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EXPERIMENTAL EVIDENCE OF RESISTANCE

TO HAEMONCHUS CONTORTUS

INFECTION IN SHEEP

By

ANTHONY FRANCIS JILEK

A DISSEBTATION PRESENTED TO T?IE GRADUATE COUNCIL OF

THE UNI\'EKSm- OE FLORIDA

IN P.^RTIAL FULFILLMENT OF TIIE REQUIREMENTS FOR THE

DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA 1968

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation and gratitude to Dr. Marvin Koger^ Chairman of the Super- visory Coiiimittee, for his invaliiahle council and assistance throughout this study and the preparation of this disser- tation. Further appreciation and gratitude are expressed to Dr. a. E. Bradley, Dr. G. T. Edds, Dr. A. C Varnick and Mr. P. E. Loggins, who served as members of the com- mittee, for their valuable suggestions and kind assistance.

The assistance of Mr. Jack Stokes, herdsman of the Sheep Unit, in collection of data, and Mr. Lewis Ergle in analysis of data, is acknowledged with sincere thanks.

The author extends his deepest gratitude to his wife, Anne, for her help in the preparation of this paper and for her encouragement and untiring efforts which made this study possible. Many thanks go to Mrs. Sue Weiss for her effort in typing the rough draft and final copy of this dissertation.

ii

TABLE OF CONTENTS

ACKNOWLEDGMENT^ ii

LliiT OF TABLES iv

INTRODUCTION 1

LITEllVTUilE REVIEW 4

Life Cj'cle and Pathogenesis of Ilaenionchus

contortiis 4

Resistance of Sheep to Ilaemonchus

contortus 5

Immunology 5

Henutology 9

Parasitology 10

Hemoglobin Types of Sheep 11 .■^

>UTERIALS AND METHODS 19

Basic Design and Management Practices. . 19 Resistance of Sheep to Ilaemoncbus

contortus -^z

Iminunology and Hematology 22

Parasitology 24

Hemoglobin Types of Sheep 25

RESULTS 27

Resistance of Sheep to Haemonchus

contortus 27

Immunology and Hematology 28

Parasitology 31

Hemoglobin Types of Sheep 35

DISCUSSION 43

Resistance of Sheep to Haemonchus

contortus 43

Imiiiunology and Hematology 43

Parasitology 44

Hemoglobin Types of Sheep 4C

SU>L^LVRY 50

LITEIUTUilE CITED 52

111

LI:iT OF TABLES

Table Page

^1. Gene Frequency of Hb A in Some Breeds

of Sheep 13

2. Experimental Design: Number of Ewes per

Resistance Group 19

^3. Hemoglobin Type of Sires for 1967 Breeding

Season 22

4. Deviations in the Number of Ewes and Death

Losses by Resistance Group 27

5. Mean Packed Cell Volumes and Hemoglobin

Levels of the Ewe Flock 29

6. Mean Packed Cell Volumes, Hemoglobin Levels

and Total Gamma Globulins of the "Sample Flock" 30

7. Helminth Ova Counts from Ewe Flock .31

8. Helminth Ova Counts and Larval Cultures from

"Sample Flock" 33

.9. Necropsy Haemonchus contortus Counts on Ewes

which Died and Culled Ewes 34

10. Hemoglobin Types of "Sample Flock" by

Resistance Groups 35

11. Hemoglobin Type of Ewe Flock by Resistance

Groups 38

12. Least Squares Analyses for Hemoglobin Level,

Packed Cell Volvune and Body Weight of

Ewes 39

13. Mean Hemoglobin Levels, Packed Cell Volumes

and Weight of the Ewes by Hemoglobin Type

of the Ewes 40

IV

LIST OF TABLES (cont'd)

Table Page

14. The lielationship Between Hemoglobin

Type and Reproductive Perforniance

of Florida Native Ewes 41

15. Least Squares Constants for 70-day

Weight (Pounds) by Type of Birth, Hemoglobin Type of Dam and Lamb ... 42

Figure 1. Starch Gel Showing Hemoglobin

Types Found in Florida Sheep. . 36

IxNTRODUCTION

Internal parasite ir^fections are a major source of econoinic loss to the sheep industry of the world. For example, the U. S. Department of Agriculture (1965) esti- mated annual losses from internal parasite infections in sheep in the United States at approximately 25 million dollars.

According to Soulsby (1965), there has been very little critical study of the economic losses caused by internal parasite infections, but there is ample circum- stantial evidence of the role that Haeinonchus coiilortus plays in causing this loss. It is a ubiquitous parasite, found wherever sheep are raised in the world, and it is the only nematode parasite of sheep that causes a recog- nizable acute disease, haemonchosis. The economic losses are the result of the whole blood constituent losses due to hemorrhage caused by the voracious feeding habits of H. contortus. For example, Martin and Ross (1934) esti- mated blood loss at 30 ml, per day in a sheep with an infection of 2000 H. contortus females, and Clark et al. (1962) calculated that a single adult II. contortus con- sumed 0.05 ml. per day. Therefore, anemia is one of the clinical symptoms regularly associated with II. contortus infections. The degree of anemia is readily estimated by

the determination of the hemoglobin content of the "blood. It has been shown that hemoglobin levels are negatively correlated with the level of H. contortus infection in sheep (Loggins et al., 1965).

The treatment of H. contortus -infected sheep with various anthelmintic drugs is one method currently used in an effort to reduce worm populations and thus prevent economic losses. However, the cost of such dmigs and the labor necessary for administration increases the operating costs of the sheep enterprise. Also, the efficiency of many drugs in reducing the H. contortus levels in sheep may vary and periodic treatments are required. Finally, toxicity of the drugs to the host and the danger of tissue residues is of serious concern in their routine use.

Management practices, such as rotational grazing and dry-lot feeding, have been proposed as methods of controlling H. contortus infections. However, since Cook and Conway (1966) reported that the period from infection with third stage larvae to the onset of ova production was only 14 to 17 days and Ransom (1907) re- ported that ensheathed larvae are very resistant to freezing and drying and thus remain viable for several months, rotational grazing may not be effective. The grazing period would need to be short and the interim period long, resulting in low efficiency of pastures. On the other hand, the mechanical harvesting and trans-

porting of forages to sheep in dry-lot is effective in controlling H. contortus infections^ but involves a large expense and therefore is not commonly used.

Control of H. contortus infections through genetic selection is a method which does not increase operating costs, since genetically resistant sheep would require no special treatment or handling. The existence of a genetic resistance to H. contortus has been suggested by the low H. contortus levels in Florida Native sheep as compared with Rarabouillet sheep in a report by Loggins, Swanson and Koger (1965). The Florida Native sheep is a cross- breed which has developed through natural selection, imder Florida conditions, over the past 300 years.

The objective of this study was to attempt to elu- cidate this apparent genetic resistance to H, contortus infection in the Florida Native sheep, by the use of certain laboratory techniques. In addition to hemato- logical, immunological and parasitological measurements, production data on the experimental sheep flock was collected. Finally, all data was subjected to statistical analysis to determine the significance of the results.

LITEIUTUHE REVIEW Life Cycle and Pathogenesis of Haemonchus contortus

The nematode H. contortus is a parasite of sheep which normally inhabits the abomasvim. The life cycle of H. contortus was first worked out by Ransom in 1906 who reported that the ova which were passed in the feces, became embryonated and hatched within 14 to 19 hours, under suitable conditions of heat and moisture, releasing first stage larvae. The larvae are quite active and feed for 10 to 12 hours at which time they moult into the second stage, which is also an active, free-living, feeding stage. About three days after hatching, the larvae moult into the third, or infective, stage which migrates up blades of grass and are thus available for ingestion by grazing sheep.

