REPRODUCTIVE PERFORMANCE OF SUFFOLK AND SUFFOLK-CROSS EWES AND EWE LAMBS EXPOSED TO VASECTOMIZED RAMS BEFORE BREEDING 1

REPRODUCTIVE PERFORMANCE OF SUFFOLK AND SUFFOLK-CROSS EWES AND EWE LAMBS EXPOSED TO VASECTOMIZED RAMS BEFORE BREEDING 1 R. E. Hudgens 2, T. G. Martin, M. A. Diekman and S. L. Waller a Purdue University 4, West Lafayette, IN 4797 ABSTRACT Multiparous Suffolk and Suffolk-cross ewes were randomly allotted to treatments within breed and year to measure effects of ram exposure, during transition from anestrus to breeding activity, on reproductive performance. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (DC), 2) ewes maintained across a net wire fence from two vasectomized rams for 15 d before breeding (FC) and 3) ewes maintained approximately 4 m away from rams (NC). At the end of the 15 d, all ewes were placed in one pasture and mated to three fertile Suffolk rams during a 34-d breeding season. A total of 96 Suffolk and 177 Suffolkcross ewes was utilized during the 3-yr experiment. A greater (P<.5) prebreeding ovulation percentage was observed in DC and FC than in NC ewes. Mating and lambing occurred approximately 6 d earlier for DC or FC ewes than for NC ewes. A similarly designed experiment was conducted using Suffolk and Suffolk-cross ewe lambs allotted to treatments within breed and year to measure effects of ram exposure during the natural breeding season, but prior to breeding. Treatment differences were not detected (P>.5) for date of first observed estrus, date of lambing, percentage of ewes lambing in the first 17 d of the lambing season, number of lambs born per ewe lamb exposed or number of lambs born per ewe lamb giving birth. (Key Words: Reproduction, Suffolk Ewes, Lambs, Mating.) Introduction Ram exposure has resulted in induced ovulation in anestrus ewes provided they had been conditioned by a period of isolation from rams (Schinckel, 1954; Oldham et al., 1978). Ram stimulation has been shown to overcome the inhibitory actions of estradiol-17/3 during anestrus (Martin et al., 1983), thus increasing the frequency of serum luteinizing hormone pulses, which culminates in ovulation within 6 I Journal paper no. 1159, Purdue Univ. Agric. Exp. Sta. Address reprint requests to this author. 3Present address: Dept. of Anita. Sci., Univ. of Idaho, Moscow 83843. 4 Dept. of Anlm. Sci. Appreciation is expressed to Dr. G. D. Niswender, Colorado State Univ., for supplying antisera to progesterone. We also thank G. R. Kelly, N. T. Kelly and R. A. Yoder for their assistance with data collection and M. E. Einstein for assistance with statistical analysis. Funded in part by a gift from the Indiana Sheep Breeders Assoc. Received February 19, 1987. Accepted June 12, 1987. d after introduction of rams (Knight et al., 1978; Martin et al., 198, 1983; Poindron et al., 198). The effect is mediated primarily by a pheromone secreted by the sudoriferous glands in the skin of the ram (Knight and Lynch, 198). Marshall (193) discussed differences among breeds in the degree to which ewes are anestrus. Merino ewes responded more readily than Romney ewes, which ovulated only if the rams were introduced near the end of anestrus (Edgar and Bilkey, 1963). Dyrmundsson and Lees (1972) reported that introduction of rams to Clun Forest ewe lambs during transition from non-breeding to breeding activity resulted in a high degree of synchronization at mating. However, information on the ram effect as a means of increasing percentage of ewe Iambs giving birth is not available. Two experiments were conducted to examine the reproductive performance of 1) Suffolk and Suffolk-cross ewes after exposure to vasectomized rams during transition from anestrus to breeding and 2) Suffolk and Suffolk-cross ewe lambs following exposure to vasectomized rams for 15 d during the natural breeding season. 1173 J. Anita. Sci: 1987. 65:1173-1179

1174 HUDGENS ET AL. Materials and Methods Exp. i. Purebred Suffolk and crossbred (1/2 Suffolk, 1/4 Rambouillet, 1/4 Finn) ewes were allotted randomly within breed to one of three treatment groups beginning August 6 in 1983, 1984 and 1985. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (direct contact=dc), 2) ewes maintained across a net wire fence from two mature vasectomized rams for 15 d before breeding (fence contact=fc) and 3) ewes maintained approximately 4 m away from rams (no contact=nc). A total of 96 multiparous Suffolk ewes and 177 multiparous crossbred ewes was utilized during the 3-yr experiment. Ewes were 2 to 8 yr of age and allotment to treatments was such that age did not influence either breed or treatment means. Ewes were maintained as one group on pasture 2 m or more away from rams for 3 mo before allotting them to treatments. After allotting ewes to treatments, the groups were placed in pastures of similar size. Forage in the pastures was primarily fescue (Festuca arundinacea) and Kentucky bluegrass (Poa pratensis). Twice weekly, blood samples were collected by jugular venipuncture from all Suffolk ewes each year, from a random sample of one-half the crossbred ewes in 1983 and 1984 and from all crossbred ewes in 1985. Five samples per ewe were collected beginning when sterile rams were placed with ewes and ending 15 d later (beginning of breeding). Serum was separated by centrifugation (2,3 X g for 