Influence of body weight and number of inseminations on fertility of progestogen-treated ewe lambs raised in controlled environments

The influence of body weight at breeding on reproductive response to one and two artificial inseminations (AI) of fresh extended semen was assessed in 195 crossbred ewe lambs selected for early breeding and compared with 159 adult ewes, all housed indoors in a controlled environment. In six trials, ewe lambs and adult ewes in progestogen-induced estrus were inseminated 55 to 57 h after sponge removal. One-half of the lambs and one-fourth of the adults received a second insemination at 60 h. Resultant reproductive performance of both groups indicated no advantage in a double insemination. Overall fertility, litter size and fecundity after one and two inseminations were 33%, 1.7 and .6 for ewe lambs and 68%, 2.4 and 1.6 for adult ewes, respectively. Embryonic mortality after the first 2 wk of pregnancy was estimated at 24% for ewe lambs and 9% for adults. The influence of body weight was analyzed by grouping the ewe lambs according to body weight at breeding. The lambs in group 1 weighed 30 to 35 kg; group 2, 36 to 40 kg; group 3, 41 to 45 kg and group 4, 46 to 50 kg. The proportion of ewes lambing in groups 1, 2, 3 and 4 was 16, 34, 39 and 48%, respectively. Corresponding litter sizes were 1.4, 1.6, 1.8 and 2.0. Fecundity increased (P less than 01) from .2 in group 1 to 1.0 in group 4. The results indicate that even when ewe lambs are bred by AI (eliminating a ram behavioral problem), sheep with heavier body weights produce more lambs per ewe bred.     

Effect of megestrol acetate and progesterone on oestrous and fertility in cyclic Malpura and Chokla ewes

In Rajasthan, India megastrol acetate and progesterone were administered to ewes (25 Chokla, 25 Malpura, aged between 3 and 4) in November 1968. Each ewe received 50 mg of either megastrol acetate or progesterone. Administration was intravaginal or intramuscular. During treatment only 3 ewes (2 megastrol acetate-injected and 1 progesterone-injected ewes) came into heat; thus, the progestogens exerted an inhibiting effect. 76% and 88% of the megastrol acetate and progesterone ewes, respectively, exhibited heat within 96 hours of therapy's end. Breed showed no significant effect on occurrence of estrus after therapy. Release of estrus within 96 hours occurred in 91.3% and 74.0% of intravaginally and intramuscularly treated ewes, respectively. 17 (41.5%) of the 41 ewes inseminated at their synchronized estrus lambed as a result of breeding in that first cycle. Thus, questions arise as to efficiency of ovulation, fertilization, nidation, and lambing in the case of synchronized estrus by use of different progestogens. 75% of ewes showing typical fern pattern at insemination lambed. An antiseptic vaginal douche applied after withdrawal of the sponge used in iv administration might be responsible for increased posttreatment fertility in this group.     

Inhibitory Effect of Selenium Supplementation on the Reproductive Performance in Synchronized Merino Sheep at Range Conditions in a Selenium-deficient Area

The effect of selenium (Se) supplementation on the reproductive performance of Merino ewes mated out of the normal breeding season was studied in a 2 (no Se supplementation vs Se supplementation) × 2 (ewes mated at natural oestrus vs synchronized oestrus) factorial design with 50 ewes per treatment combination. Synchronization of oestrus was achieved by intravaginal insertion of 40 mg cronolone sponges for 14 days and administration of 440 IU PMSG at sponge withdrawal. Se supplementation was by the addition to the concentrate with 0.5 mg/kg of Se in the form of selenomethionin, for the 3 months prior to the mating and during gestation. Ewes were kept under range conditions in south‐west Spain, and exposed to Merino rams at a female: male ratio of 4 : 1 from 2 days following sponge withdrawal, or the equivalent time, for 21 days. Se supplementation alone did not improve significantly ewe fertility or lamb birth weight, but there was a positive effect of synchronizing ewes mated out of the breeding season as more of these ewes lambed and produced more lambs than those not synchronized. However, a strong interaction was found between synchronization and Se supplementation, causing a deleterious effect on the reproductive performance of ewes. This negative effect, presumably related to high embrionary mortality caused by Se toxicity, should be taken into account for oestrus synchronizing in Se‐deficient areas. The supplementation with Se, for the prevention of nutritional myodystrophy degeneration in lambs, should be conducted in a fashion which does not generate high levels of Se in the ewes around the mating period.     

