Reproductive Parameters of Dorper Ewes: Implications for An

REPRODUCTIVE PARAMETERS OF DORPER EWES: IMPLICATIONS FOR AN

ACCELERATED LAMBING SYSTEM IN SOUTH TEXAS

A Thesis

VICTOR V. FLORES

Submitted to the College of Graduate Studies

Texas A&M University-Kingsville

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

August 2018

Major Subject: Animal Science

ABSTRACT

Reproductive Parameters of Dorper Ewes: Implications for an Accelerated Lambing System in

South Texas

(August 2018)

Victor V. Flores, B.S., Texas Tech University

Chairman of Advisory Committee: Dr. Randy L. Stanko

There has been considerable change in the U.S sheep industry since the introduction of hair sheep, most notably, the Dorper breed of sheep. A decline in wool profitability has led to a significant expansion of Dorper sheep throughout the US with the highest inventory in Texas.

Dorper sheep naturally shed, demand lower labor costs, and are suitable for a hot, arid environment. Additionally, Dorpers produce a high-quality carcass making them suitable for

American lamb markets. An accelerated lambing system establishes a breeding and lambing schedule which produces three lamb crops every two years. Successful implementation of an accelerated lambing system requires ewes to have a short post-partum anestrus period and be capable of breeding at all times of the year. We hypothesize that the annual reproductive parameters of Dorper ewes and ewe lambs are sufficient for implementation of an accelerated lambing system in South Texas. In study #1, the age and BW of early, mid, and late winter-born ewe lambs was determined. Late winter-born ewe lambs were younger and lighter (P<0.05) in

BW at puberty than early winter-born ewe lambs. Ewe lambs began to attain puberty in August, and 89% were pubertal by December. All ewe lambs were anestrus by March. In study #2, fall- born ewe lambs (n=18) were exposed to a fertile ram or ram plus progesterone treatment during the non-breeding season. One ewe lamb reached puberty, conceived, and gave birth to twin lambs. Remaining ewe lambs (n=17) were exposed to a ram 60-d later, during the normal breeding season. These fall-born lambs had a 94% conception rate and a 126% lamb crop. In

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study #3 multiparous ewes that were either long-, mid-, or short-term postpartum were introduced to a fertile ram during the non-breeding season. Pregnancy rates and lambing percentage were lowest in short post-partum ewes (P<0.05). Regardless of days postpartum pregnancy rate (83%), percent ewes cycling (87%), and lamb crop (124%) was acceptable. The findings of these studies demonstrate the various reproductive characteristics of Dorper ewes indicating, with careful management, suitability for the implementation of an accelerated lambing system by sheep producers in South Texas.

ACKNOWLEDGMENTS

First, I would like to thank my graduate advisor, Dr. Randy Stanko, for his extensive personal and professional guidance throughout my graduate career and for allowing me to work alongside him in research. The lessons I learned from working as a TA in your courses will continue to impact me, serving as a reference of what excellence in teaching should be.

I would also like to thank Dr. Michelle Garcia for teaching me invaluable lessons on scientific research. I truly enjoyed working as a TA under your leadership and taking courses which constantly challenged me to be a better student.

I would also like to thank Dr. Natasha Bell, thank you for continuously supporting me, encouraging me, and for always making time for my seemingly constant writing edits.

Thank you to all my friends and colleagues, Juan Martinez, Gustavo Faz, Travis Rocha,

Javier Martinez, and Daisy Trevino, who helped me in conducting research and making my time in Kingsville a great experience.

DEDICATION

This thesis is dedicated to my family, my parents, Cornelio and Angela Flores and my brothers, J.J., Ricky, and Jose Luis, who were my constant source of support and motivation; this accomplishment would not have been possible without them.

TABLE OF CONTENTS Page

ABSTRACT…………………………………………………………………………………..….iii AKNOWLEDGEMENTS…………………………………………………………………...…....v DEDICATION……………………………………………………………………………………vi TABLE OF CONTENTS .………………………………………………………………..……..vii LIST OF TABLES.………………..………………………………………………………..….....ix LIST OF FIGURES…..……………………………………………………………………..…….x CHAPTER I. INTRODUCTION………………………………………………………..………...1 CHAPTER II. LITERATURE REVIEW ………………………………………….……………..2 Reproduction in the Ewe……………………..…………………………………………..………..2 Reproductive management………………………………………………………..….……2 Puberty……………………………………………………………….…………………………....4 Photoperiod effects…….…….……………………………………………………..……..4 Weight and age effects……………………………………………………………….…...5 Early Breeding of Ewe Lambs………………………………………………………………….....6 Spring-born……...……………………………………………………………...... 6 Fall-born………………………………………………………………………...... 7 Postpartum Breeding………….……………………………………………………………..…….7 Suckling effects.……….…………………………………………………………...……...8 Nutrition effects…….……………………………………………………………...……...9 Ram effect……….………………………………………………………………...……...9 Origin of Dorper Sheep……………………………………………………….……………….....10 Breed characteristics……………....……………………………………………....……..11 Reproductive Characteristics of Dorper Sheep………...……………………………….…..……12 Puberty……………………………………………………………………………..…….12 Estrous cycle………………………………………………………………………...…...12 Synchronization of Estrus…………….………………………………………………….13 Conception rate….……………………………………………………………………….13 Lambing percent…………………………………………………………………………16 Lamb survival……………………………………………………………………………16

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Summary…………..………..…………………………………………………...……….17 CHAPTER III. AGE AND WEIGHT OF EARLY, MID, AND LATE WINTER-BORN DORPER EWE LAMBS AT PUBERTY………...…………………………………………...... 18 Introduction………….……………..…………………………………………………….18 Materials and Methods ………………………………...... 19 Results and Discussion……………………………………………………………..…....21 CHAPTER IV. EFFECT OF RAM INTRODUCTION ALONE OR WITH CIDR PRE- TREATMENT ON INDUCTION OF PUBERTY IN FALL-BORN DORPER EWE LAMBS DURING THE NON-BREEDING SEASON ….……………………………...……..….……...24 Introduction……………………………………………………………………...……….24 Materials and Methods………………………………………………………..……...…..25 Results and Discussion……………………………………………………………...…...28 CHAPTER V. REPRODUCTIVE PERFORMANCE OF DORPER EWES WITH VARYING DAYS POST-PARTUM TO RAM INTRODUCTION IN THE NON-BREEDING SEASON………………………………………………………………………………………....30 Introduction…………………………………………………………..……….………….30 Materials and Methods………………………………………………………...…………31 Results and Discussion………………………………………………………………...... 34 CHAPTER VI. IMPLICATIONS…………..…………………………………………….……...36 REFERENCES…………………………………………………………………………………..37 VITA……………………………………………………………………………………………..42

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LIST OF TABLES

Page

Table 1. Breeding seasons under an accelerated lambing system…………………………….…15

Table 2. Initial mean age and weight and at puberty of winter ewe lambs...... 22

Table 3. Reproductive performance of fall born ewe lambs …………………….………………29

Table 4. Reproductive performance of Dorper ewes with varying days postpartum ……….…..35

LIST OF FIGURES

Page

Figure 1A. Cumulative percentage puberty and cycling of winter born lambs………………....23

Figure 1B. Onset of puberty and subsequent estrous cycles of all ewe lambs…………………..23

CHAPTER I

INTRODUCTION

Accelerated lambing is a viable production practice for increasing profitability in market lamb production. Implementing an accelerated lambing system can optimize profits by managing ewes to potentially produce 3 lamb crops in 2 years, versus one lamb crop per year. This management practice may prove to be sustainable in South Texas; however, a hot, humid climate adds an additional challenge. Generally, wool breeds of sheep follow a strict seasonal breeding pattern and are not well suited for hot climates. This favors the use of hair sheep in tropical and sub-tropical environments, which have lower input costs, i.e. no shearing and greater heat tolerance. In Texas, the most popular hair-type breed of sheep is the Dorper breed. Dorpers produce early maturing, fast growing lambs, with high quality carcasses which make them ideal for U.S. lamb markets and are a good candidate for an accelerated lambing system. Ewe must have the capability for non-seasonal reproduction and a short postpartum anestrous period.