2 min) and stored at -2 C. Serum concentrations of progesterone were quantified by radioimmunoassay (RIA) as described by Diekman and Hoagland (1983). The assay sensitivity for progesterone was.5 ng/ml. Intra-and inter-assay coefficients of variation were 11.5 and 14.2, respectively. Progesterone concentrations ~1 ng/ml were interpreted as an indication that ovulation had occurred and the ewe was having an estrous cycle. After a 15-d exposure to sterile rams (treatments 1 and 2) all ewes (including those not ovulating during sterile ram exposure) were combined in one pasture and were bred as a group to three fertile, mature Suffolk rams during a 34-d breeding period. Each ram was equipped with a ewe marking harness and marks were recorded daily. Body weights were recorded for each ewe at the beginning and end of the breeding season. Body condition was evaluated for each ewe at the beginning and end of the breeding season in 1984 and 1985. Body condition scores were assigned using a scoring system (MLC, 1983) of (very emaciated) to 5 (very fat; 3.5 = optimum condition). During the 34-d breeding season each year, all ewes were fed, as one group,.23 kg.head -1.d-1 whole shelled corn in addition to pasture. Ewes were managed as one group through gestation. At parturition, date of lambing, number of lambs born per ewe and number of ewes lambing were recorded. Exp. 2. In each of 3 yr Suffolk and crossbred (3/4 Suffolk, 1/8 RambouiUet, 1/8 Finn)ewe lambs were selected as replacements at approximately 9 d of age. A total of 58 Suffolk and 92 crossbred ewe lambs was utilized during the 3-yr experiment. Ewe lambs were placed in a birdsfoot trefoil (Lotus corniculatus) and bluegrass (Poa pratensis) pasture 2 m away from rams. The diet of these lambs was supplemented with.5 kg.head -1.d -1 whole shelled corn, and they were managed as one group until October 3, 1983, 1984 and 1985. At this time they were allotted randomly, within breed to one of the three treatments described in Exp. 1. The same pastures and vasectomized rams used for Exp. 1 were also utilized in this experiment. Supplementation with.5 kg. head-1, d-1 whole shelled corn was continued through breeding. Blood samples were collected by jugular venipuncture from all ewe lambs twice weekly. A total of five samples was collected from each lamb during a 15-d period just before breeding. Samples were handled and serum concentrations of progesterone were determined in these samples as in Exp. 1. Body weights were recorded for each ewe lamb at the beginning and end of the breeding season. Body condition scores were assigned at the beginning and end of breeding in 1984 and 1985 as described for Exp. 1. Ewe lambs were managed as one group through gestation and, number of lambs born, number of ewes lambing and lambing date were recorded at lambing. Statistical Analyses. All analyses were by the method of least-squares, fixed-model procedures (Harvey, 1977). Proportions of ewes that ovulated or lambed were estimated by including these as all-or-none dependent variables in the

EXPOSURE OF EWES TO RAMS BEFORE BREEDING 1175 data analyses (Harvey, 1982). The basic model included effects of breed, year, treatment and all two-factor interactions. Body weights of ewes and ewe lambs at the beginning (wt 1) and end (wt 2) of the breeding season were highly correlated (r=.96). Body condition scores at the beginning (CS1) and end (CS2) were moderately highly correlated (r=.56 to.63). Condition scores were correlated with weights (r=.53 to.68). Wt 1 was more highly correlated with the reproductive traits than wt 2, CS1 or CS2, and was included in the model as a covariate in both ewe and ewe lamb data sets. Results and Discussion Exp. 1. A greater (P<.5) percentage of ewes had ovulated before breeding if they had either DC or FC than if they had NC (table 1). A treatment x year interaction was not (P>.5) apparent for percentage of ewes ovulating before breeding, but year differences were observed. A lower (P<.5) percentage of ewes ovulated before breeding the first year (9.8 + 5.1) than in either the second (39.4 + 5.2) or third (31.2 + 4.7) year. Photoperiod is a major environmental cue influencing breeding activity in sheep (Yeates, 1949). However, it is unlikely that photoperiod was responsible for year differences in this experiment because introduction of fertile rams was on the same day of the year in each year of the experiment. Intensity of light or number of cloud-covered days has been shown to not influence breeding activity (Lees, 1971). Daily temperatures have been shown to influence the onset of breeding activity in the ewe (Lees, 1971; Robinson and Karsch, 1984). During the first year, percentage of ewes ovulating and percentage of ewes lambing in the first 17 d of the lambing season was lower than in either of the succeeding years. Mean daily ambient temperatures during the first 17 d of the breeding period were higher the first year than in either yr 2 or 3 (25.1, 2.3 or 21.3 C, respectively. Date of first estrus was earlier (P<.1) by approximately 6 d for ewes with DC or FC than for ewes with NC (table 1). This difference was also evident at lambing when ewes exposed to sterile rams (DC and FC) gave birth approximately 6 d earlier (P<.1) each year. A greater (P<.1) percentage of DC and FC than