Upon ingestion, a dialyzable factor, or factors, present in the sheep rumen stimulates the release of "exsheathing fluid" from a region near the excretory cell of the larvae which enables the larvae to break out of the sheath (Soramerville, 1957). The larvae pass to the abomasum and undergo two additional moults reaching the sexually differentiated young adult stage (Silverman and Patterson, 1960). Cook and Conway (1966) found that the period from infection by the third stage infective larvae until onset of reproduction as an adult H. contortus

4

varied from fourteen to seventeen days,

Boughton and Hardy (1935) observed that the parasites attached themselves to the stomach wall "by a peculiar striking motion of the head and neck, and that they re- mained attached for about twelve minutes. The parasites detached themselves from the stomach wall leaving minute hemorrhages which continued for a maximum of seven minutes. Andrews (1942) reported that blood appeared in the feces six to ten days after sheep were given H. contortus in- fective larvae. Fourie (1931) concluded that the anemia observed in sheep experimentally infected with H_j_ con- tortus was purely hemorrhagic in character, since he was able to reproduce the same blood picture in healthy lambs by periodic bleeding from the jugular vein.

Resistance of Sheep to Haemonchus contortus

Immunology

Reports on resistance to parasitic nematode infections support the view that an immune response, probably humoral in nature, is stimulated by the excretions and/or secre- tions of the invading parasites (Taliaferro, 1940; Campbell, 1955; and Chipman, 1957).

Stoll (1929) first reported on a "self -cure" phenomenon in sheep with expulsion of H. contortus and protection of the animals thereafter against any significant amount of further infection. In his experiment, one of the two worm- free lambs was given 45 infective H. contortus larvae by mouth. Both lambs were then maintained on the same small

pasture, with the infective lamb serving as the source of natural infection for the other and for repeated in- fection of itself. An initial build up of an infection as measured by ova counts in the feces and hemoglobin levels was followed by expulsion of adult H. contortus and protection of the lambs against natural and challenge reinfections with H, contortus infective larvae.

Gordon observed that "self -cure" was usually seen when there was a fresh growth of pasture, along with an in- creased H. contortus larval intake, but was of short dur- ation and often insufficient to promote a rapid increase in body weight. . oheep which had expelled an infection of n. contortus were not always resistant to later rein- fection. A sheep which underwent "self -cure" on one oc- casion may have succumbed to haemonchosis when the next outbreak occurred a few weeks later.

Stewart (1950b) found that the intake of large doses of infective larvae of H. contortus was the exciting cause of the "self -cure" phenomenon. Stewart (1953) concluded that "self -cure" did not result in a release of hetero- logous antibodies into the blood stream of the sheep. There was a reaction of the host associated with allergic sensitization and an edeinatous condition of the mucous membrane of the abomasum of the host after the adminis- tration of larvae. The abomasum of lambs which had not been exposed to H. contortus larvae previously reiiuined flaccid and normal when massive doses of exsheathed larvae

were injected into the abomasiini (Stewart, 1955). In lambs hypersensitized by previous infections with II. contortus . the aboraasura showed increased peristalsis and segmentation within ten minutes of the injection of the massive doses of the exsheathed larvae. Within one hour, the abomasum was pale, edematous and had contracted in diameter. The reaction of sheep resistant to H. contortus was similar to that of the previously infected sheep.

Soulsby et al. (1959) found that at the time of the "self -cure" phenomenon, the majority of the existing adult H. contortus population was in the small intestine and in a state of disintegration, although third and fourth stage larvae of varied sizes were present in the abomasum. This finding supports the evidence presented by Soulsby and Stewart (1960) that the main antigenic stimulation of the "self -cure" phenomenon was derived from substances released by larvae during the third moult.

The rate of development of the parasitic phase of H. contortus is dependent upon the age and immunological state of the host. Gordon (1948) observed that adult animals were generally more resistant but, in the field, it usixally was not possible to separate the effects of age from those of a previous infection. The differen- tiation and development of larvae was more rapid in sus- ceptible lambs than in older susceptible sheep (Silverman and Patterson, 1960). In their report the differentiation and development of larvae in resistant sheep became inhibited

at the fourth and fifth stages and were expelled from the sheep .

Studies on the host-parasite relationship of H. contortus suggested that important antigens were released during growth and development of the parasite as it penetrates, moults and matures in the host (Silverman, 1965) . No evidence of host tissue responses to the larvae in either susceptible or resistant sheep was observed up to the ninth day after infection (Silverman and Patterson, 1960). Damage to host tissue first oc- curred after the tenth day when young adults began to burrow into the mucosa. Fourth and fifth stage larvae showed the greatest antigenic activity and were the most susceptible to the adverse effects of serum from resis- tant animals, in vitro, while neither third stage larvae nor adult worms showed any apparent reaction to such serum (Silverman, 1965).

Several methods to elicit resistance in sheep to H. contortus are reported in the literature. Severe anemia and death following challange doses of infective larvae were prevented by previous infection with imma- ture stages of H. contortus (Stoll, 1942; Christie et al« . 1964 a; Christie et al., 1964b and Dineen et al., 1965). Stewart (1950 a) reported that ground, mature H. contortus. ground infective larvae, and heat-killed larvae did not stimulate detectable antibody responses. Jarrett et al.

(1959, 1961) showed that vaccination with irradiated larvae produced a resistance sufficient to withstand large

challenge doses of infective larvae.

Experimental bleeding (Bemrick et al., 1958) and mineral supplementation (Veir et al., 1948; Richard et al. . 1954 a; and Richard et al., 1954 t> ) appeared to increase resistance of lambs to H. contortus infections. Emerick et al. (1957) postulated that supplementation of the ration with cobalt increased the synthesis of vitamin B-,2 in the rumen in response to the severe drain of blood by H. contortus. Heinatology

Anemia is one of the clinical symptoms associated with haemonchosis in sheep. Georgi and ^Vhitlock (1967) reported a positive correlation between exposure to H. contortus infection and onset of erythrocyte loss in sheep, supporting the assumption that blood loss leading to anemia was caused by H. contortus.

Bemrick et al. (1958) concluded that one of the most important factors in the development of a resistance to challenge infections with H. contortus in lambs was the hemorrhage produced by the blood sucking habits of the worms. Shutt and McDonald (1965) reported that experi- mental anemia, maintained by daily bleeding, provoked a marked increase in the rate of hemoglobin synthesis, about 3^ times the normal rate.

Loggins et al, (1960) found that hemoglobin levels in sheep varied significantly between breeds. Holman (1944) and Becker and Smith (1950) observed no significant differences between breeds of sheep with regard to blood

10

constituents studied. However, Loggins et al, (1965) reported breed differences in II, contortus ova counts and adult H. contortus counts at necropsy. These latter results suggest that the breed differences in hemoglobin levels may be confounded with the degree of resistance to H. contortus infections. For example, Florida Native sheep had higher hemoglobin levels and lower H. contortus ova counts and worm counts at necropsy than Ramboiiillet sheep. Parasitology

Christie et al. (1964 c) presented ova count data which suggested that host rv^sistance involved a resistance to the establishment of H. contortus. Suppression of ova production per H. contortus female had not occurred, and retardation of development of larvae was the major effect of control on the parasitic burden (Dineen et al., 1965). However, Kingsbury (1965) reported that counts of helminth ova in the feces of an infected animal was not a reliable measure of the level of infection. Counts ranged from 500 to 2000 ova per gram of feces regardless of the actual population of sexually mature worms in sheep with some large populations yielding counts of less than 1000 ova per gram of feces.