Additionally, selection of ewe lambs that experience puberty at an earlier age can be advantageous, producing more lambs in a lifetime. Careful management of ewes and ewe lambs may allow for a viable accelerated lambing system to be used, increasing efficiency and profitability for sheep producers in South Texas.

CHAPTER II

LITERATURE REVIEW

Reproduction in the Ewe

Reproduction in the ewe can be divided into two distinct seasons: the normal breeding season and the anestrus season. The normal breeding season involves regular estrous cycles

(mean=17 days) each with an estrus period (mean=30 h) and subsequent ovulation. The anestrus season is characterized by absence of estrous cycles, due to gestation, postpartum period and seasonally during increased day-length (Rosa and Bryant, 2003). Under natural conditions, most sheep are seasonally polyestrous in the fall and winter when day-light is decreasing, until mid-

December, and typically lamb in the spring when day-light is increasing. Different breeds of sheep are restricted to either a short or long breeding season depending on their degree of seasonal reproduction (Ortavant et al., 1988). Other factors affecting reproduction in the ewe are nutrition, body weight, lactation, latitudes, altitudes, environmental temperature, presence of the male (“ram effect”), and the season of birth (Rosa and Bryant, 2003). Appropriate management of ewes is imperative in order to control and optimize reproductive efficiency.

Reproductive management

The use of reproductive management tools gives producers an added advantage and can be used for the synchronization of estrus, which in turn provides a shorter breeding and lambing season. With an increase in lamb uniformity (weight & age) there is the possibility of increasing profits. The use of progestogens, and exogenous hormones PGF2α, GnRH, and eCG are viable options for the synchronization of estrus in ewes.

Administration of exogenous progesterone via sponges, oral ingestion, or implants has been well documented as a method to synchronize estrus of ewes. Presently, the most widely used insert is the controlled internal drug release, (EAZI-BREED™ CIDR ®) an intravaginal

insert made of silicone and impregnated with progesterone (Wheaton et al., 1993). The exogenous progesterone inhibits luteinizing hormone (LH) which is needed for ovulation

(Hansel et al., 1973). An external source of progesterone will extend the luteal phase of an estrous cycle. Typically, an LH surge is initiated approximately 38-72 h after removal, and subsequent ovulation occurs (Cleefe et al., 1998). This is useful in reproductive management of sheep in that producers can synchronize estrus in many ewes which can result in a short breeding and lambing period. Another method widely utilized in the livestock industry to control the estrous cycle is prostaglandin F2α (PGF2α) (Cleeff et al., 1998). Natural PGF2α destroys functioning corpora lutea (CL), reducing circulating progesterone (McCracken, 1971).

Administering PGF2α at the end of the luteal phase of the estrous cycle allows follicles to ovulate typically 40 h after a single intramuscular injection (Mekuriaw et al., 2015). An 87-100% success rate of synchronization of estrus has been reported using 5 d progestagen treatment followed by a single injection of PGF2α at progestagen removal (Beck et al., 1993; Titi et al.,

2008). Alternatively, giving two injections of PGF2α 10 d apart may produce a 79-100% estrus response in treated ewes (Allison and Kellly, 1978; Titi et al., 2008).

An alternative to the use of progestogens and PGF2α is gonadotrophins. Equine chorionic gonadotropin (eCG or PMSG) an analogue to follicle stimulating hormone (FSH) stimulates ovarian follicle growth (Ali, 2007). Several authors have reported treating ewes with eCG in doses of 200-400IU at time of or 2 d prior to progestagen impregnated sponge removal can cause

83-100% of ewes to exhibit an estrus response (Ali, 2007; Tekin et al., 1992; Rekik et al., 2002;

Quintero-elisea et al., 2011). Gonadotropin-releasing hormone (GnRH) is another reproductive hormone that can be used in ewes to improve reproductive efficiency. Endogenous release of

GnRH from the hypothalamus occurs in a pulsatile pattern and stimulates luteinizing hormone

(LH) and follicle-stimulation hormone (FSH) secretion from the pituitary gland (Cavalcanti et

al., 2012). A single treatment of GnRH following the removal of a progestagen can induce an LH ovulatory peak within 1-4 hours and reduce the time to ovulation in mature ewes (Eppleston et al., 1991). Additionally, GnRH administered immediately after artificial insemination increases the rate in the occurrence of multiple births (Türk et al., 2008).

Puberty

Photoperiod effects

A major deterministic factor for the onset of puberty in female sheep is photoperiod which varies naturally by season. A variety of experiments have reported that spring-born ewe lambs become pubertal at a younger age than fall-born ewe lambs. Foster (1981) conducted a study on fall and spring born Suffolk ewe lambs and the onset of puberty, with and without photoperiod manipulation. He reported that spring (March) and fall-born (October) ewe lambs raised under a natural photoperiod became pubertal at approximately 217 and 343 days of age, respectively. However, in fall-born ewe lambs exposed to the day-length of spring born lambs beginning at 4 wk of age reached puberty by 245 days of age, approximately 98 days earlier than fall-born lambs reared under natural photoperiod (Foster, 1981).

Yellon and Foster (1985) conducted a study to determine the influence of photoperiod conditions on puberty in ewe lambs using artificial photoperiod treatments from birth, or soon after. They reported that ewe lambs exposed to continuous long day (15L:9D) or short day

(9L:15D) photoperiod experienced onset of puberty beyond 1yr of age. Additionally, they exposed ewe lambs to 10 wk (12-22 wk of age), 5 wk (17-22 wk of age), or only 1 wk (22 wk of age) of long day (15L:9D) photoperiod, followed by short day (9L:15D) photoperiod until puberty. The onset of puberty was in the normal age range of spring-born lambs (25-35 wk of age). These authors concluded that a period of long days followed by short days is crucial for ewe lambs to reach puberty (Yellon and Foster, 1985).

Fitzgerald and Butler (1982) studied the influence of season of birth on age at puberty in ewe lambs. They compared spring and summer born Dorset and Morlam ewe lambs. Age at puberty for spring and summer born lambs were 220±6 d and 153±7 d, respectively. Ewe lambs born in summer (2.5±0.3) had less (P<0.01) ovulatory cycles than spring (5.5±0.6) born ewe lambs. For all ewe lambs that ovulated, a minimum weight of 34 kg was obtained (21/26)

(Fitzgerald and Butler, 1982). Lambs born in August (14L:10D) were of sufficient weight

(Foster and Ryan, 1979) and experienced a sufficient (45-60 d) period of long days (Yellon and

Foster, 1985) to reach puberty near the end of the normal breeding season when day-length was beginning to increase.