NC ewes gave birth during the first 17 d of the lambing season. This is in agreement with others who observed that scent from the ram was sufficient to produce a stimulating influence on ewes (Morgan et al., 1972; Knight and Lynch, 198). Joining Romney ewes with vasectomized Dorset rams for 14 d before breeding was shown to stimulate ewes to mate 1 to 5 d earlier than controls (Knight, 198; Knight et al., 198). A treatment x year interaction was observed (P<.1) for date of first estrus, date of lambing and percentage of ewes giving birth in the first 17 d of the lambing season. Therefore, treatment effects also were evaluated with year as a random effect in the model (table 1). When years were considered to produce random effects, the probability that differences in date of first estrus, date of lambing and percentage of ewes giving birth in the first 17 d of the lambing season was due to treatment was reduced to P<.5, P<.1 and P<.1, respectively. A treatment x year interaction was not observed (P>.5) for percentage of ewes lambing, number of lambs born per ewe exposed or number of lambs born per ewe lambing. No treatment effect on percentage of ewes lambing (P>.5) was observed, but a breed difference (P<.5) was evident. Suffolk ewes exposed to DC with sterile rams had a lower percent lambing (P<.1) than ewes exposed to FC with sterile rams, while ewes with NC with sterile rams had an intermediate lambing percentage. Over all treatments, crossbred ewes had a higher (P<.5) percentage of ewes lambing than did Suffolk ewes. Number of lambs born per ewe exposed was not different (P>.5) among treatments or years. However, a breed difference was evident, with crossbred ewes (1.96 +.7) having more lambs (P<.1) than purebred Suffolk ewes (1.36 +.1). The breed difference also was present when number of lambs born was expressed on a per-eweqambing basis (P<.1 ; 1.71 +.8 for Suffolk ewes, 2.15 +.5 for crossbred ewes). Regression coefficients, (within breed, year and treatment) of reproductive traits on body weight at the beginning of breeding are shown in table 2. Percentage of ewes ovulating before breeding was not influenced (P>.1) by body weight at breeding. For each 1 kg increase in body weight at the beginning of breeding, date of first observed estrus and date of lambing were delayed (P<.1) by.14 and.15 d, respectively. Percentage of ewes lambing in the first 17 d of the lambing season was decreased

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EXPOSURE OF EWES TO RAMS BEFORE BREEDING 1177 TABLE 2. REGRESSION COEFFICIENTS WITHIN YEAR, BREED AND TREATMENT FOR REPRODUCTIVE CHARACTERISTICS OF EWES ON WEIGHT AT THE BEGINNING OF BREEDING Trait Regression Standard error Percentage of ewes ovulating before breeding Date of first observed estrus Date of lambing Percentage of ewes lambing in the first 17 d Percentage of ewes lambing No. of lambs born/ewe exposed No. of lambs born/ewe lambing --.48.3.14"*.4.15"*.5 --.75*.31 --.38 t.21.12"*.6.22**.5 tp<.1. *P<.5. **P<.1. (P<.5) by.75 for each 1 kg increase in body weight. In addition, there was a tendency (P<.1) for a lower percentage (-.38/kg) of ewes to lamb as body weight increased. Lamond et al. (1973) obtained low reproductivity with both high- and low-energy diets, observing low fertilization rates when mature ewes were fed high-energy diets and low ovulation rates when fed low-energy diets. However, the number of lambs born per ewe exposed to the rams and the number of lambs born per ewe lambing were increased (P<.5) by.12 and.22 lambs/kg increase in body weight at the beginning of breeding. Exp. 2. No treatment, breed or treatment x year interaction effects were evident (P>.5) for percentage of ewe lambs ovulating before breeding (table 3). A year effect was observed (P<.5) for percentage of ewe lambs ovulating before breeding, with 74. + 5., 93.3 + 5.2 and 81.6 + 6.% of the lambs ovulating before breeding in yr 1, 2 and 3, respectively. Treatment, breed and treatment year interaction effects were not detected (P>.5) for date of first estrus, date of lambing or percentage lambing in the first 17 d of the lambing season. There was a tendency for ewe lambs with DC to lamb earlier (P<.1) than those with FC to sterile rams. Year differences were detected (P<.5) for date of first estrus, with ewe lambs observed in estrus earlier each succeeding year than the year before. A year difference was also detected (P<.5) for the percentage of ewes giving birth in the first 17 d of the lambing season. Dyrmundsson and Lees (1972) exposed Clun Forest ewe lambs to vasectomized TABLE 3. LEAST-SQUARES MEANS AND STANDARD ERRORS FOR REPRODUCTIVE CHARACTERISTICS OF EWE LAMBS Trait Treatment a No. of ewes DC FC NC Percentage ovulating before breeding 15 Date of first observed estrus b 149 Date of lambing b 124 Percentage lambing in first 17 d 124 Percentage lambing 15 No. born/ewe exposed 5 No. born/ewe lambing 124 9.5 + 4.8 8.7 4.8 77.7 4.9 298.8 +.8 298.8.8 3.1 +-.8 8.1 1.3 83.7 1.3 81.1 1.3 82.9 + 5.6 8.7 5.9 92.5 + 5.9 83.7 5.7 79. 5.7 8.1 -+ 5.9 1.24.11 1.16.11 1.17.1 1.49.8 1.48.9 1.47. adc=direct contact with sterile rams; FCffence contact with sterile rams; NC=no contact with sterile rams. No treatment year interactions were detected (P>.5) for any of the reproductive traits. b Julian calendar dates.

