and fat gained with each

diet were calculated. Carcass protein gain (CPG) in kg per day,

for example, was calculated as:

CPG = Carcass protein, kg - Adjusted initial carcass protein, kg

Days on feed

53 -

The adjusted initial carcass protein is the estimated initial
carcass weight and percent protein determined using the initial
comparative slaughter group of steers as a representative sample.
The daily gains of carcass fat and energy and of empty body fat,
energy and protein are derived in the same manner.

Urea fermentation potential (UFP) , metabol izable protein (MP)
and metabol izable amino acids (MAA) were calculated using the formulae
of Burroughs et al. (1975a, b) . These equations are outlined in
the literature review. Estimations of percentages of protein de-
graded in the rumen for the various feedstuffs were taken from the
data of Burroughs et al. (1975a). Comparative UFP, MP and MAA values
were derived using the compositions and values of comparable feedstuffs,
as reported by Burroughs et al. (1975a, b) .

The point of ammonia accumulation was determined using the
equation of Satter and Roffler (1977) with the TDN and CP values
determined in the present metabolism trial. This equation is outlined
in the literature review. Using the tables presented by Roffler
and Satter (1975a) and Satter and Roffler (1975), the upper limit
of NPN utilization was evaluated as the percent dietary crude
protein equal to the point of ammonia accumulation.

Net protein (NP) and ammonia utilization potential (AUP) were
determined using the equations of Fox et al. (1977) and Bergen et
al. (1978, 1979). These methods are outlined in the literature
review.

The data were analyzed statistically using simple regression
models with dietary UFP as a continuous variable. As covariates,

- 5^

initial metabolic body weight and initial animal age were utilized
in an analysis of covariance with UFP. The computer system utilized
the General Linear Models procedure as outlined by Barr et al. (1979)

CHAPTER FOUR
RESULTS AND DISCUSSION

Metabol i sm Trial

The data on digestibilities of proximate analysis constituents
and TDN are presented in table 6. The proximate analyses digesti-
bilities and TDN data were analyzed by linear regression analysis
for significance related to variation in dietary UFP, The digesti-
bilities of organic matter, ether extract and nitrogen-free extract
were not significantly related to dietary UFP levels. Total diges-
tible nutrient values showed no significant relationship with dietary
UFP levels when compared by either linear regression analysis (P=.30)
or least squared means analysis (P=.73). Both the crude protein and
crude fiber digestibilities showed significant linear relationships
to decreasing dietary UFP (P < ,002 and P < .Oh , respectively).
Crude fiber digestibility decreased with decreasing dietary UFP.
The diets had a decrease in the percentage of crude fiber with de-
creasing UFP values (table 2). Much of the overall regression model
significance (P < .002) was contributed by animal and period signi-
ficance (P < .001 and P < .007, respectively). The UFP variable
was only slightly significant (P < .O^*) in the linear regression
model. Crude protein digestibility increased with decreasing dietary
UFP. There was also an increase in the percentage of dietary crude
protein with decreasing UFP values (table 2). Since the diets were

- 55 -

56 -

TABLE 6. DIGESTIBILITIES OF PROXIMATE ANALYSIS CONSTITUENTS AND TOTAL
DIGESTIBLE NUTRIENTS (TON) OF DIETS DESIGNED TO EVALUATE
UFP^, DRY MATTER BASIS

UFP^

! +3.8 +1.2 -1.4 -3.9 -6.9

Item, Z DM (+9-8) (+6.9) (+A.3) (+1.2) (-1.8)

Organic matter GS.h 68.1 68.0 69-9 69.8

Crude fiber-'= 39.8 38.9 37.7 37.6 33-4

Crude protei n-'-'-- 50.9 53.2 53.9 60.5 62.5

Ether extract 64.8 67.3 65.6 64.1 70.4

Nitrogen-free extract 73.4 72.9 72.9 74.6 74.2

TON 69.6 69.3 69.0 71.0 71.2

''• Means are significantly related to UFP by linear regression analysis
(P<.05).

■'■■"•'■' Means are significantly related to UFP by linear regression analysis
(P<.005).

Urea fermentation potential values calculated from data obtained in
present study; values in parenthesis given for feedstuffs by
Burroughs et al. (1975b).

57

isocaloric, an increase in dietary crude protein gives a corresponding
decrease in UFP value, going from a positive UFP (energy excess) to a
negative UFP (nitrogen excess). Protein is considered a nutritive
entity (Lucas and Smart, 1959), because it iias the same true digesti-
bility independent of its percentage in the diet. However, the apparent
crude protein digestibility increases with increasing dietary crude
protein concentration due to the metabolic fecal component which re-
presents a constant proportion of dry matter intake. Data in table 7
demonstrate the similarity between the crude protein digestibility
obtained in the present study and that predicted utilizing the equa-
tions given by Schneider and Flatt (1975) which assume constant true diges-
tibility and constant metabolic fecal component. Although the apparent
crude protein digestibility increased linearly with decreasing dietary
UFP values, in agreement with Schneider and Flatt (1975), the true
crude protein digestibility is probably about 90^ (DM basis) and un-
affected by variation in dietary UFP. Additional linear regression
analyses of crude fiber and crude protein digestibilities related to
a logarithmic transformation of UFP values gave similar, but slightly
less significant results.

The energy utilization data determined in the metabolism trial
are presented in table 8. Gross energy intake increased linearly with
decreasing dietary UFP values (P < .10). Increasing dietary nitrogen
concentration apparently caused a corresponding increase in energy
intake. This increased energy intake probably v^/as related to the in-
creased urinary energy loss. Urinary energy output, both in terms of
Meal per day and percent energy intake, increased linearly with de-

58 -

TABLE 7. COMPARISON OF CRUDE PROTEIN DIGESTIBILITIES DETERMINED BY
METABOLISM TRIAL AND CALCULATED BY DIGESTIBLE PROTEIN
REGRESSION EQUATIONS

Crude protein
digestibi 1 ity, %

Metabol i sm trial

c-i ' .• b
S I 1 age equat i on

Energy feed equation

UFP'

+3.8 +1.2 -1.4 -3.9 -6.9
(+9.8) C+6.9) (+4.3) (+1.2) (-1.8)

50.9
52.0
50.8

53.2
55.3
54.3

53.9
57.8

56.9

60.5
59.9
59.2

62.5
61.8
61.2

Urea fermentation potential values calculated from data obtained in

present study; values in parenthesis from feedstuffs given by

Burroughs et al. (1975b).