Weight and Age effects

One factor which contributes to the variation in age at puberty is body weight

(Dýrmundsson, 1981). Various studies have reported a minimum body weight must be achieved in order for ewe lambs to reach puberty (≥30 kg, Foster and Ryan, 1979; ≥33 kg, Foster, 1981;

≥34 kg, Fitzgerald and Butler, 1982). In most cases, ewe lambs must reach 50-70% of their mature body weight before becoming pubertal (Dýrmundsson and Lees, 1972). Generally, faster growing and heavier ewe lambs reach puberty earlier than slower growing ewe lambs (Quirke,

1979).

Suttie et al. (1991) conducted a study to determine if ewe lambs maintained at a specific body weight would affect the onset of puberty during the normal breeding season (decreasing day-length). Coopworth ewe lambs (10 wk old) were divided into one of six treatment groups:

(A) ad libitum feed (n=6), (B) fed ad libitum to 28 kg and maintained at 28 kg, (C) fed ad libitum to 24 kg and maintained at 24 kg (n=6), (D) maintained at a body weight of 20 kg up to wk 29 then fed ad libitum (n=6), (E) maintained at 20 kg and infused with insulin from 29-31 wk of age

(n=5) and (F) maintained at 20 kg (n=6). Ad libitum fed lambs reached puberty at a mean age of

26.1±1.8 wk and mean BW of 44.2±2.4 kg. Approximately 5 weeks later 5/6 ewes in Group B reached puberty (31.6 ±1.3 wk and 28 kg). Lambs in Group D reached puberty (4/6) at 33.9±0.6 wk and 27.9±0.7 kg which was 5 wk after starting an ad libitum diet; no ewe lambs reached puberty in Groups C, E, and F by 38 wk of age (Suitte et al., 1991). Lambs that were maintained below threshold weight for puberty become pubertal after receiving an ad libitum diet. This observation suggests an influx of nutrients after nutrient restriction potentiated onset of puberty in fed-restricted lambs’ reproductive activity.

Early Breeding of Ewe Lambs

Breeding sheep at an early age (< 1 yr), lambing as yearlings, will minimize the time from birth to first lambing and in turn decrease early input costs. Moreover, ewes that produce a lamb as yearlings will have greater lifetime production. This increase in reproductive efficiency and diminished input costs can increase overall profits.

Spring-born

Ewe lambs born in the spring become pubertal at an earlier age as compared to fall-born ewe lambs. These lambs will be of sufficient age and BW for the commencement of puberty and reproductive performance during the typical breeding season (decreasing day-length).

Dýrmundsson and Lees (1972) conducted a 2 yr study on age at puberty in spring-born Clun

Forest ewe lambs. In yr 1, spring-born ewe lambs (n=33) were introduced to a ram in the subsequent fall and these ewe lambs exhibited first estrus at 228.3±2.4 d and mean BW of

36.3±0.9 kg. These ewe lambs had a lambing rate (lambs/ewe) of 113%. In yr 2, spring-born ewe lambs (n=84) were introduced to a ram in the subsequent fall and attained puberty at mean age of 223.7±3.0 d and mean body weight of 32.2±0.5 kg (Dýrmundsson and Lees, 1972). The age and BW at puberty of spring-born ewe lambs (born during increasing d length) occurs during the normal, short day, breeding season.

Fall-born

Fall-born ewe lambs are of sufficient age and BW for the onset of puberty, equal to spring-born lambs, during the non-breeding season (increasing day-length). This delays puberty and poses a challenge in early breeding. Knights et al. (2002) conducted a study comparing exogenous hormone treatment and ram effect on the induction of estrus and ovulation of fall- born ewe lambs (mixed breeds) during the non-breeding season (15L:9D). Fall-born ewe lambs were randomly assigned to one of five treatment groups: (C) control lambs, no treatment (n=7),

(R) lambs introduced to ram only (n=7), (P) lambs received a progesterone insert for 5 d (n=5),

(PR) lambs received a 5 d progesterone insert and exposed to a ram (n=11), (PER) similar to PR and treated with estradiol benzoate 1 d after ram introduction (n=11). No control or progesterone only treated lambs displayed estrus or ovulated. Only lambs that had ram exposure ovulated (R;

85.7%, PER; 71.4%, PR; 33.3%); however, ram only lambs failed to exhibit estrus. Percentage of lambs exhibiting estrus and ovulating were less (P<0.05) for PR than PER treatment, 45.5 vs

81.8 and 33.3 vs 71.4, respectively. It was concluded that ram exposure was sufficient to cause ovulation; however, without progesterone pre-treatment lambs failed to exhibit estrus. Moreover, estrogen was needed to stimulate a significant percentage of ewe lambs to exhibit estrus and ovulate during the non-breeding season (Knights et al., 2002).

Post-partum Breeding

One method of increasing reproductive efficiency in sheep is establishing a shorter postpartum period [parturition to subsequent conception]. Three factors that can influence the postpartum interval to estrus and ovulation are suckling, nutrition, and the presence of a ram as a stimulus (Hunter and Lishman, 1967).

Suckling effects

There appears to be conflicting evidence in the literature concerning the effects of suckling on resumption of estrus and ovulation in sheep. Fletcher (1971) reported the effect of suckling on post-partum ovulation and estrus in ewes that lambed during the normal breeding season (fall). Pregnant Merino ewes placed in one of four groups; (a) normally reared lambs (b) restricted suckling to (3 1-h periods/d) (c) lamb removed after birth (d) lamb removed after birth with 5 IU. of oxytocin injected 10 x /d for the first 17-d post-partum. There was no difference in d from parturition to first estrus between groups that had lambs removed (44.7 ±2.7 d), had restricted suckling (49.5 ±2.4 d), or normally reared lambs (47.8 ±2.1 d). Restall and Starr

(1977) reported similar results with Merino ewes lambing in the winter (10L:14D) or spring

(14L:10D). Ewes were either suckled for 40 d or had lambs removed at birth. More ewes ovulated that had lambs removed (72% vs 40%) but both groups had a similar mean time (25 d vs 24 d) to first ovulation (Restall and Starr, 1977). Barker and Wiggins (1964) reported on the effect of lactation on postpartum interval using fall-lambing, Rambouillet ewes (n=244) in a two- year study. In yr-1, the average postpartum interval to estrus for ewes that did not suckle their lambs (57.7 d P<0.05) was shorter (than ewes with a single (72.1 d) or twin lambs (86.6 d);

~90% of all ewes were cycling within 120 d. Similar results were reported the second yr with mean postpartum interval to estrus for non-suckled ewes (54.9 d) being shorter (P<0.05) than ewes with twins (88.1 d) or single lamb (88.4 d). Kann and Martinet (1975) reported the effects of complete denervation of mammary tissue to inhibit the neural reflex arc initiated by suckling and its influence on the duration of post-partum anestrus. Five Prealpes du Sud ewes were surgically denervated and were without any nervous connections from mammary tissue. Control ewes (n=8) were not altered and both groups of ewes were allowed to suckle their lambs. Control ewes ovulated between 25-50 d postpartum with less than 50% (3/8) exhibiting estrus. All

surgically denervated ewes exhibited estrus and ovulated within 50 d postpartum with 3/8 ovulating within 14 d postpartum (Kann and Martinet, 1975). In summary suckling may be inhibitory to the resumption of reproductive capability, an additional factor extending the postpartum interval.