Christie and Brambell (1966) observed significantly lower worm populatLons in lambs protected by previous H. contortus infections than ixi uninfected controls fol- lowing a challange dose of H. contortus infective larvae. Loggins et al. (1965) reported lower worm counts in Florida

11

Native sheep than in RamlDouillet sheep. No significant relationship was found between the degree of infection at the time "self -cure" occurred and the degree of re- duction in worm burden resulting from "self -cure" (Gordon, 1948). "Self -cure" operated to some extent in all the sheep, irrespective of their worm burden.

Hemoglobin Types of Sheep

Hemoglobin, a complex molecule, consisting of iron, a porphyrin ring and globin, has been studied for more than 30 years (Kitchen, 1965). Hemoglobin differences reside in the protein moiety (globin) which comprises 95 percent of the hemoglobin. The globin of hemoglobin consists of two pairs of polypeptide chains which form a tetraraer. In adult sheep hemoglobins, the polypeptide chains pairs are designated the alpha and beta chains. The two beta chains are replaced by two gamma chains in fetal hemoglobin. The abbreviation "Hb" will be used in this report to designate specific hemoglobin types.

The heterogeneity of types of sheep hemoglobins has been well established. Harris and Warren (1955) found three electrophoretically distinguishable types in a group of ewes: a) a single relatively fast-moving hemoglobin, b) a single relatively slow-moving hemoglobin, and o) both the relatively fast-and relatively slow-moving hemo- globins. Evans et al. (1956) designated the three hemo- globin types as Hb A, Hb B and Hb AB, respectively. Helm et al, (1957) described two hemoglobins in Dutch sheep>

12

the faster-moving hemoglobin which they designated as Hb II and the slower-moving hemoglobin which they desig- nated as Hb I. Although no direct comparison was made, the two hemoglobins appeared similar to Hb A and Hb B, respectively.

Preliminary evidence has indicated that these types are genetically determined in a simple Mendelian manner (Evans et al., 1956). The genes for the two hemoglobins (Hb A and Hb B) in sheep are allelic and they are co- dominant. This type of inheritance was also shown by Huisman et al. (1958). In sheep heterozygous for Hb A and Hb B both hemoglobin types were equally distributed among all red blood cells (Woore et al., 1966).

Breed differences in gene frequencies of Hb A have been reported by several authors and are summarized in Table 1. The frequency of Hb A ranged from 0.99 in the Norwegian Spael to 0.01 in the English Leicester. Evans et al. (1957) reported that gene frequencies in different flocks of the same breed were in good agreement. In general, the lowland breeds of British sheep were predom- inantly of Hb B, while Hb A was more conspicuous in the mountain and hill breeds, possibly indicating that the hemoglobin type may be of some adaptive significance. This theory was supported by differences in gene frequency in the Romney Marsh breed under the different environmental conditions of Great Britain and Australia (Evans and Blunt, 1961). Similar differences were observed when gene frequencies in the Down or Shortwool breeds from Great

13

Breed

TABLE 1

Gene Preq.uency of H"b A in Some Breeds of Sheep

Gene

Location

Frequency

of

of Hb A

Flock

Reference

Scottish Blackface

North

Country

Cheviot

South Devon

English Leicester

Merino

Ramhouillet

Spa el

Cheviot

.77

.43

.26

.01

.38

.79

Romney Marsh .11

Roraney Marsh ,44

.99

.51

Great Britain Evans et al»,

1957

Great Britain Evans et al».

1957

Great Britain Evans et al.,

1957

Great Britain Evans et, al.j

1957

Australia France

Evans et. al., 1958

Evans et al., 1958

Great Britain Evans and

Blunt 1961

Australia

Norway

Norway

Evans and Blunt 1961

Efremov and Braend 1965

Efremov and Braend 1965

Britain were compared with the gene frequency in the Southdown breed in New South Wales. No obvious differ- ences in any other characteristics associated with dif- ferent hemoglobin types within the same breed have been

14

detected.

Two other hemoglobin types have also been detected in sheep, which are imder special conditions.

Harris and Varren (1955) identified the hemoglobin of norisal fetuses before birth from ewes of all three phenotypic hemoglobin types, but found only one type present which they designated Hb F, Drury and Tucker (1962) reported that 23 of 24 lambs at birth had both adult hemoglobin and Hb F, the latter being the major component. As the lambs grew older, the adult hemoglobins increased in amount until at about 30 days of age when no fetal (Hb F) hemoglobin could be detected.

The other new hemoglobin was observed in cells from the top erythrocyte layer of centrifuged blood of sheep with Hb A (Blunt and Evans, 1963). Vliet and Huisman (1964) reported a similar type of hemoglobin in sheep following experimental bleeding and called it Hb C. Braend et al. (1964) observed an elect rophoretic hemo- globin band, from a seven-month old anemic lamb, with a rate of migration on starch gel which was slower than that of Hb B. This hemoglobin type was named Hb N. Al- though no direct comparison has been made, based on rates of na-gration, Hb C was probably the same as Hb N.

Braend and Efremov (1965) found small amoimts of Hb N in 99 of 105 Norwegian (Spael) sheep, all of Hb A type. This suggested that Hb N may be a normal rather than an abnormal component. Sfremov and Bixiend (1966) found that Hb N occurred in relatively higher amounts in lambs than

15

in adults, with one-nionth-old lambs having an Hb N content as high as 30 percent of the hemoglobin.

In animals subjected to extreme experimental blood loss, the Hb A was replaced entirely by Hb C, whereas the production of Hb D apparently was not affected . Under conditions of moderate blood loss the replacement of Hb A by Hb C was only partial (Vliet and Huisman, 1964) . Following bleeding, little or no Hb A was observed in the young cells of the AB population, but Hb C appeared instead. Later, Hb A reappeared but Hb C persisted in the blood for at least 2 months (Drury and Tucker, 1965). No Hb B variant has been observed under anemic condition due to parasitic infections (Efremov and Braend, 1966) or experimental bleeding (Vliet and Huisman, 1964) . Blunt (1965) reported that a variant of Hb A produced during experimental anemia (probably Hb C) was located almost entirely in the reticulocytes. It was postulated that this variant is a relatively unfinished hemoglobin associated with the immature erythrocytes produced after a severe anemic stress. Schapira et al. (1962) con- cluded that the fraction of hemoglobin associated with young erythrocytes could have been either a special type of hemoglobin from red cells with a short lifespan, or a young, unfinished hemoglobin, which would eventually ac- quire the properties of the adult type.

The genetic control of the Hb A variants has not been completely determined. Braend and Efremov (1965) proposed that one of the structural genes controlling Hb N

16

is closely linked to one of the structural genes con- trolling Hb A. lib N commonly occurred with Hb A, but in very small quantities. Beale et al. (1966) concluded that the process by which Hb C forms the major propor- tion of the hemoglobin in anemic sheep of Hb A type is due to an increase in means or rate of synthesis of hemo- globin types rather than to the activity of a new gene. Wilson et al. (1966) indicated that the synthesis of the beta chain of Hb C is controlled by a structurally dif- ferent and "silent" gene, which is activated during severe anemia. The beta chain of Hb C was probably the product of a distinctive gene related to the beta chain of Hb A through gene duplication and remained linked in coupling (Boyer, 1967).

The hemoglobin proteins have been observed to differ in many physical and chemical properties. In addition to the varieties demonstrated by electrophoresis, dif- ferences were found to exist in oxygen affinity (Kernohan, 1961), in specific gravity and percent of dry matter (Hounib and Evans, 1959), in resistance to alkali (Blunt, 1965) and in amino acid composition (Helm et al., 1957).

