Title: Experimental evidence of resistance to Haemonchus contortus infection in sheep /
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Permanent Link: http://ufdc.ufl.edu/UF00097801/00001
 Material Information
Title: Experimental evidence of resistance to Haemonchus contortus infection in sheep /
Physical Description: 60 leaves : ill. ; 28 cm.
Language: English
Creator: Jilek, Anthony Francis, 1942-
Publication Date: 1968
Copyright Date: 1968
Subject: Sheep -- Diseases   ( lcsh )
Domestic animals -- Parasites   ( lcsh )
Animal Science thesis Ph. D
Dissertations, Academic -- Animal Science -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis (Ph. D.)--University of Florida, 1968.
Bibliography: Bibliography: leaves 52-59.
Additional Physical Form: Also available on World Wide Web
Statement of Responsibility: by Anthony Francis Jilek.
General Note: Typescript.
General Note: Vita.
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Bibliographic ID: UF00097801
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000406505
oclc - 24680928
notis - ACF2776


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The author wishes to express his sincere appreciation

and gratitude to Dr. Marvin Koger, Chairman of the Super-

visory Committee, for his invaluable council and assistance

throughout this study and the preparation of this disser-

tation. Further appreciation and gratitude are expressed

to Dr. R. E. Bradley, Dr. G. T. Edds, Dr. A. C. Warnick

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



ACK OWLEDGENT . . . . . . ii

LI6T OF TABLE . . . . . . . iv

INTRODUCTON . . . . . . . 1

LITEiLATUIUE REVIEW . . . .... ... 4

Life Cycle and Pathogenesis of Haemonchus
contortus. . . . . . .. 4
Resistance of Sheep to IIaemonchus
contortus . . . . . . 5
Immunology. .. . . . . 5
Hematology. . . . . . 9
Parasitology . . . . 10
Hemoglobin Types of Sheep. . . 11/


Basic Design and Management Practices. 19
Resistance of Sheep to Haemonchus
contortus . . . . . .. 22
Immunology and Hematology ... 22
Parasitology. . . . . . 24
Hemoglobin Types of Sheep. . . .. 25

IESULTS . . . . . . . . . 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 HIaemonchus
contortus . . . . . ... 43
Immunology and Hematology . .. 43
Parasitology. . . . ... .. 44
Hemoglobin Types of Sheep. . . . 46

SUMIARY ... . . . . . . . .... 50

LITEiRATURE CITED. . . . ... . .. 52



Table Page

Jl. Gene Frequency of Hb A in Some Breeds
of Sheep. . . . . . . . . 13

2. Experimental Design: Number of Ewes per
Resistance Group. . .. ... .. 19

J3. 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 Volume 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


Table pag

14. The Relationship Between Hemoglobin
Type and Reproductive Performance
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


Internal parasite infections are a major source of

economic 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


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 Haemonchus contortus

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, Hartin 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 drugs 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 Hansom (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 Rambouillet sheep in a report by Loggins, Swanson

and Koger (1965). The Florida Native sheep is a cross-

breed which has developed through natural selection, under

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.


Life Cycle and Pathogenesis of Haemonchus contortus

The nematode H. contortus is a parasite of sheep

which normally inhabits the abomasum. 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 (Sommerville, 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


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. con-

tortus was purely hemorrhagic in character, since he was

able to reproduce the same blood picture in healthy lambs

by periodic bleeding from thejugular vein.

Resistance of Sheep to Haemonchus contortus


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. Sheep which had expelled an infection of

H[. 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 edematous 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 II. contortus larvae previously remained

flaccid and normal when massive doses of exsheathed larvae

were injected into the abomasum (Stewart, 1955). In

lambs hypersensitized by previous infections with II.

contortus, the abomasum 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 HI. 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 usually 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 challenge 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 (Weir et al., 1948; Richard et

al., 1954 a; and Richard et al., 1954 b ) 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

B12 in the rumen in response to the severe drain of blood

by H. contortus.