Nutrition effects

Direct nutritional effects on postpartum length are inconclusive (Dunn and Kaltenbach,

1980). Hunter and Van Aarde (1971) reported the effects of nutrition on resumption of sexual activity of Merino ewes lambing throughout the year. Ewes were fed at rates of 110% or 60% of the estimated daily NRC requirements for both lactating and non-lactating ewes. Ewes which lambed in July and were kept on a high plane of nutrition had their first ovulation post-partum earlier (P<0.05, 48.2 d) than similar ewes fed a low plane of nutrition (88.5 d); however, they observed considerable variation in estrus response (Dunn and Kaltenbach, 1980). For all other lambing months studied (November, March/April) no significant differences in postpartum interval to ovulation due to diets were noted. Lishman et al. (1974) reported similar observations in a six-year study using Merino ewes (n=761) lambing in autumn and were fed either 100% or

50% of NRC requirements. Similar postpartum interval to estrus was reported for ewes on a low

(mean = 49 d) or high (mean = 47 d) plane of nutrition (Lishman et al., 1974). During the normal breeding season nutrition may not be a critical factor affecting days to estrus postpartum.

Ram effect

Godfrey et al. (1998) reported the effect of ram exposure on the postpartum interval of St.

Croix ewes. The study consisted of ewes lambing during two different, yet similar, day lengths,

July (13.2 h) and November (11.2 h). Ewes were allocated into two treatment groups: 1) ram exposure starting 7 days postpartum (n=22) or 2) isolated from rams through d 63 postpartum

(n=24). These authors reported that ewes which were exposed to rams had a shorter (P<0.05)

postpartum interval to ovulation compared to ewes isolated from rams after November (32.2 ±

3.1 d vs 41 ± 2.9 d) or July lambing (32.7 ± 3.9 vs 43.5 ± 3.7 d). Furthermore, ram exposed ewes displaying a normal estrous cycle following lambing had higher pooled serum progesterone concentrations than non-exposed ewes, (3.3 ± .4 ng/mL vs 2.3 ± .3 ng/mL, respectively; Godfrey et al., 1998). Hunter et al. (1970) reported on the effects of lactation and ram exposure in Border

Leicester × Merino ewes lambing in different seasons. Ewes were assigned to either ram exposure from 30 d postpartum or no ram exposure. Half in each treatment group were allowed to suckle the lamb for 1 d while the remaining ewes suckled the lamb for 40 d. During the non- breeding season ewes with ram exposure ovulated earlier (P<0.05) than non-exposed ewes (98.5 vs 187.2 d, respectively). Lactation had no effect on postpartum ovulation rates (Hunter et al.,

1970). Regardless of breeding season, exposure to a ram reduced the postpartum interval to first ovulation.

Origin of Dorper Sheep

During the early 1930’s, a majority of South African lambs exported to London were rejected due to poor carcass quality. Carcass rejection was largely attributed to genetics of indigenous fat-tail sheep, which produced a carcass that did not meet British market standards.

By the early 1940’s a project was imitated under the direction of the Department of Agriculture of South Africa (DASA) to create a new breed of sheep that would reduce the incidence of carcass rejection by British markets (American Dorper Sheep Breeders’ Society, 2013). This new breed of sheep would be developed to produce hardy, fast growing lambs reared in arid environmental conditions with good quality carcasses, and able to be extensively managed at low production costs. Therefore, researchers began crossing purebred rams of different British sheep with indigenous fat-tail sheep (Milne, 2000). Out of many crosses, the most successful led to

development of the Dorper breed which was the mating of Blackhead Persian (indigenous fat-tail sheep) ewes to Dorset Horned rams.

The earliest accounts of the Dorset Horn sheep date back centuries in England where it thrived as an all-purpose breed (The American Livestock Breeds Conservancy). Several factors led to the decision of using Dorset Horn sheep as the sire for the development of the Dorper breed. Mainly because Dorsets produce lambs with excellent carcass quality, being heavily muscled with uniform fat distribution. As well, Dorset Horn sheep have a tendency for multiple births and high milk production which leads to fast growing lambs (Nel, 1993). These traits complemented those of the Blackhead Persian making the Dorper breed of sheep a success.

The Blackhead Persian breed of sheep originated from the arid regions of present day

Somalia (Mason, 1988). They are a fat-tail, hair sheep breed with a black head and white body.

Blackhead Persian sheep are noted for having shorter anestrous periods and post-partum intervals to estrus (Joubert, 1962). The combination of an extended breeding season, the ability to thrive in harsh conditions, and the lack of wool for added heat tolerance made the Blackhead Persian an exceptional choice in creating the Dorper breed of sheep.

Breed Characteristics

Dorper sheep are regarded as an early maturing sheep breed, achieving excellent growth rates under harsh environmental conditions (Cloete et al., 2000). They are heavily muscled sheep that produce high quality carcasses at slaughter (Snowder and Duckett, 2003). Dorper sheep should be symmetrical and well-proportioned, with a long, deep, and wide body with well- muscled shoulders and hindquarters. The BW of Dorper ewes at 2 years of age range from 50 kg to 70 kg (Cloete and de Villiers, 1987; Manyuchi et al., 1991). Wool covering should not be excessive. Ideally they should have a mix of kemp and wool over the top of the back while having a clean underline free of kemp (American Dorper Sheep Breeders’ Society, 2013). Two

color variations exist: white bodied sheep with a black head are Dorpers whereas solid white sheep are called White Dorpers. Both color variations follow the same breed standards (Milne,

2000). Both White Dorpers and Dorpers are recognized for having long breeding seasons, good conception rates and lambing percentage (Joubert, 1962; Schoeman and Burger, 1992; Van

Niekerk, 2000)

Reproductive Characteristics of Dorper Sheep

Puberty

Ewe lambs that reach puberty at an early age have the potential for an increase in overall lifetime lamb production. Joubert (1962) reported Dorset x Blackhead Persian (early Dorper) ewe lambs (n=108) became pubertal at an average age of 399 d ranging from 195-872 d. More recently, Schoeman et al. (1993) reported Dorper ewes reached puberty at 8.14 ± 0.29 mo

(approximately 244 d) of age with mean BW of 50.8 ± 1.82 kg. These observations were similar to Greeff et al. (1993) whom reported Dorper ewe lambs having their first estrus at approximately 7 mo age and mean BW of 39 ± 2.7 kg. Collectively, these findings support the conclusion that Dorper ewes can become pubertal earlier than many wool-type sheep breeds.

This could be attributed to selective breeding of early maturing animals.

Estrous cycle

Reports on estrous cycle length in Dorper ewes have remained consistent across many studies. In an early study, (Joubert, 1962) mean estrous cycle length of Dorset Horn X Blackhead

Persian F1 (Dorpers) ewes was 16.9 d with a range of 12 to 25 d while the mean length of estrus was 33.3 h with a range of 24 to 43.4 h. Elias et al. (1985) analyzed reproductive characteristics in multiparous (n=17) and primiparous (n=9) Dorper ewes imported into Israel. Multiparous ewes had an estrous cycle of 17.6 ± 1.1 d (vs 16.6 ± 1.2 d) and exhibited estrus for 36 ± 8 h (vs

28 ± 6 h) compared to primiparous ewes.