Estrus Synchronization in Sheep and Goats Using Combinations of GnRH,Progestagen and Prostaglandin F2α

The objective of this experiment was to evaluate the effect of GnRH, progestagen and prostaglandin F_2α on estrus synchronization in sheep and goats. Sixty Awassi ewes and 53 Damascus does were used in the study. The experiment started at the beginning of the breeding season (June/July). The same treatments were applied to sheep and goats as follows: no treatment (CON), 14‐day progestagen sponges and 600 IU equine chorionic gonadotropin (S), gonadotropin releasing hormone followed 5 days later by prostaglandin F_2α (GP) and gonadotropin releasing hormone, progestagen sponges for 5 days and prostaglandin F_2α on the day of sponge removal (GSP). None of the ewes in the S group lambed from mating during the induced cycle. A greater lambing rate (p < 0.05) was observed in the GSP group compared with the CON and S groups while the GP group was intermediate. The number of lambs born per lambed ewe was similar among the CON, GP and GSP groups. However, the number of lambs per exposed ewe was greater (p < 0.05) in the GSP than the remaining groups. The induced cycle kidding rate was 77% for all treatments combined. Similar kidding rate were observed among treatments. The numbers of kids born per kidded and exposed doe from mating during the induced estrus were also similar among treatments. Greater numbers of multiple births were observed in the GP and GSP than in the S group. In conclusion, a combination of GnRH, progestagen sponges and PGF_2α can be effective in synchronizing estrus and improving fecundity in sheep and goats. Although the use of GnRH–PGF_2α was effective, the addition of progestagen sponges at the time of GnRH administration appeared to improve reproductive parameters.     

Fertility of ewes given either melatonin or progestogen sponges

The administration of melatonin via intravaginal sponges is an effective method of advancing the breeding season in ewes. In the present study the fertility of melatonin-treated ewes has been compared with that of ewes induced to ovulate by conventional treatment. On June 25, 15, 15-month-old ewes (group 1) were given intravaginal implants containing melatonin in silastic tubing. On August 8, 13 similar ewes (group 2) were given Veramix sponges which were removed 12 days later, when they were given 500 iu pregnant mare's serum gonadotrophin (PMSG). Two intact raddled rams were introduced to the combined groups on August 21. The mean date of mating was September 3 +/- 1.5 for group 1 and August 21 +/- 0.2 for group 2 ewes. All the ewes in group 1 and 10 in group 2 (77 per cent) were mated. All the ewes were slaughtered approximately 50 days after mating and their reproductive tracts removed. The mean ovulation rates were 2.1 and 2.3 in groups 1 and 2, respectively. The results indicate that conception rates of 87 per cent and 61.5 per cent of ewes put to the ram were obtained in the melatonin-treated and PMSG-treated groups, respectively. At slaughter the melatonin-treated group were found to have a mean of 1.47 live fetuses per ewe put to the ram and the PMSG-treated group a mean of 1.08. It can therefore be concluded that melatonin implantation is an effective method for the advancement of seasonal breeding in anoestrous sheep, and that the fertility achieved is at least as good as that given by conventional progestogen-PMSG treatment.     