Helm et al. (1957) found that Hb II in the sheep contained higher amounts of glutamic acid, threonine and serine, and lower amounts of aspartic acid, glycine and alanine. No differences in the peptide patterns of the alpha chains of the three adult hemoglobins >e re observed, but several amino acid differences in the beta chains of Hb A and B were observed (Muller, 1961 and Naughton et al., 1963). Vliet and Huisman (1964) reported that Hb A, B,

17

C, and F shared the same alpha polypeptide chain, "but the non-alpha chains of each of the four hemoglobin types were distinctly different. Huisman et al, (1965) pre- sented data which supported this hypothesis. Wilson et al, (1966) and Boyer et al.. (1967) have determined amino acid sequences of the non-alpha chains of the four hemoglobin types, and have shown minimum differences in residues present.

While a considerable amount of research has been reported on the physical and biochemical properties of the various hemoglobin types, little has been reported on the association of hemoglobin types with resistance to parasitic diseases. Evans et al. (1963) presented evi- dence that sheep with Hb A harbored fewer adult worms than sheep with Hb AB following infection with II, con- tortus. The trend in ova counts and worm counts at the height of H. contortus -induced anemia suggested an inter- action between hemoglobin type and susceptibility to H. contortus might exist, the animals with Hb A being the less susceptible,

Evans and Evans (1964) showed a relationship between hemoglobin types and hematocrit values. The mean hema- tocrit values for Hb A were greater than those for Hb B, with the mean hematocrit values for Hb AB intermediate.

King et al,. (1958) found no significant differences in reproductive performance or growth rate of ewes of different hemoglobin types. The number of lambs produced by ewes of different hemoglobin types did not differ sig-

18

nifioantly, although there was some suggestion that hemoglobin heterozygotes produced a slightly larger number of lambs, Evans and Turner (1965) reported that ewes with Hb A had fewer lambs born or weaned than those with Hb AB or B, while the difference between Hb AB and B was slight. The main source of difference in lambs bom in the various flocks was in the proportion of mul- tiple births. The superiority of the Hb B ewes appeared to be associated with the production or survival of lambs from multiple births.

MATERIALS AND MSTTIODS

BaSlo Design and Management Pi-'actjces

The basic design was a 2 X 2 factorial, with two foundations (120 Florida Native ewes and 60 Rarabouillet ewes) and two levels of resistance to H. contortus (high and low). Assignment to the high or low resistance level groups was based on the mean value of periodic hemoglobin determinations over a two-year period. Animals from each breed were ranked according to this mean hemoglobin value and divided at the median into two equal groups. Those ewes with hemoglobin means above the median were assigned to the "high resistance" groups; those below into the "low resistance" groups.

TABLE 2

Experimental Design Niimber of Ewes per Resistance Group

Foundation Resistance

High Low

Florida Native 60 60

Rambouillet 30 30

The entire flock was maintained on 25 acres of per-

19

20

raanent Coastal Bermudagrass pastures at all times as one flock except for a 45-day breeding season which began on July 1 of each year. This continuous grazing of perma- nent pastures assured a high exposure rate to H. contortus. Supplemental feeding of Coastal Bermudagrass hay (free choice) and one to two pounds of a corn-soybean meal concentrate per head was provided the ewe flock when pasture conditions were inadeq.uate.

Anthelmintic treatments were initially eliminated from all groups to allow genetic resistance potential to be manifested. As a result, death losses increased in the Rarabouillet ewes to the extent that the low re- sistance group was in danger of being eliminated from the experiment. Consequently, very anemic Rambouillet ewes were treated with phenothiazine in an effort to reduce the adult H. contortus load and prevent death. All drenched ewes were allotted to the low resistance group. Therefore, survival without anthelmintic treat- ment became the criterion for selection in the iiambouillet ewes.

Ewes were culled on age and failure to fit into the resistance group for which they were selected. Natural selection, n^anifested in death losses, was so strong in the Rambouillet ewes that no culling was permissible.

All physically sound ewe lambs were kept as replace- ment ewes. Replacement lambs were placed with the ewe flock after the breeding season to challenge them with natural infections of 11. contortus. Mean hemoglobin

Zl

level from weaning to 18-months of age was used to deter- mine the resistance group into which a replacement ewe was placed.

Warwick et al,. (1949) reported that it was necessary to have intense selection for resistance to H. contortus on both sides of the pedigree to make progress through selection. Rams were selected on mean hemoglobin level. Hemoglobin type of the ram was included in selection of sires for the 1967 breeding season. An attempt was made to increase the frequency of Hb A in the high resistance groups and the frequency of Hb B in the low resistance groups by the selection of the sires on hemoglobin type in 1967 (Table 3). Two rams were placed with each breed by resistance sub-group except for the high resistance Rambouillet group which had only one ram in 1967. Re- placement rams were selected from ewes which best fit their respective resistance group (from ewes with highest hemoglobin levels in the high resistance groups and from ewes with lowest hemoglobin levels in the low resistance group.

A "sample flock" which consisted of one-sixth of each breed-resistance group was selected at random from within the breed-resistance groups and maintained with the re- mainder of the flock at all times. The sample ewes were used to study the relationships between hemoglobin levels, as an indicator of resistance to H. contortus . and total gamma globulin levels, ova counts and hemoglobin types. The ewes were sampled at one-month intervals for one com-

22

TABLE 3

Hemoglobin Typo of Sires for 1967 Breeding Season

Breed

Number

Hemoglobin Type

Resistance Group to li/hich Hated

Florida Native

N20

AB

Low

N21

B

Low

N80

A

High

N8I

AB

High

NS2

AB

Spare

Rambouillet

ROl

B

Low

R02

AB

High

R80

B

Low

plete year (December, 1966, to November, 1967). ^Vhen a ewe from the sample flock died, it was replaced by a comparable ewe from the same breed-resistance group.

Resistance of Slieeo to Ilaemonchus contortus

Immunology and Hematology

Blood samples were collected from the entire sheep flock at two-month intervals from an ear vein. Blood samples v/ere collected into henarinized capillary tubes and hemoglobin pipettes.

A microtechnir; o using heparinized capillary tubes was employed for packed cell volume determination. Each

23

tube was filled with blood, sealed at one end with

plastic clay and centrifuged at 11,500 rpm for five

1 minutes in a Model MB centrifuge. At the completion

of the cycle, the tubes \jere placed in a raicrocapillary

2

tube reader and the packed erythrocyte column measured

as packed cell volume percent for each sample.

The acid-hematin technique of Cohen and Smith (1919) was employed for hemoglobin level determination. In a hemoglobin pipette, 0.025 ml. of whole blood was added to 5.0 ml. of one percent hydrochloric acid solution and allowed to stand at room temperature for one hour.

The percent transmission of the sample was measured in a

3

spectrophotometer at a wave-length of 525 millimicrons

and converted into grams of hemoglobin per 100 ml. of blood.

At one-month intervals, viwo blood samples from each ewe in the "sample flock" were obtained by venipuncture of the jugular vein with a 20-gauge disposable needle. A whole blood sample was collected into a 4 ml. Vacutainer tube containing ethylenediaminetetraacetic acid (EDTA) as an anticoagulant and a second sample was collected into a 10 ml. Vacutainer tube containing no anticoagulant, to

International Equipment Company, Needhara Hts., Mass.

^Ibid.

3

Bausch and Lomb Spectronic 20.

24

obtain serum. In the laboratory, packed cell volumes and hemoglobin levels were determined by the methods described above.

The method of Jager and Nickerson (1948) was employed for the determination of total serum gamma globulins. One ml. serum and 0.5 ml. saturated ammonium sulfate were placed in a 15 ml. centrifuge tube, shaken and refriger- ated at four degrees C. over night. The suspension was then centrifuged, the liquid removed, and 3.0 ml. of 33.3 percent saturated ammonium sulfate added to the precip- itate. After stirring and cent rifuging the suspension, the liquid was removed and the precipitate was dissolved in ten ml. of 0.85 percent sodium chloride. Five ml. of the sodium chloride solution was added to five ml. biuret

reagent and the percent transuiission of the solution was

1 measured in a spectrophotometer at a wavelength of 540

millimicrons and converted into grams gamma globulin per

100 mL -f serum.