Synchronization of Estrus

Estrus synchronization protocols are designed to allow for shorter breeding and lambing seasons with increased lamb uniformity. These protocols are especially useful during the non- breeding season when high conception rates may be difficult to achieve. Although estrus synchronization protocols have been established in wool type breeds of sheep, there is a lack of information on estrous synchronization of Dorper ewes. Martinez-Tinajero et al. (2011) conducted a study in Southern Mexico (14°50’N, 92°11W) to determine the response of Dorper ewes synchronized with various hormone treatments during the non-breeding season. Ewes were randomly assigned to one of three treatment groups. Ewes (T1; n=20) were introduced to a ram without hormone treatment (control) or received administration of an intravaginal sponge impregnated with a progestagen analog (medroxyprogesterone acetate) for 12 d followed by an injection of 500 IU of equine chorionic gonadotropin (eCG) and then introduced to rams (T2; n=15). The third treatment group (T3; n=16) received an initial injection of 100 μg of GnRH (d

0) followed by a PGF2α injection 5 d later and a second injection of GnRH at d 6.5. The percentage (P<0.05) of estrus response for treatments T1, T2, and T3, were 65%, 93.3%, and

25%, respectively. Ram introduction to estrus was longer (P<0.05) in T1 (70.6±33.03 h) compared to T2 (39.8±13.6 h). Pretreating ewes with a progestagen analog for 12 d followed by administration of eCG and ram introduction efficiently synchronized estrus, making it a viable synchronization protocol for Dorper sheep (Martinez-Tinajero et al., 2011).

Conception rate

Conception rate, defined as ewes that lambed per ewe mated, is a crucial measure of a successful and effective sheep breeding system. Researchers have reported variation in conception rate of Dorper ewes. Elias et al. (1985) conducted a study on Dorper ewes (n=17) under an accelerated lambing system. Ewes were joined with rams for three 5 wk periods at

various mo (Table 1.). Mature ewes had a first estrus conception rate of 84.3% across all three mating periods with lowest occurring in Jul-Aug (70.6%) and highest in Apr-May (94.1%).

Overall conception rate for primiparous ewes (n=9) bred in Oct-Nov was 77.8% with 66.7% conceiving at first estrus (Elias et al., 1985). Cloete and de Villiers (1987) found similar results in a commercial flock of Dorper ewes (n=813, 2 - 7+ yr old) raised under extensive management.

Over all ages, mean conception rate was 89% with little difference across age groups (Cloete and de Villiers, 1987). Snyman and Olivier (2002) studied the reproductive performance of first parity or mature Dorper ewes with distinct phenotypes, strictly hair or with wool covering, raised under extensive conditions in South Africa (30°59’S, 22°09’E). They reported no difference in conception rate between hair type (n=872; 85.9%) and wool type (n=874; 82.5%) mature ewes.

Conception rate of first parity ewes was lower than mature ewes but there was no difference between hair type (n=237; 67.1%) or wool type (n=245; 63.3%) of Dorpers (Snyman and

Olivier, 2002). More recently, Gavojdian et al. (2015) reported the mean conception rate of

White Dorpers was 86.7% and Dorpers was 81% during the normal breeding season. Variation in conception rates reported in the literature would suggest season of breeding (transition of daylight) as a considerable factor affecting reproduction.

Table 1. Breeding seasons under an accelerated lambing system

Breeding Period Dates Photoperiod (L:D) Season

1 7 Apr.-14 May 13:11 Late Spring/early Summer

2 7 Nov.-14 Dec. 10:14 Winter

3 7-Jul.-14 Aug. 14:10 Summer

Primiparious Ewes 7 Oct.-14 Nov. 11:13 Fall

Adapted from Elias et al. (1985), Beer-Sheva, Israel

Lambing Percent

Sheep are not a litter bearing species; however, they have the ability to produce multiple offspring which is economically advantageous when total pounds of lamb produced per ewe is considered. Elias (1985) calculated lambing percentage of three 5 wk mating periods (previously described). Lambing percent to Apr-May breeding was 152.9% and 129.4% following August and December breeding. Primiparous ewes bred in the fall had a lambing percent of 122.2%

(Elias et al., 1985). Van Niekerk (2000) conducted a large study on the reproductive performance of Dorper ewes (n=2,239) implemented into a system of five unique mating seasons per year. The average lambing percent over the five mating seasons was 102%, with a low of

77% and high of 125% (Van Niekerk, 2000). Schoeman and Burger (1992) found similar results and reported Dorper ewes (n=699) had a mean lambing of 121% over a 6-yr study. The variation in lambing percent may be due to seasonal effects on reproductive activity of ewes.

Lamb Survival

Lamb survival from birth to weaning plays a crucial role in profitability. A ewes mothering ability, in addition to lamb health and vigor, are factors that influence lamb survival.

Cloete and de Villiers (1987) reported on 2 to 7+ yr old Dorper ewes having an overall mean lambing survival rate of 91%, with a range of 89% to 94%. Regardless of birth type, single or twin, 91% of lambs survived to weaning. Schoeman and Burger (1992) found similar lamb survival rate of 94% over a six yr period, while Snyman and Oliver (2002) reported 96% for mature ewes and 94% for first parity ewes. Overall, lamb survival for Dorper sheep is relatively high under various environmental and management conditions.

Summary

There has been considerable change in U.S. lamb markets due to lower wool demand, and decreased profit opportunities from wool. Many sheep producers have shifted their focus to producing lambs for meat production. Acceptable carcass quality and no need for wool shearing have increased the popularity of hair breeds of sheep in U.S. sheep flocks. The predominant hair sheep breed is the Dorper, introduced in the early 1990’s. Popularity of the breed has been enhanced, in part by the adaptability to harsh environments and lower management requirements.

Reproductive traits of Dorper sheep may make them suitable candidates for the implementation of an accelerated lambing system; a management system which is designed to produce three lamb crops in two years by a majority of ewes. Three research trials on the reproductive parameters of Dorper ewes were conducted to determine the potential for their use in an accelerated lambing system by sheep producers in South Texas.

CHAPTER III

AGE AND WEIGHT OF EARLY, MID, AND LATE WINTER-BORN DORPER EWE

LAMBS AT PUBERTY

Introduction

Dorper sheep were imported into the United States less than 25 years ago and have caused a significant change in lamb markets. Not requiring shearing and producing lambs with excellent carcass quality has led to numerous sheep producers replacing wool flocks of sheep with Dorper sheep. In Texas, the popularity of hair sheep has created premiums at lamb markets in recent years. The use of an accelerated lambing system makes it possible for an increase in total lamb production and number of lambs ready for market on an annual basis. Ewe lambs which become pubertal at a younger age can be incorporated into an accelerated lambing system with flexibility and will potentially produce more lambs over a lifetime. However, age at puberty is influenced by several factors including BW and the effects of photoperiod at birth and during the pre-pubertal growing period. There have been various studies confirming that season of birth affects the age at which ewe lambs become pubertal. Spring-born ewe lambs are at a younger age and a lighter BW when commencement of puberty occurs compared to fall-born ewe lambs

(Foster, 1981). However, there are few studies on puberty of Dorper sheep in the United States.

My hypothesis is late winter born ewe lambs will become pubertal at a younger age and lighter body weight than early and mid-winter born lambs. The objective of this study was to determine the effects of natural photoperiod on age and BW of early, mid, and late winter-born Dorper ewe lambs at puberty.