1178 HUDGENS ET AL. rams during the transition from non-breeding to breeding activity and found that rams did not affect mean date of onset of estrous activity, but did result in a high degree of synchronization at first mating. The percentage of ewe lambs giving birth was not different (P>.5) among treatments, years or breeds. Number of lambs born per ewe exposed was not different (P>.5) among treatments, years or breeds, nor was the number of lambs born per ewe lambing (table 3). There was a tendency (P<.IO) for the number of lambs born per ewe exposed to be greater for crossbred ewe lambs (1.31 +.8) than for Suffolk ewe lambs (1.7 -+.11). Regression coefficients for reproductive traits using body weight at the beginning of breeding as a covariate are shown for ewe lambs in table 4. Percentage of ewe iambs ovulating before breeding was increased (P<.1) by.155 for each 1 kg increase in body weight. Date of first observed estrus, date of lambing were not influenced (P>.1) by body weight. There was a tendency (P<.1) for percentage of ewe lambs giving birth to increase (.1 -+.57) as body weight increased. Number of lambs born per ewe exposed to the rams and the number of lambs born per ewe lambing were increased (P<.1) by.33 and.21 lambs/kg increase in body weight at the beginning of breeding. Age of the ewe lambs at the beginning of breeding did not (P>.5) influence any of the parameters measured (mean age = 251 + 1 d). This contradicts results reported by Burfening and Berardinelli (1986), who found that age was approximately four times more important than weight at the start of breeding in deter- mining percentage of ewe lambs that would exhibit estrus and lamb. Other researchers have reported that older ages and heavier body weights of ewe lambs at mating are associated with better lambing performance in terms of both ewes lambing and number born (Dyrmundsson, 1981). However, this relationship may not exist once the ewe lambs are above a certain threshold for body weight (Keane, 1974). A treatment effect was observed the first year when ewe lambs were lighter than in the second and third years. This suggests that lighter ewe lambs may respond to a ram effect during the natural breeding season, but if they have reached a threshold for body weight, a very high percentage will be having estrous cycles and no benefit from exposure to vasectomized rams will be realized. In summary, mature Suffolk and Suffolkcross ewes responded to the introduction of vasectomized rams during the transition from non-breeding to breeding activity by having a larger percentage of ewes ovulating prior to breeding, mating earlier in the breeding season and lambing earlier during the lambing season. Contact with rams did not influence percentage of ewes lambing but exerted a negative influence on litter size. Ram contact prior to breeding appeared to have no effect on date of mating, date of lambing or number of offspring born in these Suffolk and Suffolk-cross ewe Iambs. However, the ram contact occurred during the natural breeding season, while that in the ewes occurred during transition from anestrus to estrus. Heavier weights (and higher condition scores) were associated with delayed estrus in TABLE 4. REGRESSION COEFFICIENTS WITHIN YEAR, BREED AND TREATMENT FOR REPRODUCTIVE CHARACTERISTICS OF EWE LAMBS ON WEIGHT AT THE BEGINNING OF BREEDING Trait Regression Standard error Percentage of ewes ovulating before breeding Date of first observed estrus Date of lambing Percentage of ewes lambing in the first 17 d Percentage of ewes lambing No. of lambs born/ewe exposed No. of lambs born/ewe lambing.155"*.47 -.6.8.1.13 --.18.O56.1 t.57.33**.11.21"*.8 tp<.lo. **P<.O1.

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