Digestible protein = O.908 (crude protein) - 3.77; Schneider and

Flatt (1975) equation for silages.

Digestible protein = O.9I8 (crude protein) - 3.93; Schneider and

Flatt (1975) equation for energy feeds.

- 59 -

TABLE 8. METABOLISM TRIAL DATA ON ENERGY UTILIZATION OF DIETS TO
EVALUATE UFP^

UFP'

I tern

+3.8 +1.2 -1.^ -3.9 -6.9
(+9.8) (+6.9) (+^.3) (+1.2) (-1.8)

Energy intake, Meal /day-
Energy output
Feces, Meal /day
Feces, % intake
Urine, Meal/day"-"
Urine, % in take ''•'^'
Methane, Meal /day
Methane, % intake

2k. \h 25.68 26. Oi* 26.68 26.90

8.16
33.9
1.06
k.l
2.00
8.3

8.90

3^.5
\.\h
k.k
2.06
8.1

8.95
33.9
1.2^*
5.0
2.07
8.0

8.71
32. if
1.^9
5.6
2.15
8.1

8.88
33.0
1.A8
5.2
2.13
8.0

Digestible energy, Mcal/kg DM 2.87 2.86 2.86 2.92 2.91
Metabol izable energy, Mcal/kg DM 2.32 2.31 2.30 2.33 2.33

" Means are significantly related to UFP by linear regression analysis
(P<.10).
"" Means are significantly related to UFP by linear regression analysis

(P< .01 ).
-"•'- Means are significantly related to UFP by linear regression analysis
(P<.005).
^ Urea fermentation potential values calculated from data obtained in
present study; values in parenthesis given for feedstuffs by
Burroughs et al. (1975b).

60 -

creasing dietary UFP values (P < .002 and P < .01, respectively).
Since there was no observed relationship of dietary UFP variation
with fecal and methane energy losses, the increased dietary energy
intake was excreted primarily in the urine. Total urinary excretion
accounted for k.2 to 5.6X of energy intake. Digestible and meta-
bolizable energies showed no significant relationships with dietary
UFP levels when compared by either linear regression analysis (P = .^5
and P = .77, respectively) or least squared means analysis (P = .7^
and P = .71, respectively). Additional linear regression analysis
of feed energy intake and urinary energy output related to a logarithmic
transformation of UFP values gave similar results. While the urinary
energy output results were slightly less significant using the loga-
rithmic transformation, the feed energy intake results were slightly
more significant (R increased from .80 to .81). This slight increase
does not justify the use of the more complex logarithmic regression
model .

The nitrogen utilization data determined in the metabolism trial
are given in table 9. Nitrogen intake increased linearly with de-
creasing dietary UFP values (P <.0002). This is in agreement with
energy utilization data in table 8, which showed increasing energy
intake with decreasing UFP values. Both nitrogen and energy intakes
increased with decreasing UFP values. While increasing the nitrogen
content of isocaloric diets resulted in increased nitrogen and energy
intakes, increased nitrogen and urinary excretions were also observed.
Urinary nitrogen, both in terms of grams per day and percent of nitrogen
intake, increased linearly with decreasing dietary UFP values (P < .0001

- 61

TABLE 9. METABOLISM TRIAL DATA OBTAINED FOR NITROGEN UTILIZATION
IN DIETS TO EVALUATE UFP^

UFP^

A2.5

'♦7.3

50. i*

hl.Z

AS. 7

ks.e

46.5

ks.e

Ao.o

37.5

28.6

3't.6

37.6

52.0

55.0

30.6

33.0

3eA

kk.3

40.2

+3.8 +1.2 -l.it -3.9 -6.9
Item (+9.8) C+6.9) {+h .Z) (+1.2) (-1.8)

N intake, g/day ''"'"'> ZG.k 100.2 IO9.O 120. ^f 128.8

N excretion

Feces, g/day

Feces, % intake-"

Urine, g/day- -•"

Urine, % intake-

N retention, g/day 15.3 18.4 21.1 21.2 25.2

N retention, % intake I8.9 I8.6 19. 8 18.2 20.5

N retention, % absorbed 3^.8 3'*.7 36.0 29.0 J,\ .k

N digestibil ity, ^diet'"--"^ 50.9 53.2 53-9 60.5 62.5

Digested N retained, % diet 36.3 35-5 37.7 30.3 31.3

- Means are significantly related to UFP by linear regression analysis
(P<.01).
-" Means are significantly related to UFP by linear regression analysis

(P<.005).
-"■- Means are significantly related to UFP by linear regression analysis

(P<.001).
^ Urea fermentation potential values calculated from data obtained in
present study; values in parenthesis given for feedstuffs by
Burroughs et al . (1975b) .

- 6:

and P < .006, respectively). The linear decrease (P <.002) in
fecal nitrogen loss, as a percentage of nitrogen intake, with de-
creasing dietary UFP values, is the analogue of increasing nitrogen
(crude protein) digestibilities. This reflects the nutritive entity
relationship between apparent and true digestibilities (table 7).
Although nitrogen retention tended to increase with decreasing UFP
values (P < .08), the significance in the model is due more to
differences between animals (P < .05) than to variation in dietary
UFP (P < .1^). Additional linear regression analysis of nitrogen
intake, nitrogen excretions and nitrogen retention when related to
a logarithmic transformation of UFP values gave similar, but slightly
less significant, results. Although quadratic UFP variables were
not considered due to the experimental design, both nitrogen retention,
as a percent of absorbed N, and digested N retention, as a percent
of dietary N, appear to have optimal values near zero UFP values.
This would imply a maximal efficiency of N retention associated with
a value of zero UFP.

Feedlot Trial

The feedlot performance data of steers fed diets varying in UFP
is shown in table 10. Simple regression analysis was conducted using
UFP values as linear variables (UFP) , as linear and quadratic vari-

ables (UFP + UFP ) and as linear, quadratic and cubic variables (UFP +

2 3
UFP + UFP ). In addition, a simple logarithmic transformation

[in (e - UFP)] of UFP values was analyzed by linear regression analysis.