Materials and Methods

The Institutional Animal Care and Use Committee (IACUC) at Texas A&M University-

Kingsville (TAMUK) approved all animal procedures in this study. All studies were conducted at the TAMUK Research Farm located at 27°32' N. Latitude and 97°52' W. Longitude with an elevation of 17.9 meters above sea level.

Animals

Pre-pubertal ewe lambs (n=18) were observed over an 8-mo period to determine onset of puberty and the timing of their first anestrous period. Observations began in August for early winter (n=6; 222.8±2.6 d, 37.7±1.6 kg), winter (n=6; 173.6±6.9 d, 30.9±1 kg), and late winter- born (n=6; 151±3.5 d, 26±1.3 kg) ewe lambs. Mean date of birth for each group was December

27th, February 11th, and March 5th, respectively.

Feeding

Ewe lambs were fed daily 2% of their body weight (DM basis) a commercial protein

(20% CP) pellet (Sheep and Goat 20; Lyssy & Eckel Feeds©, Poth, TX) with ad libitum access to hay of various quality (7 - 10% CP). Commercial pellets were fed to lambs using 3 bunk feeders (2.4 m, “V” Grain Trough; Sydell, Burbank, SD) to ensure an equal space for all lambs.

Fresh water, trace minerals and a salt block were provided ad libitum.

Experimental Procedure

Weekly blood samples were collected beginning at 7-mo of age (August 9th, 2016) until confirmation of first anestrus for all ewes (March 28th, 2017). During the observation period, BW and a body condition score (BCS; scale 1 to 5) was recorded approximately every 30 days.

Serum progesterone concentration was used to determine onset of puberty. Puberty was defined as two consecutive weekly blood samples with serum progesterone concentration >1ng/mL

followed by a low serum progesterone concentration <1ng/mL and a serum progesterone pattern indicative of a normal estrous cycle.

Blood Collection

Blood was collected from the jugular vein using 20GX1” drawing needles (Greiner Bio-

One, Monroe, NC) and 10 mL serum collection tubes (Vacutainer®, Becton Dickinson, Franklin

Lakes, NJ). Samples were immediately put on ice then refrigerated for (4°C) for 4 hours.

Following refrigeration, all blood samples were allowed to warm to room temperature for 1h then centrifuged at 1800 x g for 20 min at 4°C. Serum was harvested and placed into a 1.7 mL micro-centrifuge tube (VWR® Microcentrifuge tubes, VWR International, Radnor, PA) and stored at -80°C until progesterone analysis.

Progesterone Analysis

Serum progesterone concentration was analyzed using a radioimmunoassay kit

(ImmuChem ™; MP Diagnostics, Santa Ana, CA). Incubation time for serum samples was 4 h with radiolabeled (125I) progesterone in tubes coated with progesterone antibodies. Assay tubes were inverted leaving only serum progesterone and radioactively labeled progesterone bound to the tube. Amount of radiation emitted from tubes was then analyzed by a gamma counter which used a progesterone standard curve for comparison. Inter- and intra-assay coefficients of variation were 8% and 10%, respectively.

Statistical Analysis

Analysis of variance was used to compare independent variable, season of birth (early winter, mid- winter, late winter) on initial age and weight, and age and weight at puberty using PROC

FREQ ANOVA procedure of SAS (Statistical Analysis System version 9.4 for Windows; SAS

Institute, Cary, NC, USA).

Results and Discussion

Late winter-born ewe lambs were pubertal at an earlier (P<0.05) age and lighter BW than early winter-born ewe lambs with mid-winter born lambs being intermediate and similar

(P>0.05) to both (Table 2.). Cumulative percentage pubertal of all ewe lambs was 22% in

August, 50% in September, 67% in October, 89% in November, and by December 94% (Figure

1B.). One late winter-born ewe lamb, consistently the lightest in BW, failed to reach puberty during the first 12 mo. In February, one early winter-born ewe lamb remained estrous cycling but by March all ewe lambs were anestrus (Figure 1A. and B.). Lambs had a mean ADG of 0.1 ±

0.01 kg from August to December and a mean BW of 40.7±1.3 kg at the end of December.

Foster (1981) reported a similar age (217 d) at puberty for spring-born ewe lambs under natural photoperiod as we report for late winter-born Dorper ewe lambs (Table 2.). The mean BW of all ewe lambs at puberty was above 30 kg, the threshold weight reported by several researchers for attainment of puberty (Foster and Ryan, 1979; Foster, 1981; Fitzgerald and Butler, 1982). The additional ~70 d and ~10 kg obtained by early winter born ewe lambs vs late winter born ewe lambs initiated puberty earlier while extending estrous cycles.

Table 2. Mean (± SEM) initial age and weight, and age and weight at puberty of early, mid, and late winter-born Dorper ewe lambs

Season of birth Initial ageⱡ Initial BW (kg)ⱡ Age at puberty BW at puberty (kg)

Early winter 222.8±2.6a 37.7±1.6a 256.8±7.3a 40±1.0a

Mid-winter 173.6±6.9b 30.9±1.0b 245±8.5a,b 37.1±2.1a,b

Late winter 151.6±3.5c 26.7±1.3c 223.6±12.6b 33±1.7b

a, b, c Column means with different superscripts differ significantly at P<0.05

ⱡAge and BW at initiation of study, differ (P<0.05) by design

100% 90% 80% 70% 60% Cycling Early winter-born 50% Mid-winter-born 40% Late winter-born 30% 20%

10% Cumulative Cumulative % andPuberty Cycling 0% Aug Sep Oct Nov Dec Jan Feb

Figure 1A. Cumulative percentage puberty and subsequent estrous cycles of early-winter, mid- winter, and late winter-born ewe lambs.

Figure 1B. Onset of puberty and subsequent estrous cycles of all ewe lambs.

CHAPTER IV

EFFECT OF RAM INTRODUCTION ALONE OR WITH CIDR PRE-TREATMENT ON

INDUCTION OF PUBERTY IN FALL-BORN DORPER EWE LAMBS DURING THE

NON-BREEDING SEASON

Introduction

Ewe lambs that reach puberty at an early age have the potential to conceive earlier and reduce costs associated with maintenance from birth to initial breeding. Additionally, the early breeding of ewe lambs has been reported having no negative effects in ewe longevity (Kenyon et al., 2011). Fall born ewe lambs are typically held over, past the age and BW of spring-born lambs at puberty, until the subsequent fall breeding season. However, sheep producers can use reproductive tools to potentially overcome the challenge from seasonal photoperiod. One commonly used tool is an exogenous hormone, progesterone, which blocks estrus and ovulation when administered to cycling ewes until its withdrawal (Carlson et al., 1989). As well, ram introduction alone has been reported to induce ovulation in ewe lambs during the non-breeding season (Knights et al., 2001). Fall-born ewe lambs with sufficient BW can be bred early, during the non-breeding season with pretreatment of progesterone followed by ram introduction.

Therefore, it was my hypothesized that fall-born ewe lambs of sufficient age and body weight can be induced into puberty, during the non-breeding season, with progesterone pretreatment followed by ram introduction. The objective of this study was to determine the influence of ram introduction on onset of puberty of fall born Dorper ewe lambs during the non-breeding season

(long days; 14L:10D) with or without the use of progesterone pre-treatment.

Materials and Methods

The Institutional Animal Care and Use Committee (IACUC) at Texas A&M University-

Kingsville (TAMUK) approved all animal procedures in this study. All studies were conducted at the TAMUK research farm located at 27°32' N. Latitude and 97°52' W. Longitude with an elevation of 17.9 meters above sea level.