Parasitology

Fecal samples were collected from each ewe in the flock in July and September, 1966, to measure the effec- tiveness of selection. Fecal samples were also collected from the sample ewes at monthly intervals from December, 1966, to November, 1967. Ova counts were determined by the McMaster slide flotation technique ('.Vhitlock, 1948).

Since mixed, natural parasitic infections were used.

Bausch and Lomb Soectronic 20.

25

larval identification was necessary to determine the types of nematode infections present. About five grams of feces were cultured at room temperature for seven days to permit development of the larvae. The larvae were collected with a Baermann funnel (Morgan and Hawkins, 194-9) and identified as to species (Skerman and Hillard, 1966).

Aboraasal worm counts were obtained from most of the sheep which died and from 20 Florida Native ewes culled and slaughtered in January and February, 1968, to deter- mine H. contortus incidence in the flock. All adult H. contortus present in two 20-ml. aliq.uots of the abo- masal contents and washings were counted and multiplied by the appropriate factor to obtain total worm counts.

Hemoizlobin Types of Sheen

After hemoglobin levels and packed cell volumes were determined on the whole blood samples from the ewes of the "sample flock" in February, 1967, the red blood cells from the remainder of each sample were saved for hemo- globin type determination. Blood samples were obtained from the remainder of the flocJv using the same technique. The red blood cells were washed with 0.85 percent physi- ological saline and hemolyzed with distilled water to release the hemoglobin for electrophoresis.

A modification with vertical gel of the starch gel method described by Siaithies (1955) was used for hemo- globin type determinations in this study. A 0.06 M Tris-

26

EDTA -"borate "buffer with a pH of 9.0 (12.1 grams Tris, 0.9 <rraa;s "boric acid, 1.6 grams Nao EDTA and distilled V.-- ter to bring buffer volume to 2000 ml.) was used to suspend the hydrolyzed Connaught starch. A 0.12 M barbital buffer with a fd of 8.6 (24,7 grams sodium barbital, 3.4 grams diethylbarbituric acid and distilled water to bring buffer volume to 1200 ml.) v;as used as the electrode buffer. The power supply v;as set to deliver 250 to 300 volts with the milliamps not ex- ceeding 50 and allowed to run 1^- to 2 hours. The gel was then cut to the desired size, removed from the tray and sliced with a cutter set at 4.0 mm. depth. The two halves were separated and stained with aniline stain.

Lambs were weighed at 70 -days of age to determine production of the ewes with each hemoglobin type. Ewes were weighed at two-month intervals to determine if weight differences are present betv/een hemoglobin types.

iiSSULTS Resistance of Sheep to Haemonchus Contortus

The deviations in the number of ewes per breed- resistance group are shown in Table 4. Death losses

TABLE 4

Deviations in the Number of Ewes and Death Losses by Resistance Groups

Dates

Florida Native High Low

Rambouillet High Low

Number of ewes

August, 1966

60

60

31

31

October, igee*:*

60

60

26

30

February, 1967

58

59

22

29

April, 1967

56

57

19

28

Replacement

ewes added

4

4

3

5

June, l9o7

59

58

21

29

August, 1967*

59

58

15

34

October, 1967

59

58

15

27

February, 1968

59

Death

58 losses

14

24

October, 1966

0

0

3

3

February, 1967

2

1

4

1

April, 1967

2

2

3

1

June, 1967

1

3

1

4

August, 1967

0

0

0

1

October, 1967

0

0

0

7

February, 1968

0

0

1

3

Total death loss

5

6

12

20

*Reallotment of Rambouillet ewes

27

28

reduced the number of ewes in each group "below the number described in the basic design of the study. Forty-six percent of the Rambouillet ewes died during the two years, while only nine percent of the Florida Native ewes died during the same period of time. Fourteen iiambouillet ewes had survived without anthelmintic treatment. Immunology and Her.atology

Mean packed cell volumes and hemoglobin levels of the ewe flock obtained at two-month intervals are shown in Table 5. The Florida Native ewes maintained higher levels in both values than the Rambouillet ewes. Within breed, the high resistance group levels were higher than the low resistance group levels. The Ram- bouillet ewes in the high resistance group were anemic for the last two sample periods.

Mean packed cell volumes, hemoglobin levels and total gamma globulins of the sample ewes are shown in Table 6. Breed and resistance group differences in packed cell volvunes and hemoglobin levels similar to these for the whole flock v;ere observed. Florida Native ewes had higher total gamma globulin levels than the Rambouillet ewes, indicating a positive correlation between resistance and total gamma globulins. Within breeds, the low resistance groups had higher total gamma globulin levels than the high resistance groups, indi- cating a negative correlation between resistance and total gamma globulins. A non-significant, positive re- lationship (0.02) was observed between total gamma

29

TABLE 5

Moan Packed Cell Volumes and Henioglo"bin Levels of the Ewe Flock

Florida

Native

Rarabouillet

Dates

High

Low

High

Low

Packed cell

volume

iio)

October, 1966

34.8

31.4

31.3

25.4

December, 1966

31.7

29.2

26.4

25.3

February, 1967

28.9

27.0

25.4

24.7

April, 1967

27.8

26.2

25.9

25.9

June, 1967

28.5

26.0

24.4

21.9

August, 1967

31.1

29.0

28.4

24.6

October, 1967

32.7

29.7

27.8

22.6

December, 1967

29.9

27.7

22.4

23.4

February, 1968

29.4

26.0

20.4

25.8

Hemoglobin level (g./lOO

ml.)

August, 1966

8.45

7.52

7.85

7.28

October, 1966

9.56

8.00

8.33

5.77

December, 1966

9.03

8.15

7.13

6.91

February, 1967

7.17

6.93

6.13

5.95

April, 1967

8.23

7.85

7.40

7.39

June, 1967

8.29

7.40

6.85

5.98

August, 1967

9.01

8.29

8.15

7.00

October, 1967

7.64

6.94

5.88

5.10

December, 1967

6.78

6.37

4.04

4.18

February, 1968

6.72

6.04

4.54

5.99

30

TABLE 6

Mean Packed Cell Volumes, Hemoglobin Levels and Total Gamma Globulins of the "Sample Flock"

Florida Native

Rambouillet

Month

High

Low

High

Low

Packed

cell volume

^io)

1

December

28.4

25.8

22.8

20.4

January

26.6

22.3

21.8

15.5

February Ma rch April May

28.4 27.3

24.9 24.7

22.5 20.8

15.3 20.1

26.7

22.8

22.3

21.6

27.2

24.4

24.7

21.9

June July- August September October November

27.4

24.2

23.8

22.1

27.9

28.8 28.4 31.5 31.8

25.2 27.6 26.3 27.5 26.6

30.7

29.8 28.5 28.7 28.8

24.6 23.8 24.2 24.6 22.7

Hemoglobin level (g./lOO

ml.)