Those models in which the most complex UFP variable made a significant

63

TABLE 10. FEEDLOT PERFORMANCE OF STEERS FED DIETS WITH VARYING UFP^

UFP^

14

14

14

14

14

318

318

304

310

313

Al6

451

447

449

451

98

133

143

139

138

+3.8 +1.2 -1.4 -3.9 -6.9
Item (+9.8) (+6.9) (+4.3) (+1.2) (-1.8)

No. of steers

Average initial weight, kg

Average final weight, kg

Average gains, kg

Daily dry matter intake, kg-- 7.92 8.66 9.17 9.16 8.90

Average daily gain, kg'«> .80 1.09 1.16 1.13 1.12

Dry matter/ gain'-' 9.86 7.94 7.90 8.15 7-92

" Means are significantly related to a logarithmic transformation of

UFP by linear regression analysis (P<.05); the logarithmic trans-

2
formation used is In (e -UFP).

"" Means are significantly related by simple regression analysis with

linear and quadratic UFP variables (P<.005).

^ Urea fermentation potential values calculated from data obtained

in present study; values in parenthesis given for feedstuffs by

Burroughs et a1 . (1975b).

6k

contribution (P < .10) to the model are summarized in table 11. F
tests were conducted to compare the model error sums of squares (SSE)
for the significance of including quadratic and/or cubic UFP vari-
ables in the model (Cornell, I98I). For example, if the SSE of a
reduced model (i.e UFP) is compared to the SSE of a more complete

model (i.e., ... UFP + UFP ), the significance of the F test is the

2

significance of the additional variable in the model (i.e., ... UFP ).

2

The logarithmic transformation [in (e - UFP)] may not be compared

to the other models by this F test. The prediction error sum of
squares (Press) is used to compare all models for the same parameter
and is a measure of the variation between the observed experimental
values and those values predicted by the model (Gill, 1978). A
lower Press statistic is indicative of less variation and generally

represents a better fit of the model to the experimental data. Co-

2
efficients of determination (R ) and the significance level of the

F tests for each model are also included in table 11. Both dry matter

intake and average daily gain were significantly related by simple

regression analysis with linear and quadratic UFP variables (P < .OO't

and P < .003, respectively). This is indicative that optimal daily

dry matter intake and optimal average daily gain occurred between the

diets with -1.^ and -3.9 UFP values. Feed efficiency (dry matter/gain)

decreased 1 ogari thmi cnl 1 y wi th decreasi ng UFP val ues (P < .02). The

logarithmic model is chosen to represent the relationship between

feed efficiency and UFP, because the linear relationship only tended

to be significant (P < .06), the sequential addition of the quadratic

and cubic variables only tended to be significant (P < .10) and the

65 -

TABLE 11. STATISTICAL INTERPRETATION OF FEEDLOT PERFORMANCE DATA FOR
DIETS VARYING IN UFpe

Regression model

SSE-

Pr>F

Press

Daily dry matter intake
UFP

UFP +

UFP^

In Ce^

■ - UFP)

Average

dai ly gain

UFP

UFP +

2
UFP

In (e^

■ - UFP)

Dry matter/gain

UFP

UFP +

2

UFP

UFP + UFP^ + UFP^

In {e^ - UFP)

i.sr

.56'
1.11

'♦.'45

2.5A
1.36
3. '♦3

ac

cd

ad

00i»

.lik

2.62

004

.79

1.'*'.

01

.59

1.82

.106"

.03

.^♦6

.170

.037^

.003

.81

.06i*

.073

.006

.63

.]]ii

.06

.37

7.30

.03

.6A

5.26

.01

.81

3.78

.02

.52

5.5^*

abed

SSE values for the same parameter with the same superscript are
significantly different (P<.10)'^'*, (P<.05)^, (P<.01)^; analysis
used an F test to compare a reduced model with a complete model
(Cornell, I98I).
^ Feedlot performance data given in table 10; urea fermentation
potential values calculated from data obtained in present study.
Model was not included if additional variable was not significant,
Model error sum of squares.

66

TABLE 11 -CONTINUED
Level of F test significance for model.

Prediction error sun of squares represents a statistical
measure of the variation between observed and predicted
values (Gill, 1978).

67 -

slight reduction in Press statistic value does not justify the use
of the more complex models. There was a significant logarithmic
relationship (P < .02) for feed efficiency to improve with decreasing
UFP values. However, there is still considerable variation (R = .52)
unaccounted for by this logarithmic relation. The combined observa-
tions of dry matter intake, average daily gain and feed efficiency
indicate that optimal feedlot performance occurred at a slightly
negative UFP (-1.^ to -3.9), when determined from TDN, bypass protein
and rumen degraded protein as described by Burroughs et al. (1975b).
This slightly negative UFP range corresponds to the point of maximal
metabol izable protein synthesis.

Using the metabol izable energy values determined in the meta-
bolism trial and the energy gained in the comparative slaughter feedlot
trial, the partitioning of dietary energy intake by feedlot steers
consuming diets varying in UFP is summarized in table 12. ME intake,
energy balance and energy gain are significantly related by simple
regression analysis with linear and quadratic UFP variables (P < .00'*,
P < .0001 and P < .000^, respectively, table 13). Because the diets
are isocaloric ME intake follows the same parabolic pattern observed
for DM intake (table 10). Both energy balance and energy gain indicate
that increased energy deposition occurs with increased energy intake.
The energy balance data was derived by comparing the empty body energy
content after the feedlot trial with the estimated content before the
feeding period using the initial slaughter group data. The energy
content of the empty body was calculated from the equations of Garrett
and Hinman (1969). The energy gain data was calculated from the

TT

TABLE 12. ENERGY PARTITIONING DATA OF DIETS VARYING IN UFP^

UFP^

+3.8 +1.2 -1.it -3.9 -6.9

Item (+9.8) (+6.9) (+'t.3) (+1.2) (-1.8)

ME intake, Meal/day''--^ 18.42 20.00 21.13 21.33 20.79

Energy balance, Meal/day-"* h.jS 6.19 6.66 6.76 6.50

Heat production, Meal/day 13.64 13.81 14.47 14.57 14.29

NE heat,*^ Meal/day 5-96 6.20 6.10 6.18 6.19

m

Heat increment, Meal/day 7.68 7.61 8.37 8.39 8.10

NE , Meal /kg diet DM 1.46 1.45 1.44 1.46 1.46

m

Energy gain, '^ kca1/W|^ '■^^■'^''■'•= 41.26 60. II 65.26 65.82 64.24

NE , Mcal/kg diet DM^- .84 1.11 1.05 1.07 1.11

* Means are significantly related to a logarithmic transformation of

UFP by linear regression analysis (P<.05); the logarithmic transfor-

2

mation used is In (e -UFP).