Animals and Feeding

Dorper ewe lambs (n=18) that were born from Oct. 10 to 31st (L11.2:D12.4) were used.

At the initiation of the study (June 13th) lambs had a mean age of 230.3 ± 1.5 d and a mean BW of 40.4 ± 2.9 kg. Ewe lambs received no ram exposure prior to the study. Ewe lambs were fed daily 2.5% of their BW (DM basis) a commercial protein (20% CP) pellet (Sheep and Goat 20;

Lyssy & Eckel Feeds©, Poth, TX) with ad libitum access to hay of various quality (7 - 10% CP).

Commercial pellets were fed to lambs using 2 bunk feeders (2.4 m, “V” Grain Trough; Sydell,

Burbank, SD) to ensure an equal space for all lambs. Fresh water, trace minerals and a salt block were provided ad libitum.

Initial Ewe Lamb Breeding

Ewe lambs were blocked by BW and then randomly assigned to control with only ram introduction (C; n=9, 237.5±2.1 d, 40.4 ± 4.1 kg), or progesterone pre-treatment for 7-d followed by ram introduction (PR; n=9, 237.8±1.9 d, 40.4 ± 4.3 kg). The PR treatment ewes received a

CIDR® (EAZI-BREED ™ CIDR®; Zoetis, Parsippany, NJ) containing 0.3 g of progesterone.

Treatment groups were housed separately during the breeding period, June 13th to July 1st (18 d,

14L:10D). Average daily temperature, high and low, was 34.4°C and 23°C, respectively.

Second Breeding Period

Remaining non-bred ewe lambs (n=17/19, 314.8 ± 1.5 d, 52 ± 3.5 kg) from first breeding study period were used and housed together. Ewes were joined with a fertile Dorper ram for 31 days, from August 30th to September 30th (31 d, 12L:12D). Average daily temperature, high and low, was 33.3°C and 21.6°C, respectively. No blood samples were taken during the breeding period. Real time ultrasound was used 50 days after ram removal to confirm pregnancy. A single ewe lamb, confirmed pregnant, was lost one month before the start of the lambing period due to a vaginal prolapse.

Blood Collection

Weekly blood samples were taken starting two weeks prior to start of treatment, during, and two weeks after the end of the study. Real time ultrasound was used 45 days after removal of ram to confirm pregnancy. Blood was collected from the jugular vein using 20GX1” drawing needles (Greiner Bio-One, Monroe, NC) and 10 mL serum collection tubes (Vacutainer®,

Becton Dickinson, Franklin Lakes, NJ). Samples were immediately put on ice then refrigerated for (4°C) for 4 h. Following refrigeration all blood samples were allowed to warm to room temperature for 1h then centrifuged at 1800 x g for 20 min at 4°C. Serum was harvested and placed into a 1.7 mL micro-centrifuge tube (VWR® Microcentrifuge tubes, VWR International,

Radnor, PA) and stored at -80°C until progesterone analysis.

Progesterone Analysis

Serum progesterone concentration was analyzed using a radioimmunoassay kit

bound to the tube. Amount of radiation emitted from tubes was then analyzed by a gamma counter which used a progesterone standard curve for comparison. Inter- and intra-assay coefficients of variation were 8% and 10%, respectively.

Statistical Analysis

Due to the outcome of the study and the rejection of our hypothesis no statistical analysis was performed.

Results and Discussion

A single control ewe lamb (1/18, 5.5%) became pubertal and successfully conceived during the initial breeding period (June 13- July 1) and gave birth to twin lambs (November).

Introduction of ram with or without pretreatment with progesterone failed to induce puberty in fall-born ewe lambs during the non-breeding season. This contrasts results reported by Knights et al. (2002) where fall-born ewe lambs of similar age and BW were introduced to a ram with and without progesterone pretreatment during the non-breeding season. In that study ewe lambs introduced to a ram only, failed to exhibit estrus, however 85.7% ovulated. When pretreated with progesterone then introduced to a ram, 45.5% of ewe lambs exhibited estrus and 33.3% ovulated

(Knights et al., 2002). In the current study ewe lambs with or without progesterone pretreatment exposed to a fertile ram failed to become pubertal during the non-breeding season. Apparently photoperiod dominated the reproductive endocrine system and the presence of a ram stimulus.

Future studies using exogenous hormones, such as PMSG, in addition to progesterone pretreatment and ram introduction may help overcome challenges with photoperiod during the non-breeding season.

During the second breeding period (September), remaining non-bred ewes had a conception rate of 94% and mean lamb crop per ewe of 1.25 was achieved. The mean ram to lamb interval was 165.7±1.7 d and lambing to first service was similar to second service, 46.6% vs 53.3%, respectively (Table 2). At the start of the second breeding period, ewe lambs had a mean age of 314.8 ± 1.5 d, similar to the age at puberty (306.5±4.9 d) for fall- born Dorper ewe lambs reported by Taylor et al. (2016). Wiggins et al. (1970) reported a mean age at puberty of

316 d in fall-born Rambouillet crossbred ewe lambs while Foster (1981) reported an average age of puberty of 343 d in fall-born Suffolk ewe lambs.

Table 3. Reproductive performance of Dorper ewe lambs in the second breeding period

Conception rate (%) 94.40 (16/17) Ram to lamb interval (d)a 165.7 ± 1.8 Mean day of birthing (d)b 14 ± 2.4 Lambs per ewe 1.25 ± 0.1 Lambing to 1st servicec 46.60% Lambing to 2nd serviced 53.30% Number of ewes twinning 4 Number of ewes with singles 11 Mean birth weight (kg) 4.3 ± 0.4 aDay from ram introduction to mean date of lambing bMean day of birthing , day of first lamb born = day 1 cPercent lambs born during first half of the lambing period dPercent lambs born during the second half of the lambing period

CHAPTER V

REPRODUCTIVE PERFORMANCE OF DORPER EWES WITH VARYING DAYS

POST-PARTUM TO RAM INTRODUCTION IN THE NON-BREEDING SEASON

Introduction

Hair sheep have become increasingly popular in the U.S. due to lack of a profitable market price for wool and the ability to produce superior market lambs. In Texas the most popular hair type breed of sheep is the Dorper. Various breed characteristics make the Dorper breed of sheep an excellent candidate for implementation of an accelerated lambing system in subtropical environments.

In order to implement a successful accelerated lambing system, producing 3 lamb crops in 2 years, resumption of reproductive activity postpartum must be achieved relatively quickly.

Breeding postpartum ewes during the non-breeding season combined with recent lactation can be a challenge. The use of a ram, “ram effect” has been documented as a viable management practice to induce estrus and ovulation in ewes during the non-breeding season (Godfrey et al.,

1998). Therefore, I hypothesize multiparous Dorper ewes with a postpartum period greater than

100 days will successfully respond to the ram effect during the non-breeding season. The objective of this study was to compare the reproductive performance of Dorper ewes of various days postpartum introduced to a fertile ram during the non-breeding season (13L:11D).