Anemia is one of the clinical symptoms associated

with haemonchosis in sheep. Georgi and Whitlock (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

31 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

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 Rambouillet



Christie et al. (1964 c) presented ova count data

which suggested that host resistance 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, Xingsbury (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 populations in lambs protected by previous

H. contortus infections than in uninfected controls fol-

lowing a challenge dose of H. contortus infective larvae.

Loggins et al. (1965) reported lower worm counts in Florida

Native sheep than in Rambouillet 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

tetramer. 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;

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 Ub B,


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 (Moore 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


Gene Frequency of Hb A in
Some Breeds of Sheep

Gene Location
Frequency of
Breed of Hb A Flock Reference







Romney Marsh

Romney Marsh













Great Britain

Great Britain

Great Britain

Great Britain



Great Britain




Evans et al,

Evans et al..

Evans et al.,

Evans et al.,

Evans et al.,

Evans et al.,

Evans and
Blunt 1961

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


Two other hemoglobin types have also been detected

in sheep, which are under special conditions.

Harris and Warren (1955) identified the hemoglobin

of normal 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 electrophoretic 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 migration, Hb C was probably the same as Hb N.

Braend and Efremov (1965) found small amounts 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. Efremov and Braend (1966) found that

Hb N occurred in relatively higher amounts in lambs than

in adults, with one-month-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 B 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 lib N

is closely linked to one of the structural genes con-

trolling ib 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

(Mounib 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 wre 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,

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-

nificantly, although there was some suggestion that

hemoglobin heterozygotes produced a slightly larger

number of lambs. Evans and Turner (1965) reported that

ewes with Bb 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

born 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.


Basic Design and Management Practices

The basic design was a 2 X 2 factorial, with two

foundations (120 Florida Native ewes and 60 Rambouillet

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.


Experimental Design
Number 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-

manent Coastal Bernmudagrass 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 inadequate.

Anthelmintic treatments were initially eliminated

from all groups to allow genetic resistance potential

to be manifested. As a result, death losses increased

in the Rambouiilet 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 Rambouillet


Ewes were culled on age and failure to fit into the

resistance group for whih they were selected. Natural

selection, manifested 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 we're placed with the ewe

flock after the breeding season to challenge them with

natural infections of H. contortus. Mean hemoglobin

level from weaning to 18-months of age was used to deter-

mine the resistance group into which a replacement ewe was


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 IIb 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


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-


Hemoglobin Type of Sires for
1967 Breeding Season

Hemoglobin Group
Breed Number Type to Which Mated

Florida Native N20 AB Low

N21 B Low

N80 A High

N81 AB High

N82 'AB Spare

Rambouillet R01 B Low

R02 AB High

R80 B Low

plete year (December, 1966, to November, 1967). When

a ewe from the sample flock died, it was replaced by

a comparable ewe from the same breed-resistance group.

Resistance of Sheep to Haemonchus contortus

Immunology and Hematology

Blood samples were collected from the entire sheep

flock at two-month intervals from an ear vein. Blood

samples were collected into heparinized capillary tubes

and hemoglobin pipettes.

A microtechniy- 3 using heparinized capillary tubes

was employed for packed cell volume determination. Each

tube was filled with blood, sealed at one end with

plastic clay and centrifuged at 11,500 rpm for five
minutes in a Model MB centrifuge. At the completion

of the cycle, the tubes were placed in a microcapillary
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
spectrophotometer at a wave-length of 525 millimicrons

and converted into grams of hemoglobin per 100 ml. of


At one-month intervals, .wo 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. VacutainerR

tube containing ethylenediaminetetraacetic acid (EDTA) as

an anticoagulant and a second sample was collected into a

10 ml. Vacutainer tube containing no anticoagulant, to

1International Equipment Company, Needham Hts.,


Bausch and Lomb Spectronic 20.

obtain serum. In the laboratory, packed cell volumes and

hemoglobin levels were determined by the methods described


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 centrifuging 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 transmission of the solution was
measured in a spectrophotometer at a wavelength of 540

millimicrons and converted into grams gamma globulin per

100 mL .f serum.