December

9.6

8.6

6.8

5.7

January

9.2

7.4

7.0

5.3

February-

10.0

9.5

8.3

5.1

March

10.2

9.1

6.7

6.0

April

10.1

8.7

8.1

7.8

May

9.5

8.6

8.2

7.8

June

9.2

8.1

7.3

6.9

July

8.8

8.2

10.4

8.1

August

10.7

7.5

9.7

7.4

September

9.5

8.6

9.3

7.6

October

10.4

8.5

8.4

7.8

November

10.4

8.6

9.9

7.5

Total gamma

globulins (g

./I

00 ral.;

)

December

0.81

1.02

1.12

1.28

January

1.29

1.69

1.04

1.17

February

1.95

2.28

1.45

1.60

Ma rch

2.16

2.28

1.65

2.01

April

2.04

2.27

1.98

1.98

May-

2.20

2.25

1.97

1.99

June

1.91

2.23

1.81

1.54

July

2.23

2.07

1.57

1.96

August

2.36

2.23

2.02

2.07

September

1.62

1.95

1.42

1.60

October

1.80

2.08

1.45

1.54

November

1.64

1.78

I.IS

1.39

31

globulins and hemoglobin levels. Para sit olojyy

Mean H. contortus ova counts, taken in July and September, 1966, to determine the effectiveness of selection, are shown in Table 7. Ii/hile large breed

TABLE 7 Helminth Ova Covmts from Ewe Flock*

Florida Native High Low

Rambouillet High Low

Mean ova per

gram of feces

July, 1966 93

September, 1966 80

Percent samples with less than 200 ova per gram of feces 92.5

Percent samples with more than 1,000 ova per gram of feces 2.5

. 42 534 577 163 1288 3310

91.7 53.8 36.7

1.7 21.2 41.7

» 7^94% H. contortus

differences in the means exist, within breed resistance group differences were generally small. No helminth ova were observed in the samples from a large percent of the ewes in all groups. Over ninety percent of the Florida Native ewes had counts of less than 200 ova per gram of feces. The Rambouillet high and low resistance groups had 53.8 and 36.7 percent of the ewes, respectively, with counts of less than 200 ova per gram of feces. Only

32

alaout two percent of the Florida Native ewes had counts of more than 1000 ova per gram of feces. The llambouillet high and low resistance groups had 21.2 and 41.7 percent of the ewes, respectively, with counts of more than 1000 ova per gram of feces.

Breed differences in the mean ova counts of the "sample flock" can be divided into two periods (Table 8). During the first period, December through June, the ova counts were lower in the Florida Native ewes than in the Rambouillet ewes. During the second period, July through November, the differences were small. In the Florida Native flock, the high resistance grovip had lower ova counts than the low resistance group. A significant, negative relationship (-0.32, P<33.01) was observed between ova counts and hemoglobin levels. Over 90 percent of the ova in the feces were identified by larval cultures as H . contortus.

Mean necropsy H. contortus counts obtained on ewes which died are shown in Table 9. The stonuchs of two of the high resistance Florida Native ewes contained large amounts of sand. Several of the low resistance Rambouillet ewes were drenched with phenothiazine shortly before death. These factors reduced the mean counts of the respective groups.

Necropsy H. contortus counts for Florida Native ewes culled during each of the two months were very low (Table 9) The entire stomach contents were screened in January since the samples failed to show any worms. The mean counts from

33

TABLE 8

Helminth Ova Counts* And Larval Cultures from "Sample Flock"

Month

Florida Native High Low

Ramhouillet High Low

Ova per gram feces

December

January

February

Ma rch

April

May

June

July

August

September

October

November

December

January

February

Ma rch

April

May

June

July

August

September

October

November

1680

3070

6920

6220

2070

2710

6920

8660

167

344

9525

6400

50

511

3800

400

70

430

400

1467

40

390

1467

3175

388

588

900

1660

70

356

167

350

60

310

50

317

67

457

33

283

70

256

300

471

475

370

1000

960

ures (?^

Haemonchus

contortus)

100

99

99

98

96

95

98

99

97

100

100

100

95

98

100

95

98

94

99

100

96

93

85

93

92

96

92

97

92

86

95

95

86

94

96

98

83

79

97

95

94

88

100

75

92

91

97

99

*7^94^ H. contortus

34

TABLE 9

Necropsy Haemonchus contortus Counts On Ewes l^Tiich Died and Culled Ewes

Florida Native High Low

ilambouillet High Low

Number sampled Mean H. contortus counts

January, 1968 Number sampled Mean H, contortus counts

February, 1968* Number sampled Mean H. contortus counts

Ewes which

died

5

5

10

9

10880

12500

12230

11311

Culled

ewes

4

4

5

4

6

6

283

550

*Many inuaature worms present

the ewes culled in February were higher than those culled in January. Many of the worms found in February were immature worms. Both groups of cull ewes, however, had much lower mean H. contortus counts than the ewes which had died. Two ewes slaughtered in February were very anemic (hemoglobin levels a" 3.8 and 4.4 grams percent) but had only 1400 and 2100 H. contortus. respectively, at necropsy. \»aiile these were the two highest counts, they were considerably lower than the counts from ewes which had died.

35

Hemoglobin Types of Sheep

Hemoglobin types were determined on blood samples from the 30 sample ewes (Table 10). A greater incidence

TABLE 10

Hemoglobin Types of "Sample Flock" by Resistance Groups

Resistance Hemoglobin Type Breed Group 4 AB B ABC

Florida Native High 3 7 1

Low 3 3 4

Rarabouillet High - 1 3

Low - 14

of the Hb A gene was observed in the Florida Native ewes than in the Rambouillet ewes. No Hb A ewes were found in the Rarabouillet sample group. There was a trend toward greater incidence of the Hb A gene in the high resistance groups than in the low resistance groups. Hb C was found in one very anemic Rambouillet ewe^ along with Hb AB.

Figure 1 is a photograph which shows the various hemoglobin types observed in the sheep flock. The samples migrated for two hours on a power source deliver- ing 290 volts and 48 milliamps, and were stained with aniline stain. The origin of the migrations is at the top of the starch gel. The Hb A fraction migrated the great- est distance from the origin, the Hb C fraction migrated

§i|ii#||^« 4t

t a 345-676^/,

Figure 1. Starch gel showing hemoglobin types found in Florida sheep

37

the shortest distance from the origin and the Hb B fraction migrated the intermediate distance from the origin.

Samples 1 and 10, from six-month old Florida Native lambs, were Hb Ali. The dam of the first lamb had Hb A (sample 2). Another dam-daughter pair (samples 3 and 4, respectively) had Hb B. Hb C was found in only two sheep; the Rambouillet ewe mentioned above with Hb ABC (sample 5), and a 10-year old Florida Native ewe with Hb AC (sample 6), A llambouillet ewe had Hb B (sample 7) and a Florida Native dam-daughter pair (samples 8 and 9, respectively) had Hb A. Two of the lambs (samples 4 and 9) are from one-month old lambs. No Hb F was present in either sample, llie stained masses above the hemoglobin fractions are impurities that were not removed during preparation.

The number of ewes per hemoglobin type in each resis- tance group are shown in Table 11. Breed differences for hemoglobin type were large and highly significant. No Hb A ewes were present in the Harabouillet flock, while 39 percent were present in the Florida Native flock. The gene frequencies for Hb A were 0.190 for the Ram- bouillet ewes and 0.558 for the Florida Native ewes.

It was observed that the aged Florida Native ewes (9-, 10- and 11-years of age) had a high incidence of Hb A but 15 of the 18 ewes were in the low resistance group. The assvunption was made that ewes which live to this age must have some resistance and, therefore, the low

38

TABI£ 11

Hemoglobin Type of Ewe Flock by P^ssistance Groups

Resistance Hemoglobin Type

Breed Group A AB B AC ABC

" * e

""■

High

21

24 11

-

Low

14

14 18

-

High

Z

1 -

-

Low

8

3 3

1

Florida Native (less than 9 -years of age)

Florida Native (9-, 10- and 11- years of age)

gene freq.uency for Hb A 0.558

Rambouillet High - 6 9

Low - 12 ZZ

gene frequency for Hb A 0.190

hemoglobin percents may be due to some aspect of aging. An examination of the teeth of several of these ewes revealed very poor, or almost complete absence of teeth. Because of these facts, the Florida Native ewes were classified into two age groups.