Materials and Methods

The Institutional Animal Care and Use Committee (IACUC) at Texas A&M University-

Animals

Mature 2+ yr-old multiparous Dorper ewes (n=28) were used. Treatment groups were established according to days since previous lambing, defined as the date of previous lambing to date of introduction to ram. The three treatment groups were classified by post-partum interval length as either short (SPP; n=10, 100 ± 2.7 days), mid (MPP; n=11, 130 ± .68 days) or long

(LPP; n=7, >200 days). Weaning of lambs from previous parturition for SPP and MPP ewes occurred at a mean of 62 ± 3.2 and 67 ± .6 days, respectively. Body condition score (BCS, scale

1 to 5) of ewes ranged from a score of 2.5 to 3.5. Ewes had no ram exposure since the previous breeding period (>8 mo).

Feeding

Ewes were fed daily 2% of their body weight (DM basis) a commercial protein (20% CP) pellet (Sheep and Goat 20; Lyssy & Eckel Feeds©, Poth, TX) with ad libitum access to hay of various quality (7 - 10% CP). Commercial pellets were fed to lambs using 3 bunk feeders (2.4 m, “V” Grain Trough; Sydell, Burbank, SD) to ensure an equal space for all ewes. Fresh water, trace minerals, and a salt block were provided ad libitum.

Non-seasonal Breeding

Ewes were joined with a ram for 30 d. during the non-breeding season. From May 1st to the 31st (13L:11D), average high and low temperature was 31.9°C and 20.6°C, respectively.

Blood Collection

Weekly blood samples were collected beginning two weeks prior to start of the treatment and continued until one week after the end of the study. Analysis of progesterone was used to find ewes that ovulated before, during, and after the breeding period. Real time ultrasound was used 45 days after ram removal to confirm pregnancy. Blood was collected from the jugular vein using 20GX1” drawing needles (Greiner Bio-One, Monroe, NC) and 10 mL serum collection tubes (Vacutainer®, Becton Dickinson, Franklin Lakes, NJ). Samples were immediately put on ice then refrigerated for (4°C) for 4 h. Following refrigeration all blood samples were allowed to warm to room temperature for 1h then centrifuged at 1800 x g for 20 min at 4°C. Serum was harvested and placed into a 1.7 mL micro-centrifuge tube (VWR® Microcentrifuge tubes, VWR

International, Radnor, PA) and stored at -80°C until progesterone analysis.

Progesterone Analysis

Serum progesterone concentration was analyzed using a radioimmunoassay kit

(ImmuChem ™; MP Diagnostics, Santa Ana, CA). Incubation time for serum samples was 4 h with radiolabeled (125I) progesterone in tubes coated with progesterone antibodies. Assay tubes were inverted leaving only serum progesterone and radioactively labeled progesterone that was bound to the tube. Amount of radiation emitted from tubes was then analyzed by a gamma counter which used a progesterone standard curve for comparison. Inter- and intra-assay coefficients of variation were 8% and 10%, respectively.

Statistical Analysis

Pregnancy rates and postpartum intervals were evaluated by Chi-Square using the PROC

FREQ procedure of SAS (Statistical Analysis System version 9.4 for Windows; SAS Institute,

Cary, NC, USA). Additionally, analysis of variance (ANOVA) was used comparing independent variables of days postpartum (LPP, MPP, SPP) on dependent variables conception rate (pregnant

ewes/ewes exposed), lambing rate (lambs/ewes lambing) and lambing percent (lambs/ewes exposed).

Results and Discussion

Short post-partum ewes had a lower (P<0.05) pregnancy rate and lower (P<0.01) lambing percent compared to MPP ewes (Table 3.) Difference in conception rate between SPP and LPP was similar to SPP vs MPP but due to a small n, level of statistical significance was not as great.

Regardless of days post-partum, pregnancy rate (83%), total percent ewes cycling (87%), and lamb crop (124%) was acceptable (Table 3.). Similar findings were reported by Hunter et al.

(1970) where ewes that were exposed to rams, ovulated and average of 98.5 d postpartum.

Barker and Wiggins (1964) reported 90% of postpartum ewes resumed estrus cycles by 120 d postpartum. Based on the current study more than 130 d postpartum prior to ram introduction may be necessary if a maximum number of ewes are to conceive. The effect of lactation may carryover beyond weaning (60 d) and up to 100 d postpartum. In addition, these SPP ewes were

≤ 3.0 BCS at ram introduction. Conversely, ewes that had not produced a lamb in over 200 d, had a higher BCS >3.0, Adequate management of BW before the subsequent breeding period is crucial to produce higher conception rates and incidence of twins. Increasing photoperiod observed during the non-breeding season did not appear to dominate the ram as a stimulus, in the current study. However, there is a need for further studies conducted during other months (Jan-

Mar) of the year.

Table 4. Reproductive performance of Dorper ewes with varying days postpartum during the non- breeding season

SPP MPP LPP Overall n 10 11 7 28

Conception rate (%)a 60 100 100 87

Lambing percentage (%)b 80 172 142 131

Lambing rate (%)c 133 172 142 149

Ram to lamb interval (d)d 171.6±3.4 169.4±1.8 172±1.6 170.7±1.2

Ewes with a single lamb 4 3 4 11

Ewes with twin lambs 2 8 3 13

Average lamb BW (kg) 4.27 3.62 3.26 3.66 a(Ewes pregnant/ewes exposed) x 100; SPP vs MPP, P=.056; SPP vs LPP P<0.05; LPP vs MPP, NS b(Lambs born/ewes exposed) x 100; SPP vs MPP, P<0.01; SPP vs LPP, P=0.08; LPP vs MPP, NS c(Lambs born/ewes lambing) x 100; SPP vs MPP, NS; SPP vs LPP, NS; LPP vs MPP, NS dDay from ram introduction to mean date of lambing

CHAPTER VI

IMPLICATIONS

An accelerated lambing system is designed to produce more lambs per ewe per yr.

However, with an additional lambing period, birth month of ewe lambs may occur outside of typical spring and early summer lambing. Therefore, Dorper ewe lambs may require careful management, with particular attention to age, BW, and date of birth if destined for an accelerated lambing system. For incorporation into an accelerated lambing system it is recommended that replacement ewe lambs need to have BW ≥ 30 kg and > 200 d of age. Ewe lambs born during winter can potentially enter a breeding period from August to January. Ewe lambs born in the fall, however, may need further reproductive management if they are to enter a breeding period during the non-breeding season. In addition to progesterone pretreatment, additional exogenous hormone such as eCG (equine chorionic gonadotropin) may be required prior to ram introduction. We believe this type of protocol may be a viable option to obtain high conception rates from fall born ewe lambs during the non-breeding season.

Multiparous ewes that are 100 to 130 d postpartum exposed to fertile ram during the non- breeding season will successfully (>60%) resume reproductive activity. However, proper management of BCS postpartum and prior to ram introduction is crucial; 3.0 BCS being ideal.

Overall, Dorper ewes and ewe lambs achieved adequate conception rates (87-94%) and lamb crop percentage (126-131%) when bred at different times of the year. The findings in these studies suggest Dorper sheep are an acceptable hair breed for implementation of an accelerated lambing system by sheep producers in South Texas.

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VITA

Victor V. Flores was born and raised in small farm in Laredo, Texas. Following high school,

Victor attended Laredo Community College where he received an associate degree in science in

2012. In 2014, he received his Bachelor of Science in animal science from Texas Tech

University. He was accepted to Texas A&M University-Kingsville (TAMUK) in the fall of 2015, working on his Master of Science in animal science under the supervision of Dr. Randy Stanko.

After graduating from TAMUK in 2018, Victor plans to continue his education in the field of reproductive physiology pursuing a Ph.D. at New Mexico State University.