Para sitology

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 (Whitlock, 1948).

Since mixed, natural parasitic infections were used,

1Bausch and Lomb Spectronic 20.

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, 1949) and identified as to species (Skerman and

Hillard, 1966).

Abomasal worm counts were obtained from most of the

sheep which died and from 20 Florida Native ewes culed

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. aliquots of the abo-

masal contents and washings were counted and multiplied

by the appropriate factor to obtain total worm counts.

Hemoglobin Tynes 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 flock using the same technique.

The red blood cells were washed with 0.S5 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 Smithies (1955) was used for hemo-

globin type determinations in this study. A 0.06 M Tris-

EDTA-borate buffer with a pH of 9.0 (12.1 grams Tris,

0.9 grams boric acid, 1.6 grams Na2 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 pH of 8.6 (24.7 grams sodium

barbital, 3.4 grams diethylbarbituric acid and distilled

water to bring buffer volume to 1200 ml.) was used as

the electrode buffer. The power supply was 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 between hemoglobin types.


Resistance of Sheep to Haemonchus Contortus

The deviations in the number of ewes per breed-

resistance group are shown in Table 4. Death losses


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

Florida Native Rambouillet
Dates Hi L igh Low High Low

Number of ewes

August, 1966 60 60 31 31
October, 1966* 60 60 26 30
February, 1967 58 59 22 29
April, 1967 56 57 19 28

ewes added 4 4 3 5

June, 1957 59 58 21 29
August, 1967* 59 58 15 34
October, 1967 59 58 15 27
February, 1968 59 58 14 24

Death losses

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

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 Rambouillet

ewes had survived without anthelmintic treatment.

Immunology and Hematology

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 volumes and hemoglobin levels similar to

these for the whole flock were 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


Mean Packed Cell Volumes and
Hemoglobin Levels of the Ewe Flock

Florida Native Rambouillet
Dates High Low High Low

Packed cell volume (%)

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./100 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


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 (%)
December 28.4 25.8 22.8 20.4
January 26.6 22.3 21.8 15.5
February 28.4 24.9 22.5 15.3
March 27.3 24.7 20.8 20.1
April 26.7 22.8 22.3 21.6
May 27.2 24.4 24.7 21.9
June 27.4 24.2 23.8 22.1
July 27.9 25.2 30.7 24.6
August 28.8 27.6 29.8 23.8
September 28.4 26.3 28.5 24.2
October 31.5 27.5 28.7 24.6
November 31.8 26.6 28.8 22.7

Hemoglobin level (g./100 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./100 ml.)
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
March 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 1.18 1.39

globulins and hemoglobin levels.


Mean H. contortus ova counts, taken in July and

September, 1966, to determine the effectiveness of

selection, are shown in Table 7.' While large breed


Helminth Ova Counts from Ewe Flock*

Florida Native Rambouillet
High Low High Low

Mean ova per
gram of feces
July, 1966 93 .42 534 577
September, 1966 80 163 1288 3310

Percent samples
with less than
200 ova per
gram of feces 92.5 91.7 53.8 36.7

Percent samples
with more than
1,000 ova per
gram of feces 2.5 1.7 21.2 41.7

* 2'94% 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

about two percent of the Florida Native ewes had counts

of more than 1000 ova per gram of feces. The Rambouillet

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 group had lower

ova counts than the low resistance group. A significant,

negative relationship (-0.32, P<0.01) 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 stomachs 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


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


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

Florida Native Rambouillet
Month High Low High Low

Ova per gram feoes

December 1680 3070 6920 6220
January 2070 2710 6920 8660
February 167 344 9525 6400
March 50 511 3800 400
April 70 430 400 1467
May 40 390 1467 3175
June 388 588 900 1660
July 70 356 167 350
August 60 310 50 317
September 67 457 33 283
October 70 256 300 471
November 475 370 1000 960