Chi squared analysis (Snedecor, 1962) of the dif- ferences between high and low groups within the Florida Native ewes (less than 9-years old) approached signi- ficance at the 5 percent level. Hb A was more prevalent in the high resistance group and Hb B was more prevalent in the low resistance group.

The effects of hemoglobin type on hemoglobin level, packed cell volume and weight of the ewes are shown in

39

Table 12. Hemoglobin type had a highly significant effect on hemoglobin level and packed cell volume. Ewes

TABLE 12

Least Squares Analyses for Hemoglobin Level, Packed Cell Volume and Body Weight of Ewes

Source

d.f.

Hemoglobin Level

Packed

Cell Volume

Weight of

Ewes

Total 701

Hb type (T) 2

Season (S) 5

T X S 10

Animal (A) 116

A:T 114

AS:T 570

21.14** 396.41** 338.53

65.29** 287.86** 9185.64**

1.72* 6.17 36.55

3.46** 48.01** 412.06**

.75 6.35 32.09

*P<0.05 **P<0.01

with Hb A had higher mean hemoglobin levels and packed cell volumes than ewes with Hb B (Table 13). Differences between ewes with the Hb A and ewes with Hb Ab were small. The effect of hemoglobin type en' the weight of the ewes (Table 12) was not significant.

Season had a highly significant effect on all three traits (Table 12). The hemoglobin type by season inter- action was significant only for hemoglobin level. Theo- retically no good error term was present to test the sig-

40

TABLE 13

Mean Hemoglobin Level, Packed Cell Volumes and Weights of the Ewes by Hemoglobin Type of the Ewes

Sample month (season)

Hemoglobin Type A AB B

February

April

June

August

October

December

Average

February

April

June

August

October

December

Average

February

April

June

August

October

December

Average

Hemoglobin level (g./lOO ml.)

7.50

7.08

7.02

8.60

8.04

7.59

7.92

8.05

7.49

S.S4

8.90

8.07

7.29

7.56

6.98

6.60

6.79

6.15

7.79 7.74 Packed cell volurae (%)

29.8 29.2 Weight of the ewes (pounds)

7.22

29.7

28.2

27.4

28.6

27.4

25.4

28.1

27.5

25.7

31.0

30.8

28.3

31.9

32.0

29.1

29.5

29.1

27.2

27.2

89.5

92.1

92.3

79.3

80.6

80.7

81.7

83.0

82.9

85.9

88.8

87.5

90.9

94.0

90.8

104.6

107.0

103.1

88.7

90.9

89.6

nificance of the mean squares for animals within hemo- globin type (A:T). The best estimate (Henderson, 1960) was the moan square for animal X season within hemoglobin type (Ai>;T). The ratios of these two variances were

41

large, clearly demonstrating a significant difference between animals of the same group.

The relationship "between hemoglobin type and re- productive performance of Florida Native ewes is shown in Table 14. Ewes with Hb B had a higher percent of

TABLE 14

The Relationship Between Hemoglobin Type and Reproductive Performance of Florida Native Ewes

Reproductive Performance of ewes

Lamb Crop

Hemoglobin Type A AB B

barren ewes {%)

single lamb (%

twin lambs (%

1967 1968

Total 1967 1968

Total 1967 1968

Total

4.8

7.3

3.3

20.9

26.2

25.8

12.9

16.9

14.7

83.3

75.6

70.0

69.8

64.3

61.3

76.5

69.9

65.6

11.9

17,1

26.7

9.3

9.5

12.9

10.6

13.2

19.7

twin births than ewes with Hb A, although Chi squared analysis did not show the difference to be significant. Ewes with Hb A had the highest percent of single births* Ewes with Hb B had the lowest percent barren ewes in 1967, while ewes with Hb A had the lowest percent barren ewes in 1968.

42

Least squares constants of 70-day weights of Florida Native lambs are shown in Table 15. Type of birth had a

TABLE 15

Least Squares Constants for 70-day V/eight (Pounds) by Type of Birth, Hemoglobin Type of Dam and Lamb

Variable 70-day Weight Variable 70-day Weight

Type

of Birth**

General Mean

32.43

sin,

gle lambs

3.015

twin lambs

-3.015

Hemoglobin type of the lamb

Hemoglobin type

of the dams

Hb A

-0.235

Hb A

-0.03

Hb AB

-0.745

Hb AB

1.34

Hb B

1.905

Hb B

-1.31

N.D.*

-0.925

*Lambs disposed of before blood samples could be

taken for hemoglobin type determination **p<^0.01

highly significant effect on the 70-day weight of the lambs. Lambs from single births were 6.03 povmds heavier than lambs from twin births. Neither hemoglobin type of the ewe or of the lamb had significant effects on the 70-day weights of the lambs.

DISCUSSIOiN Resistance of Sheep to Haemonchus contortus

Death loss in the xHarabouillet ewes was higher than in the Florida Native ewes even though many of the Rarn- bouillet ewes were drenched with phenothiazine and none of the Florida Native ewes were drenched. Fourteen Ram- Toouillet high resistance ewes had survived without anthel- mintic treatment. The fact that some Rambouillet ewes had survived without anthelmintic treatment would indi- cate that variability in resistance level is present in the Rambouillet ewes. Immunology and Hematology

The packed cell volume and hemoglobin level within animals showed a large amount of fluctuation. This fluctuation may be caused by the "self -cure" phenomenon as reported by Stoll (1929).

Large breed differences were present in the packed cell volume and hemoglobin level data. These results agree with the results of Loggins et al. (1965) in which Florida Native ewes had higher hemoglobin levels than Rambouillet ewes. Holraan (1944) and Becker and Smith (1950) observed no significant breed differences for packed cell volumes or hemoglobin levels. The breeds used in the present study and by Loggins et al. (1965) were

43

44

different in their adapta"bility to Florida conditions. The Florida Native breed was developed by natural selection under Florida production conditions (jilek, 196G). The ilambouillet breed was imported from Texas and Alabama and was not well adapted to Florida produc- tion conditions. The breed differences would then appear to be the result of differences in parasitic burdens.

The gamma globulin fractions of blood serum are generally associated with an immune response. The results, obtained in this study, which show that total gam;jia globulin levels were not associated with hemoglobin levels, would suggest either that there was no immune response present or that relative increases and decreases of specific fractions of gamma globulins were associated with immunity. Parasitology

Within animal observations on ova counts showed a large amount of fluctuation during the course of this study. The decrease in ova counts was more rapid than the increase in packed cell volume or hemoglobin level and these results also suggest that a "self -cure" phe- nomenon was operating.

The highly significant, negative relationship between hemoglobin level and ova counts observed in this study is not in agreement with the observations of Kingsbury (1965), in which no relationship was observed. Ewes with very high ova counts had low hemoglobin levels. These extreme values increased the magnitude of the negative relation-

45

ship. Ewes with low ova counts did not necessarily have high hemoglohin levels.

Mean necropsy worm counts from the Florida Native ewes which had died (11, 690 H. contortus) were much larger than the mean necropsy worm counts of the culled ewes which were sacrificed (250 K. contortus) . This would indicate that necropsy count on ev;es which die is not a good measure of the parasitic load of the flock. The worm burden of very anemic ewes would seem to increase greatly just before death. The precarious existence of the parasites may necessitate this in- crease prior to the death of a host.