"" Means are significantly related by simple regression analysis with

linear and quadratic UFP variables (P<.005).
•>"•'• Means are significantly related by simple regression analysis with

linear and quadratic UFP variables (P<.001).

Urea fermentation potential values calculated from data obtained in

present study; values in parenthesis given for feedstuffs by

Burroughs et a1. (1975b).

Energy balance from equations of Garrett and Hinman (1969).

^ NE heat equals 0.077 Meal per W, '^^ .

m ^ kg

Energy gain from equations of Lofgreen and Garrett (I968).

TABLE 13. STATISTICAL INTERPRETATION OF ENERGY PARTITIONING DATA FOR
DIETS VARYING IN UFP^

Regression Model SSE^ Pr>F^ R^ Press^

Metabol Izable energy intake

UFP

UFP + UFP^

In (e^ - UFP)
Energy balance

UFP

UFP + UFP^

In (e^ - UFP)
Energy gain

UFP

UFP + UFP^

In (e^ - UFP)
Net energy for gain

UFP .083 .06 .38 .137

In (e^ - UFP) .068 .02 .^9 -110

7.05^

.02

.50

12.334

3.00^

.OOit

.79

7.761

5.13

.006

.64

8.420

106^

.0001

.33

122

89^

.0001

Ah

105

97

.0001

.39

112

400^

.01

.56

675

95^

.OOOit

.90

183

243

.002

.74

400

^ SSE values for the same parameter with the same superscript are signi

a b

ficantly different (P<.05) , (P<.001) ; analysis used an F test to

compare a reduced model with a complete model (Cornell, I98I).
'' Energy partitioning data given in table 12; urea fermentation poten-
tial values calculated from data obtained in present study.
Model was not included if additional variable was not significant.

- 70 -

TABLE 13-CONTINUED

^ Model error sum of squares.

Level of F test significance for model.

^ Prediction error sum of squares represents a statistical measure
of the variation between observed and predicted values (Gill, 1978)
Energy balance models also contained initial age and initial meta-
bolic body weight as covariates.

71

empty body weight gain using the regression equation of Lofgreen

and Garrett (1963). Optimal energy intake and energy deposition

occurred between -1.^ and -3-9 UFP values. This follows the same

parabolic pattern observed in feedlot performance data (table 10),

with the optimal response occurring near the point of maximal meta-

bolizable protein synthesis. While the NE did not change with
^ ' m

variation in UFP, NE increased in a logarithmic manner with de-
creasing UFP values (P < .02). This indicates that for isocaloric
rations, there is a minimal protein requirement for optimal
energy utilization. The energy deposition data further indicates
that for isocaloric diets, there is an optimal dietary nitrogen
level at which maximal tissue energy deposition occurs. Dietary
nitrogen in excess of this level decreased energy deposition. This
decreased energy gain is due more to a decreased energy intake
(MEI) than to an effect on the efficiency of energy utilization
(NEg).

Empty Body and Carcass
Empty body and carcass data were analyzed following the format
outlined for feedlot performance data. Empty body composition and
tissue gains in steers fed diets varying in UFP are summarized in
table H. From the equations of Garrett and Hinman (1969), the
daily empty body gains in weight, fat, total energy and energy from
protein and fat are significantly (P < .0001) related by simple re-
gression analysis with linear and quadratic UFP variables (tables
13 and 15). The low coefficients of determination (R ) for the

72 -

TABLE ]h. EMPTY BODY COMPOSITION AND TISSUE GAINS IN STEERS FED
DIETS VARYING IN UFP^

UFP^

+3.8 +1.2 -].^ -3.9 -6.9

Empty body item (+9.8) (+6.9) (+^.3) (+1.2) (-1.8)

Average initial weight, kg 281.3 281.2 273-3 276.8 275.3

Average final weight, kg 373-9 ^09.'* A07.0 AI3.5 ^12.3

Daily weight gain, kg-'^''-- .76 1.05 1.09 1.12 1.12

Final percent fat 26.19 27.69 28.88 28.9^ 28.11

Daily fat gain, kg----^'-- .^63 .591 .641 .65O .618

Final percent protein 16.26 15-96 15.73 15.72 15.88

Daily protein gain, kg'- .062 .099 .099 .102 .109

Final energy, Mcal/kg 3.36 3.A9 3.59 3.59 3.52

Dai ly energy gain. Meal-- 4.78 6.19 6.66 6.76 6.50

Daily fat-protein energy gain, 4.69 6.10 6.57 6.66 6.41
Mca 1 -•■ ••-

•'■ Means are significantly related to a logarithmic transformation of

UFP by linear regression analysis (P<.05); the logarithmic transfer

2
mation used is In (e -UFP) .

"" Means are significantly related by simple regression analysis with

linear and quadratic UFP variables (P<.001).

Empty body composition calculated using specific gravity from equa-

73

TABLE 14-CONTINUED
tions of Garrett and Hinman (1969); urea fermentation potential
values calculated from data obtained in present study; values
in parenthesis given for feedstuff s by Burroughs et al. (1975b)
Equivalent to energy balance in tables 12 and 13-

1^

TABLE 15. STATISTICAL INTERPRETATION OF EMPTY BODY DATA FOR DIETS
VARYING IN UFP^

Regression model

sse'

Pr>FJ

r2

Press"^

Dai ly weight ga in

UFP

1.79"'

.0001

.38

2.05

UFP + UFP^

1.37^^

.0001

.53

1.60

UFP + UFP^ + UFP^

1.30"^"

.0001

.55

1.58

In (e^ - UFP)

\.5h

.0001

.^7

1.76

Dai ly fat gai n

UFP

1.18^

.0001

.32

1.37

UFP + UFP^

1.02^

.0001

M

1.22

In (e^ - UFP)

1.10

.0001

.36

1.27

Dai 1 y protein gain

-"

UFP

.0^22^^

.0001

.33

.Ok3

UFP + UFP^

.0386^^

.0001

.39

.0't6

UFP + UFP^ + UFP^

.0365^^

.0001

.42

.OitS

In (e^ - UFP)

.039^

.0001

.38

.0^*5

Daily fat-protein energy

gain

UFP

10i»"

.0001

.33

120

UFP + UFP^

87^

.0001

.Uk

103

In (e^ - UFP)

95

.0001

.38

110

abcdef _.^ , ^

SSE values tor the same parameter with the same superscript are

significantly different (P<.10)'^, (P<.025)^^, (P<.005)^, (P<.001)"^

analysis used an F test to compare a reduced model with a complete

model (Cornell, I98I).