Larval cultures (% Haemonchus contortus)

December 100 99 99 98
January 96 95 98 99
February 97 100 100 100
March 95 98 100 95
April 98 94 99 100
May 96 93 85 93
June 92 96 92 97
July 92 86 95 95
August 86 94 96 98
September 83 79 97 95
October 94 88 100 75
November 92 91 97 99

*7'94%/ H. contortus


Necropsy Haemonchus contortus Counts
On Ewes Ihbich Died and Culled Ewes

Florida Native llambouillet
High Low High Low

Ewes which died

Number sampled 5 5 10 9
Mean H. contortus
counts 10880 12500 12230 11311

Culled ewes

January, 1968
Number sampled 4 4
Mean H. contortus
counts 5 4

February, 1968*
Number sampled 6 6
Mean H. contortus
counts 283 550

*'Many immature 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 levelsof 3.8 and 4.4 grams percent) but

had only 1400 and 2100 H. contortus, respectively, at

necropsy. While these were the two highest counts, they

were considerably lower than the counts from ewes which

had died.

Hemoglobin Types of Sheep

Hemoglobin types were determined on blood samples

from the 30 sample ewes (Table 10). A greater incidence


Hemoglobin Types of
"Sample Flock" by Resistance Groups

Resistance Hemoglobin Type
Breed Group A AB B ABC

Florida Native High 2 7 1 -

Low 3 3 4 -

Rambouillet High 1 3 1

Low 1 4 -

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 Rambouillet 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

' 7


the shortest distance from the origin and the lib B

fraction migrated the intermediate distance from the


Samples 1 and 10, from six-month old Florida Native

lambs, were Hb AB. 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 Rambouillet 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. The 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 Rambouillet 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 assumption was made that ewes which live to

this age must have some resistance and, therefore, the low


Hemoglobin Type of
Ewe Flock by Resistance Groups

Resistance Hemoglobin Type
Breed Group A AB B AC ABC

Florida Native High 21 24 11 -
(less than 9-years
of age) Low 14 14 18 -

Florida Native High 2 1 -
(9-, 10- and 11-
years of age) Low 8 3 3 1 -

gene frequency for Hb A 0.558

Rambouillet High 6 9 1

Low 12 22 -

gene frequency for Hb A 0.190

hemoglobin percent 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 lib 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

Table 12. Hemoglobin type had a highly significant

effect on hemoglobin level and packed cell volume. Ewes


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

Hemoglobin Cell Weight of
Source d.f. Level Volume Ewes

Total 701

Hb type (T) 2 21.14** 396.41** 338.53

Season (S) 5 65.29** 287.86** 9185.64**

T x S 10 1.72* 6.17 36.55

Animal (A) 116

A:T 114 3.46** 48.01** 412.06**

AS:T 570 .75 6.35 32.09



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 lib Ab were small.

The effect of hemoglobin type cn' 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-


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

Sample month Hemoglobin Type

Hemoglobin level (g./lO0 ml.)

February 7.50 7.08 7.02
April 8.60 8.04 7.59
June 7.92 8.05 7.49
August 8.84 8.90 8.07
October 7.29 7.56 6.98
December 6.60 6.79 6.15

Average 7.79 7.74 7.22

Packed cell volume (%)

February 29.7 28.2 27.4
April 28.6 27.4 25.4
June 28.1 27.5 25.7
August 31.0 30.8 28.3
October 31.9 32.0 29.1
December 29.5 29.1 27.2

Average 29.8 29.2 27.2

Weight of the ewes (pounds)

February 89.5 92.1 92.3
April 79.3 80.6 80.7
June 81.7 83.0 82.9
August 85.9 88.8 87.5
October 90.9 94.0 90.8
December 104.6 107.0 103.1

Average 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 mean square for animal X season within hemoglobin

type (AS:T). The ratios of these two variances were

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


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

Performance Lamb Hemoglobin Type
of ewes Crop A AB B

barren ewes (o) 1967 4.8 7.3 3.3'

1968 20.9 26.2 25.8

Total 12.9 16.9 14.7

single lamb (%) 1967 83.3 75.6 70.0

1968 69.8 64.3 61.3

Total 76.5 69.9 65.6

twin lambs (%) 1967 11.9 17,1 26.7

1968 9.3 9.5 12.9

Total 10.6 13.2 19.7

(4C 2

twin births than ewes with Hb A, although Chi squared

analysis did not show the difference to be significant.