There are two possible explanations for the lower necropsy worm counts in January than in February. First, the ewes culled in January were barren ewes or ewes which lost their lambs at an early age. These ewes were not stressed from parturition and lactation as were the lactating ev;es. Two of the ewes which were sac- rificed in January were anemic. However, the necropsy worm counts on these ewes were low. Second, "self -cure" may have reduced the nvunber of worms in the ewes just prior to the sacrificing of the ewes in January. The niimber of immature worms present in the ewes sacrificed in February would indicate that 'feelf -cure" had occurred and new infections were developing.

46

nemog:lo"bin Types of Sheep

"Self -cure," a dynamic cyclic phenomenon, influences the henatological and parasitological values of a sheep. If resistance is measured by one of these parameters, the level of resistance will he influenced by the particular phase cf the "self -cure" cycle of the animal. An animal sampled just prior to expulsion of the v;orms may there- fore appear to have very little resistance to H . contortus since hematological measurements will be low and parasi- tological measurements will be high. On the other hand, the same animal sampled just prior to establishment of a new infection may appear to have a high resistance to H. contortus since henuitological measurements will be high and parasitological measurements will be low.

One solution to this problem is to select a discrete variable which is correlated v;ith resistance levels as the parameter for estimating resistance. The discrete variable examined in this investigation is hemoglobin type. The results of Helm et al. (1957) and Huisman et al. (1958) indicate that the hemoglobin types are gen- etically determined in a simple Mendelian manner. The only reported changes in an animal's adult hemoglobin type have involved the production of lib C in very anemic sheep having Hb A (21unt and Evans, 1963; Braend et al., 1964; Vliet and Huisman, 1964). If the hemoglobin types can be shown to be correlated with the resistance of sheep to H. contortus. the phase in the "self -cure" cycle of the

47

animal when the sample is obtained will not iafluence the determination of the resistance levels.

The design of this experiment does not permit the determination of the inheritance of hemoglobin type. Multiple sires of different hemoglobin types were used in each breed group. Ewes with Hb A gave birth to lambs with either Hb A or AB and ewes with Hb B gave birth to lambs with either Hb B or AB. V/hile the inheritance of hemoglobin type could not be studied in detail, no evi- dence was observed to refute the type of inheritance reported in the literature.

Hb C was observed in only two ewes, "both of which also had Hb A. If the sheep had been sampled periodically through the year, it s possible that more sheep would have had some Hb C .

The facts that Florida Native ewes have a high fre- quency of Hb A and are adapted to Florida production conditions may indicate that Hb A sheep are adapted to the adverse conditions that are present in Florida. These results are in agreement with those of Evans and Blunt (1961) in which the frequency of Hb A or AB was higher under more advei-'se conditions than under less adverse conditions. Adaptation to Florida production conditions would include increased resistance to H. contortus in- fections.

The analyses of resistance group differences within the Florida Native breed and of the effect of hemoglobin

48

type on heniatd.ogical values indicate, likewise, that sheep with II"b A are more resistaiat to parasites than sheep with H"b B. Evans et al, (1963) reported that trends in ova counts and in worm counts post mortem at the height of the anemia induced by U. contortus suggest that an interaction between hemoglobin type and sucep- tibility to H. contortus may exist. The sheep with Hb A are the less susceptible sheep. Evans and Evans (1964) found that a close relationship exists between hemoglobin type and hematocrit values.

A large increase in the percent of barren ewes was observed in 1968 as compared oo 1967. The percent ewes giving birth to twin lambs decreased in 1968 as compared to 1967. A loss of weight by the ewes prior to the 1968 lambing season may have caused this decrease in repro- ductive rates. The mean weigh v of the ewes was less than 90 pounds during the 1968 breeding season. Coop (1962) found that barrenness increased rapidly in ewes below 90 pound liveweight. Many of the ewes in the present study were below this critical weight.

The effect of hemoglobin type on production is mainly in the proportion of multiple births. The mean weight of the lambs from the Hb B ewes was lower than the mean weight of lambs from Hb A or AB ewes. Lambs born as twins weighed less at weaning tha;: Ic. " s born as siiigles (Shelton and Carpenter, 1957). '.Iiile the individual lambs from Hb B ewes weighed less, there were more of them to increase the production per awe bred over the Hb A and AB

49

ewes. Evans and Turner (1965) observed that ewes of Hb A had fewer lambs born or weaned than those of Hb AB or B. Least squares analysis of the 70-day weights in 1967 showed that differences in the weights between the hemoglobin type groups was due mainly to the type of birth. The results of this study are in agreement with those of Evans and Turner (1965). The superiority of the Hb B ewes appears to be associated with the production or survival of lambs from multiple births.

This study was conducted over a two-year period using 60 llambouillet and 120 Florida Native ewes. Each breed group was divided into high and low resistance groups using mean hemoglobin levels as indicators of resistance to n. contortus infections.

Death loss was greater in the Rambouillet than in the Florida Native ev/es. Only 14 of 70 (original allot- ment plus replacements) Rambouillet ewes survived without anthelmintic treatment.

Florida Native ewes were consistently higher in hemoglobin levels and packed cell volumes than Rambouillet ewes. Within breeds, the high resistance group was higher in both values than the low resistance group. A non- significant, positive relationship (0.02) was observed between total gamma globulins and hemoglobin levels.

Large breed differences were observed in mean H, contortus ova counts. However, a large percent of the ewes in both breed groups had very low ova counts. A signi- ficant, negative relationship (-0.32, P<^0.01) was observed between ova counts and hemoglobin levels. Tliis significant relationship can be explained by the very anemic condition of ewes with very high ova counts. Over 90 percent of the ova in the feces were identified by larval cultures as

50

51

H, contortus.

The mean necropsy worm count on ewes which died was 11,690 H. contortus. Breed difx^erences for necropsy counts on ewes which died v/ere small. The mean necropsy worm count on culled Florida Native ewes was only 250 n. contortus^ indicating that the necropsy counts on ewes which died were not good measures of the parasitic burden of the flock.

A higher incidence of the Hh A gene was observed in the Florida Native breed and in the high resistance groups than in the Rarabouillet breed and lov; resistance groups, respectively. Resistance group differences within the Florida Native breed approached significance at the five percent level.

Hemoglobin type had a highly significant effect on hemoglobin level and packed cell volume. Ewes with Hb A or AB had higher-mean hemoglobin levels and packed cell volumes than ewes with Hb B. ,

The effect of hemoglobin type of production was mainly in the proportion of multiple births. Twinning percent was higher in Florida Native ewes with Hb B than in Florida Native ewes with Hb A.

These results would indicate that ewes with Hb A may be more resistant to parasitic infections with H. contortus than with ewes with Hb B. Ewes with Hb B, however, may be more prolific and have greater production per ewe than ewes with Hb A.

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59

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BIOGMPHICAL SKETCH

Anthony Francis Jilek was born July 11, 1942, in Barron County, V/isconsin. In May, 1960, he was grad- uated from Rice Lake High School, Rice Lake, Wisconsin. He attended Wisconsin State College, River Falls, from which he received the degree of Bachelor of Science in Agricultural Education in June, 1964.

In September, 1964, he began graduate work at the University of Florida. He received the degree of Master of Science in Agriculture in June, 1966. He continued his predoctoral studies at the University of Florida and is a candidate for the degree of Doctor of Philosophy in June, 1968.

Mr. Jilek is married to the former Anne Boortz and is the father of two daughters, Jodi Anne and Amy Frances He ±! a member of Alpha Zeta, Kappa Delta Pi, and the American Society of Animal Science.

This dissertation v;as prepared under the direction of the chairman of the candidate's supervisory committee and has been approved by all members of that committee. It was submitted to the Dean of the College of Agriculture and to the Graduate Council, and was approved as partial fulfillment of the requirements for the degree of Doctor of Philosophy.

June, 1968

iJjA

5^ Dean, College of Agriculture

Dean, Graduate School

Supervisory Committee

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