75

TABLE 15-COriTINUED
Empty body data given in table 14; urea fermentation potential
values calculated from data obtained in present study.
Model was not included if additional variable was not significant;
all models also contained initial age and initial metabolic body
weight as covariates.
Model error sum of squares.

Level of F test significance for model.

k

Prediction error sum of squares represents a statistical measure

of the variation between observed and predicted values (Gill, 1978)

7&

empty body data indicate that although empty body data are
very significantly related to variation in UFP, a large portion
of the total variation remains unaccounted for. The regression
models contained initial age and initial metabolic body weight
as covariates to minimize the large amount of animal variation
within the groups. At the initiation of the feedlot trial, steer
weights ranged from 2^0 to 350 kg. Steers of similar breed and
frame score would be at different points on the growth curve
with this variation in initial weight (Berg and Butterfield, 1976).
Initial animal variation was expected to be a major factor affecting
ultimate empty body and carcass composition. Subsequent research
should consider slaughtering animals at the same point on the
growth curve or at the same final composition rather than at the
same point in time. In agreement v/ith the feedlot performance
data (table 10) and the energy partitioning data (table 12), the
empty body composition and tissue gain data indicate that optimal
weight, fat and energy gains occurred with a slightly negative
UFP value (between -1.4 and -3.9). Daily protein gain is loga-
rithmically related to decrees i ng UFP values (P < .0001). This
suggests that there are different protein and fat tissue deposition
responses with respect to optimal nitrogen to energy balance. For
isocaloric diets there is a minimal nitrogen content necessary for
optimal tissue deposition of protein and fat. However, when nitrogen
is in excess, there is a decreased energy (fat) deposition, while
protein tissue deposition remains unchanged or increases slightly.
This decreased adipose tissue deposition is probably due to a de-
creased energy intake (table 12).

- //

The carcass characteristics and their statistical interpretation
are summarized in tables 16 and 17, respectively. The regression
models contained initial age and initial metabolic body weight
as covariates to minimize initial animal variation. Even with the

analysis of covariance, the coefficients of determination (R ) for

2
the carcass characteristics are extremely low. These low R values

suggest that while specific gravity, yield grade, texture of lean,
fat over the ribeye, ribeye area and dressing percentages are signifi-
cantly related to UFP variation, a substantial portion of the overall
data variation still remains unaccounted for. This unaccounted por-
tion may be in part due to the large initial animal variation within
each group, to slaughtering animals at different points in the growth
curve and to the overall difficulty of changing carcass character-
istics by manipulating dietary composition. Berg and Butterfield
(1976) postulated that level of nutrition only affects carcass com-
position indirectly by affecting the rate of growth or the rate of
progression along the growth curve. At the same point on the growth
curve, cattle have comparable carcass characteristics. The effect
of nitrogen to energy balance on carcass character i sti cs could be
better evaluated by slaughtering steers at comparable carcass com-
positions. The evaluation is then in terms of the rate of reaching
a specific carcass composition rather than comparing carcass com-
positions after a specific length of feeding. In these terms, optimal
nitrogen to energy balance is reflected in terms of a greater degree
of finish (fattening) at the end of the feedlot trial. Consistent
with the feedlot performance data (table 10), the energy partitioning

- 78 -

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- 80 -

TABLE 17. STATISTICAL INTERPRETATION OF CARCASS DATA FOR DIETS
VARYING IN UFP"^

Regression model^ SSE Pr>F^ R~ Press

Spec i f i c gravi ty

UFP

UFP + UFP^

0025^^

.047

.14

.00296

00239^

.019

.19

.00287

00248

.025

.16

.00287

In (e^ - UFP)

Yield grade

UFP + UFP^ 54.2 .0001 .33 64.9

In (e^ - UPF) 63.8 .004 .21 74.1

Texture of lean

UFP 24.1^ .14 .10 28.0

UFP + UFP^ 21. 9*" .02 .18 26.4

In (e^ - UFP) 23.4 .06 .I3 27.3

Hot carcass weight

UFP 13977"^ .0001 .76 16166

UFP + UFP^ 9929^ .0001 .83 11646

In (e^ - UFP) 11972 .0001 .80 I3756

Fat over ribeye

UFP + UFP^ 3.53 .0001 .32 4.23

In (e^ - UFP) 4.36 .02 .16 5.10

Ribeye area

UFP 1749 .002 .22 2042

2
In (e - UFP) 1742 .002 .23 2030

81 -

TABLE 17-CONTINUED

Dressing percent
UFP

UFP + UFP^
In (e^ - UFP)

199^

.06

.13

Ilk

187^

.02

.18

11^

195

.03

.U

228

3 be

SSE values for the same parameter with the same superscript are

significantly different (P<.05)^, (P<.025)'', (P<.001)^; analysis

used an F test to compare a reduced model with a complete model

(Cornell, 1931).

Carcass data given in table 16; urea fermentation potential values

calculated from data obtained in present study.

Model was not included if additional variable was not significant;

all models also contained initial age and initial metabolic body

weight as covariates.

Model error sum of squares.

Level of F test significance for model.

Prediction error sum of squares represents a statistical measure

of the variation between observed and predicted values (Gill, 1978)

82 -

data (table 12), and the empty body composition data (table 1^),
the carcass characteristics (table 16) show the greatest degree
of finish (fattening) between the -1.^ and -3.9 UFP diets. Specific
gravity, yield grade, texture of lean, hot carcass weight, fat
over the ribeye and dressing percentages are significantly related
by simple regression analysis to linear and quadratic UFP variables.
These carcass characteristics generally have maximum or minimum
values between the -1.4 and -3.9 UFP diets. Lower specific gravity,
lower yield grade percentages, finer textured lean, heavier carcass
weight, more fat over the ribeye and higher dressing percentages
are consistent with a higher energy intake occurring between the
-1.4 and -3.9 UFP diets. This corresponds to the maximum meta-
bolizable protein content of the diets. Ribeye area increased
(P < .002) with decreasing UFP values. Since the linear and loga-
rithmic models both fit the data equally (table 17), the simpler
linear model was chosen to represent the increasing ribeye area
with increasing dietary nitrogen content. The increased ribeye
area is consistent with the logarithmic increase observed in
empty body protein gain (table 14). While the low R for most
carcass characteristics indicates a substantial amount of vari-
ation remains unaccounted for by the models. The observed changes
in various carcass characteristics is consistent with feedlot
performance and energy partitioning results, suggesting that
optimal carcass finish (fattening) was obtained between -1.4 and
-3.9 UFP values.