Ewes with lib 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


Least squares constants of 70-day weights of Florida

Native lambs are shown in Table 15. Type of birth had a


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


70-day Weight

Variable 70-day Weight

General Mean

type of
the lamb

Hb A


Hb B







Type of Birth**

single lambs

twin lambs



Hemoglobin type of the dams

Hb A -0.03

Hb AB 1.34

Hb B -1.31

*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 pounds 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.



Resistance of Sheep to Haemonchus contortus

Death loss in the Rambouillet ewes was higher than

in the Florida Native ewes even though many of the Ram-

bouillet ewes were drenched with phenothiazine and none

of the Florida Native ewes were drenched. Fourteen Ram-

bouillet 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. Holman (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

different in their adaptability to Florida conditions.

The Florida Native breed was developed by natural

selection under Florida production conditions (Jilek,

1966). 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

gamma 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.


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 (1065),

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-

ship. Ewes with low ova counts did not necessarily have

high hemoglobin 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 H. contortus). This

would indicate that necropsy count on ewes 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 ewes. 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 number of worms in the ewes just

prior to the sacrificing of the ewes in January. The

number of immature worms present in the ewes sacrificed

in February would indicate that 'elf-cure"had occurred

and new infections were developing.

Hemoglobin Types of Sheep

"Self-cure," a dynamic cyclic phenomenon, influences

the hematological and parasitological values of a sheep.

If resistance is measured by one of these parameters, the

level of resistance will be influenced by the particular

phase cf the "self-cure" cycle of the animal. An animal

sampled just prior to expulsion of the worms may there-

fore appear to have very little resistance toH. 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 hematological measurements will be

high and parasitological measurements will be low.

One solution to this problem is to select a discrete

variable which is correlated with 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 changesin an animal's adult hemoglobin type

have involved the production of lib C in very anemic sheep

having lib A (Blunt 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

animal when the sample is obtained will not influence

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. While 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 adverse conditions than under less adverse

conditions. Adaptation to Florida production conditions

would include increased resistance to H. contortus in-


The analyses of resistance group differences within

the Florida Native breed and of the effect ac hemoglobin

type on hemat iogical values indicate, likewise, that

sheep with HIb A are more resistant to parasites than

sheep with Hb 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 II. 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 to 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- 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 th;an la:- s born as singles

(Shelton and Carpenter, 1957). .While the individual lambs

from Hb B ewes weighed less, there were more of them to
increase the production per ewe bred over the Hb A and AB

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 Raambouillet 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

II. contortus infections.

Death loss was greater in the Rambouillet than in

the Florida Native ewes. 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. This 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

H. contortus.

The mean necropsy worm count on ewes which died was

11,690 II. contortus. Breed differences for necropsy

counts on ewes which died were small. The mean necropsy

worm count on culled Florida Native ewes was only 250

H. 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 Hb A gene was observed in

the Florida Native breed and in the high resistance groups

than in the Rambouillet breed and low resistance groups,

respectively. Resistance group differences within the

Florida Native breed approached significance at the ive

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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Anthony Francis Jilek was born July 11, 1942, in

Barron County, Wisconsin. 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 B a member of Alpha Zeta, Kappa Delta Pi, and the

American Society of Animal Science.

This dissertation was 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

Dean, College of Agriculture

Dean, Graduate School

Supervisory C imittee:

ha6 i rima/ n/

L7 ih ^. r rniaM

2 7^

-- Z )axT-e^ i ,'

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