83

Nitrogen to Energy Balance
Using the multiple regression equation of Satter and
Roffler (1977), ruminal ammonia concentration was predicted
from the dietary TDN and CP (not including CP from urea).
These predicted ruminal ammonia concentrations and the upper
limit of utilizable crude protein are presented for the diets
in table 18. If natural crude protein is lower than those
calculated from the upper limit values, then urea may be added
as crude protein to mai<e up the difference. Before addition
of urea, the rumen NH -N levels need to be below 5 mg per 100 ml
rumen fluid, which was demonstrated to be the point of ammonia
accumulation by Satter and Slyter (197^). The upper limit of
utilizable crude protein is the maximal crude protein obtainable
by the addition of urea to the diets and is calculated from the
dietary TDN concentration. The dietary crude protein is N
multiplied by 6,25. The upper limit of utilizable crude protein
is the maximum obtainable from the addition of urea. The actual
predicted crude protein is determined by the total dietary crude
protein or the upper limit of utilizable crude protein whichever
value is lower. The predicted dietary crude protein has an optimal
value of about -3.9 UFP. The predicted CP values follow a similar
parabolic pattern observed with the data of feedlot performance,
energy partitioning, empty body energy, fat gain and carcass char-
acteristics indicative of fattening. This suggests that the op-
timal nitrogen to energy balance as predicted by Satter and Roffler
(1977) may serve as an indicator of increased animal performance
and body fat gains due to increased energy intake.

- 8^1 -

TABLE 18. PREDICTED RUMINAL AMMONiA CONCENTRATION AND UPPER LIMIT
FOR UREA UTILIZATION FOR DIETS VARYING IN UFP^

UFP^

i +3.8 +1.2 -1.^ -3.9 -6.9

' tern (+9.8) (+6.9) (+^.3) (+1.2) (-1.8)

Total digestible nutrients, % 69.6

Total crude protein, % 9.7]

Urea, %

NH--N, mg/100 ml rumen fluid 2.85

Upper limit of crude protein, % 11. 35 11.69 11.87 11.82 11. 65

Predicted crude protein,^ % 9.7I 10.62 11.^2 11.82 11.65

69.3

69.0

71.0

71.2

10.62

11.42

12.21

13.00

-

.10

.56

1.01

3.30

3.70

3.06

2.77

Urea fermentation potential values calculated from data obtained in

present study; values in parenthesis given for feedstuffs by Burroughs

et al. (1975b).

NH^-N and upper limit of utilizable crude protein calculated by

equations of Satter and Roffler (1977); NH -N levels do not include

dietary urea NH .

Limited to the lower value of either total dietary crude protein or

the upper limit of utilizable crude protein.

85

Metabol izable protein (MP) v;as calculated using the equations
of Burroughs et al. (1975b). The percentages of corn grain, corn
silage and soybean meal degraded in the rumen, and utilized in the
calculations, were 62, 68 and 75%, respectively, as reported by
Burroughs et al. (1975b). A comparison of MP values calculated
using the TDN and CP values determined in the present study and those
values given for feedstuffs by Burroughs et al. (1975b) is presented
in table 19. Total MP, calculated from TDN and CP values determined
in the present study follow the sane parabolic pattern observed in
feedlot performance and energy retention data. This indicates that
the MP system of Burroughs et al, (1975b) has merit with respect to
predicting animal performance. With isocaloric diets, increasing
MP density resulted in increased dietary dry matter intake. Increased
dietary energy intake resulted in increased animal performance and
increased empty body fat and energy gains. While dietary MP con-
centrations determined in the present study are correlated with in-
creased dietary energy intake, MP concentrations predicted for feed-
stuffs by Burroughs et al. (1975b) continues to increase with de-
creasing dietary UFP values and is not correlated with increasing
dietary energy intake. The primary difference between the feedstuffs
of Burroughs et al. (1975b) and those used in the present study is
the TDN content. The TDN content of feedstuffs of Burroughs et al.
(1975b) are similar to the values used by the NRC (1976), and both
sources tend to overestimate TDN values for comparable Northwest
Florida feedstuffs. Several other digestibility studies, conducted
at the Agricultural Research Center near Jay, Florida (Maxson et
al., 1973; Maxson, 1973; Brommelsiek, 197^, 1977; Brommelsiek et

86

TABLE 19. METABOLIZABLE PROTEIN (MP) AND UREA FERMENTATION POTENTIALS
FOR DIETS VARYING IN UFP^

UFP

I tern, per kg feed DM

+3.8 +1.2 -1.^ -3.9 -6.9

Undegraded abomasal protein (UAP) , g 35-1 37.1 38.2 37.2 36.2

Rumen degraded protein (RDP), g 62.1 69. 1 73.2 69.3 65.^

TDN times .1044,'' g 72.7 72.4 72.0 74.1 74.3

Maximum MP from urea, g - - 2.2 12.5 22.5

Total MP, g 69.2 76.6 80. 1 8O.8 8O.O

Predicted UFP, g

Predicted UAP, g

Predicted RDP, g

Predicted TDN times .1044, g

Maximum MP from urea, g

Predicted MP, g

+9.8 +6.9 +4.3 +1.2 -1.8

33.4 35.7 37-1 35.9 34.8

58.9 66.8 71.5 67.2 62.9

86.3 86.3 86.3 86.2 86.2

2.2 12.5 22.5

65.1 73.6 80.8 86.5 88.2

Urea fermentation potential values calculated from data obtained in

present study.

Tocal digestible nutrients.

Predicted UFP values given for feedstuffs by Burroughs et al., (1975b)

- 87 -

al., 1979), also indicate that energy values from the NRC (1976)

and Burroughs et al. (1975b) are higher than energy values found

for similar feedstuffs grown in Northwestern Florida. This was

especially true for sorghum grain and silage diets.

Protein utilization, in accordance with the MP system (Burroughs

et al., 1975a, b) , was compared with observed protein deposition

in tissues (table 20). MP intake v/as calculated from the feedlot

DM intake (table 10) and the MP content of the diets (table I9).

Net protein (NP) was calculated at klX of MP according to Burroughs

et al. (1975a). The NP for maintenance was estimated from the

equation of Smuts (1935), and the remaining NP was available for

gain. The observed empty body protein gain represents approximately

one third of the expected NP derived from the MP system. While

9

the MP system has a correlation with feedlot performance and energy

retention, it overestimates the NP available for tissue deposition.

9

This overest imation could occur in metabolic fecal values and in
the efficiency of conversion of MP to NP. Chalupa (I98O) and Bull
et al. (1979) reviewed various methods for calculating NP require-
ments and found considerable variation in estimates for both these
areas.

The NP system presented by Fox et al. (1977) predicts lower

NP requirements, using the equation of Reid (197^). These NP
y -^

requirements (table 21) exceed the observed tissue protein gain
by substantial percentages. In general, the systems, which estimate
NP requirements (Chalupa, I98O; Hogan, 1975; Roy et al., 1977;
Fox et al., 1977; Burroughs et al . , 1975 a, b) , overestimate NP

- 88 -

TABLE 20. COMPARISON OF PROTEIN INTAKE AND PROTEIN TISSUE DEPOSITION
IN STEERS FED DIETS VARYING IN UFP^

UFP^

1

1 tern

+3.8
(+9.8)

+ 1.2
(+6.9)

-1.4
(+4.3)

-3.9
(+1.2)

-6.9
(-1.8)

Protein intake, g/day

Crude

769

920

1047

1119

1158

Digestible, true

700

837

953

1018

1054

Digestible, apparent

392

489

565

676

723

Metabol izable

548

664

734

740

713

Net*^

258

312

345

348

335

Net protein utilization, g/day

Maintenance

62

64

64

64

64

Gain (NP )

g

196

247

282

283

271

Protein tissue gain, g/day
Protein gain/NP , %

62
32

99
40

99
35

102
36

109
40

Urea fermentation potential values calculated from data obtained

in present study; values in parentiiesis given for feedstuffs by

Burroughs et a1. (1975b).

Estimated at 9U of CP.

47% of MP (Burroughs et al., 1975a).

From the equation of Smuts (1935).

89

TABLE 21. COMPARISON OF NET PROTEIN (NP) REQUIREMENTS FOR PROTEIN
TISSUE DEPOSITION IN STEERS FED DIETS VARYING IN UFP^

I tern

UFP

+3-8 +1.2 -l.A -3.9 -6.9
(+9.8) (+6.9) (+A.3) (+1.2) (-1.8)

NP requirement, g/day
NP requirement, g/day

62

ek

Gk

6k

Gk

119

158

170

]ek

162

NP, % diet DM
NP, % diet CP

2.9^ 3.27 3.56 3.86 ^.15
30.3 30.8 31.2 31.6 31-9

Dai ly protein gain, g
Tissue gain/NP , %

g

62

99

99

102

109

53

63

58

62

67

^ Urea fermentation potential values calculated from data obtained in
the present study; values in parenthesis given for feedstuffs by

Burroughs et al. (1975b).

From the equation of Smuts (1935).

From the equation of Reid (197'*).

Not considering ammonia utilization potential

- 90

compared to observed protein tissue deposition in the present
feedlot trial. The percentages of daily protein gain with
respect to average daily gain in feedlot steers for a number
of literature references is given in table 22. When DES was
utilized as an implant the percent protein deposition was greater
than when Ralgro or no implant was used. The NP estimates using
the MP system of Burroughs et al. (1975b) predicts more NP avail-

g

able for tissue deposition than was found in the studies cited in
table 22. Estimates of NP are generally determined using short
term nitrogen retention and metabolism studies (Burroughs et al . ,
1973b; Fox et al., 1977; Chalupa, I98O). The use of short
term trials to estimate NP , compared to extended feedlot trials,
appears to overestimate NP availability.

g

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d)

CHAPTER FIVE
SUMMARY

A 5 X 5 Latin square metabolism trial and a comparative

slaughter feedlot trial were conducted with British type steers

to evaluate diets with various urea fermentation potentials

(UFP) for feed efficiency, feed intake, total digestible nutrients

(TDN), digestible energy (DE) , metabol izable energy (ME), nitrogen

utilization, deposition of protein and fat in tissues, net energy

for maintenance (NE ), net energy for gain (NE ) and carcass char-

m g

acteristics. Corn grain and silage diets were fed. V'/ith increasing
dietary nitrogen, UFP values were calculated to be +3-8, +1.2,
-1.^, -3.9 and -6.9 g urea per kg diet dry matter, corresponding
to a crude protein range of 9-7 to 13-0^. The dietary metabol izable
protein (MP) levels were determined to be 69-2, 76.6, 80.I, 8O.8
and 80.0 g per kg diet dry matter, respectively. Crude protein
digestibility increased with decreasing UFP values (P < .005), but
TDN showed no significant relationship to variation in UFP. Dry
matter intake increased (P < .005) with decreasing dietary UFP,
and thereby increased dietary energy and nitrogen intakes (P < .005)
There were corresponding increases (P < .001) in urinary energy
and nitrogen excretions. DE and ME showed no significant relation-
ship with dietary UFP.

92

- 93

Eighty steers were randomly assigned to ten groups of eight

in a comparative slaughter feedlot trial. The five diets with

decreasing UFP were each fed to tvio groups of steers. One steer

from each group was slaughtered at the beginning of the trial to

determine initial body composition. While NE was not siqnifi-

m -^

cantly related to UFP, feed efficiency improved and NE increased

9

logarithmical ly (P <.05)with decreasing dietary UFP levels.
Average daily gain, DM intake, ME intake and energy balance were
parabol ical ly related (P < .005) to dietary UFP levels. Optimal
feedlot performance and energy utilization were observed at -1.^
to -3.9 UFP levels, which corresponds to maximum dietary MP con-
centration.

Carcass specific gravity was utilized to determine empty body
fat and protein. Daily gains in empty body weight, fat and energy
were parabol ical ly related (P < .001) to dietary UFP levels. Op-
timal empty body gains were also observed to occur between -1.^
and -3.9 UFP levels, which corresponds to maximum dietary MP con-
centration. Empty body protein gain per day increased logarithmically
(P < .05) with decreasing dietary UFP levels. Carcass specific
gravity, yield grade, texture of lean, hot carcass weight, fat
over the ribeye and dressing percentage followed similar parabolic
patterns with changes in dietary UFP. Their respective maxima and
minima suggested that an increased degree of carcass finish (fattening)
occurred with increased dietary MP concentration. Ribeye area in-
creased with decreasing dietary UFP levels.

3^

While the MP system (Burroughs et al., 1975b) has merit
with respect to predicting animal performance, it overestimated
NP availability for protein gained in the tissues over the 119

g

to 126 day feedlot trial. The use of short term nitrogen re-
tention studies to establish NP requirements may lead to over-
estimation of NP availability. Further studies should be under-
taken to determine the optimal MP concentration for other dietary
energy levels, to determine NP available for tissue deposition
and to establish specific NP requirements.

APPENDIX

96

TABLE 23. BODY COMPOSITION DATA OF STEERS IN INITIAL COMPARATIVE
SLAUGHTER GROUP

I tern Data

No. of steers 10

Shrunk weight, kg 311.3

Empty body weight, kg 280.1
Carcass specific gravity I.O766

Empty body ether extract, % IA.68

Empty body protein, % 18.88

Empty body energy, Mcal/kg 2.39

97 -

TABLE 2^*. COMPARISON OF OBSERVED AND EXPECTED AVERAGE DAILY GAINS
OF STEERS

I tern, kg per day

UFP

+3.8 +1.2 -].h -3.9 -6.9
(+9.8) (+6.9) (+A.3) (+1.2) (-1.8)

Observed average gain
Expected average gain

.80
.86

1.09
.3^

1.16
1.05

1.13
1.09

1.12
1.03

Urea fermentation potential values calculated from data obtained in
present study; values in parenthesis given for feedstuffs by
Burroughs et al. (1975b).

^Determined from TDN (Church, I98O): TDN = 0.0553 (lb body wt) ' ^
[1 + 0.805Clb gain)].

- 98

TABLE 25. CORRELATION COEFFICIENTS BETWEEN VARIABLES OF FEEDLOT

PERFORMANCE, ENERGY PARTITIONING AND DIETARY METABOLI ZABLE
PROTEIN

Variable

ADG

Feed/gain

MEI

EG^

NE

g

UFP^

MP^

NH^-AP^

DMI 1

.Sh

-.63

1.00

.89

.^9

-.66

.88

.85

ADG

-.95

.83

.97

.8k

-.68

.91

.8k

Feed/gain

-.62

-.90

-.95

.61

-.83

-.Ik

MEI

.88

.h8

-.71

.88

.86

EG

.82

-.75

.96

.90

NE
9

-.62

.77

.86

UFP

-.83

-.91

MP

.97

Energy gain from empty body weight gain by the equation of Lofgreen

and Garrett (1968).

Urea fermentation potential values calculated from data obtained in

present study.

Dietary metabol i zabl e protein content calculated from equations of

Burroughs et al. (1975b).

Maximal dietary crude protein predicted by point of ruminal ammonia

accumulation (Satter and Roffler, 1977).

33

TABLE 26, CORRELATION COEFFICIENTS BETWEEN VARIABLES OF DAILY EMPTY
BODY COMPOSITION, CARCASS CHARACTERISTICS AND DIETARY
METABOLIZABLE PROTEIN

Protein Specific , f u nnS

Variable gain gravity YG^ REA FOE*^ HCW UFP^ MP ^"3"^^

Fat gain .02 -.92 -.50 .27 .hG .70 -.32 .k3 .'♦1

Protein gain .25 -.02 .2k .05 .27 -.hG .52 .kS

Specific gravity .^5 -.07 -.kZ -.kZ .22 -.30 -.29

YG .27 -.82 -.hS .13 -.30 -.27

REA .06 .55 -.15 .lA .11

FOE .k3 -.]k .37 .30

HCW -.25 .33 .31

UFP -.83 -.91

MP , .97

Yield grade percent.
Ribeye area.
Fat over the ribeye.
Hot carcass weight.

Urea fermentation potential values calculated from data obtained in
present study.

Dietary metabol i zable protein content calculated from equations of
Burroughs et a1. (1975b).
^ Maximal dietary crude protein predicted by point of ruminal ammonia
accumulation (Satter and Roffler, 1977).

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12

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BIOGRAPHICAL SKETCH

Joseph Patrick Tritschler II was born May 29, 1950, in
Beaver Falls, Pennsylvania. In June, 1968, he graduated from
Shady Side Academy in Pittsburgh, Pennsylvania. From September,
1968, to January, 1973, he attended Franklin and Marshall College
in Lancaster, Pennsylvania. He majored in theology and psychology
and was awarded his Bachelor of Arts degree on June 3, 1973. From
September, 1973, to December, 197^+, he attended the University of
Wisconsin in Madison, Wisconsin. He majored in biochemistry and
was awarded his Bachelor of Science degree on December 18, 197^.
From June, 1975, to September, 1977, he v;orked as a Peace Corps
Volunteer in Tibaitata, near Bogota, Colombia. He developed analy-
tical techniques and conducted mineral status experiments to in-
vestigate mineral deficiencies and toxicities in grazing cattle and
sheep. While not attending school or working in Colombia, he
either worked as a laborer for Babcock and Wilcox Tubular
Products Division or contracted as a house painter and wallpaper
hanger. Presently, he i s a candidate for the degree of Doctor
of Philosophy in animal science at the University of Florida.

116 -

I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

u

Dr. R.L. Shirley, Chairman
Professor of Animal Seience

I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

Or/. J.E. Bertrand
Professor of Animal Science

J

I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

^■^.Q^

-vi^-^

Dr. A.Z< Palmer
Professor of Animal

Sci ence

I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

^//X^^rCa^

Dr. P.H. Smith
Professor of Microbiology and Cel
Science

I certify that I have read this study and that In my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

/>1 ,^ . c-/// l^^r^

^

Dr. M.C. Lutrick
Professor of Soil Science

I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

•/

^/^i^\

fe^

w/. J.F. Easley /'

Assistant Professor of Animal Science

This dissertation was submitted to the Graduate Faculty of the
College of Agriculture and to the Graduate Council, and was accepted
as partial fulfillment of the requirements for the degree of Doctor
of Phi losophy ,

August, 1981

OU^/l\ <J\ . 6V

Dean, /Col lege of Agricult^/e

/W

Dean for Graduate Studies and
Research

•i

i