Effect of feed treatment and exogenous estrogen and progestogen on puberty and lambing rates in ewe lambs

Four hundred seventy-four ewe lambs (5 to 6 mo of age) were assigned within breed to two postweaning feed treatments; 1 = alfalfa pellets ad libitum and 2 = alfalfa pellets plus 20% barley or wheat ad libitum. Ten days prior to the start of breeding, approximately one-half of the ewe lambs within each feed treatment were treated with a single injection of 2.5 mg of estradiol valerate and 1.5 mg of norgestomet and implanted with 3 mg of norgestomet for 8 d. At the start of breeding, fertile Suffolk rams were fitted with marking harnesses and penned with ewe lambs; evidence of estrus and breeding was determined on a weekly basis by visual examination for breeding marks. In the second year of the study, 7 to 13 d after recording estrous activity, all marked ewe lambs were bled; and blood was assayed for progesterone. In 1983, 60% of the ewe lambs showed estrus and 11% lambed compared with 48% exhibiting estrus and 30% lambing in 1984 (P less than .01). More (P less than .01) ewe lambs on feed treatment 1 displayed estrus, but more (P less than .05) lambed in the feed treatment 2 group. Steroid treatment resulted in more (P less than .01) ewe lambs showing estrus but fewer lambing (P less than .01). Examination of progesterone concentrations for evidence of ovulation and corpus luteum development indicated that treatment with steroids caused a large percentage of ewe lambs to exhibit estrus. However, many of these failed to develop a corpus luteum and become pregnant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of concentration, duration and route of administration of melatonin on reproductive performance of spring-mated polypay and polypay-cross ewes

The effects of exogenous melatonin on reproductive performance of 737 Polypay and Polypay-cross ewes were evaluated during a late March and April breeding period. Different concentrations (2 or 10 mg) routes of administration (fed vs implanted) and durations of administration (20 or 40 d before breeding) were studied. Estrus was synchronized in all ewes using 60 mg medroxyprogesterone acetate (MAP) in a vaginal pessary. Number of mature ewes lambing/ewe present at lambing was increased (P less than .05) nearly 20% by implanting for 40 d with melatonin (75%) or by feeding either 2 (72%) or 10 mg (73%) melatonin for 40 d before spring breeding compared with untreated control ewes (54%) or ewes implanted for only 20 d before breeding (58%). Date of lambing, number of lambs born/ewes lambing and number of lambs born alive/ewe lambing were not altered significantly by treatments. Number of yearling ewes (n = 166 for ewes 1.5 yr old at lambing time) lambing/ewe present at lambing was lower (P less than .01; 26%) than that of mature ewes (n = 381, greater than or equal to 2.0 yr; 68%). We concluded that feeding 2 or 10 mg melatonin or implanting melatonin for 40 d enhanced reproductive performance and effectively overcame the restrictions of seasonality of breeding in mature ewes. In yearling ewes, 10 mg melatonin increased the number of ewes lambing.     

Reproductive performance of Suffolk and Suffolk-cross ewes and ewe lambs exposed to vasectomized rams before breeding

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 400 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 Suffolk-cross ewes was utilized during the 3-yr experiment. A greater (P less than .05) 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 greater than .05) 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.     

Effect of feed flushing during summer season on growth, reproductive performance and blood metabolites in Malpura ewes under semiarid tropical environment

Feed scarcity during hot summer months is one of the major predisposing factors for low reproductive efficiency of livestock reared in hot semiarid environment. A study was conducted to assess the effect of concentrate supplementation during summer months on growth, reproductive performance, and blood metabolites in Malpura ewes. Twenty adult Malpura ewes were used in the present study. The ewes were divided into two groups viz, group 1 (n?=?10; control) and group 2 (n?=?10; concentrate supplementation). The study was conducted for a period of 35 days covering two estrus cycles. In the first cycle, only PGF_2α was given to all ewes, while in second cycle, all ewes were synchronized for estrus using progesterone-impregnated intravaginal sponges and pregnant mare serum gonadotropin. The animals were allowed for grazing for 8–10 h per day. Apart from grazing, group 2 ewes were supplemented with concentrate mixture at 1.5 % of body weight. Concentrate supplementation had significant influence on body weight, ADG, estrus percentage, estrus duration, onset of estrus, ovulation response, plasma glucose, total protein, and urea. The present study reveals that ewes supplemented with concentrate mixture at 1.5 % of body weights during summer season significantly influenced the growth and reproductive performance of Malpura ewes. Further, the study signifies the importance of providing additional feed supplementation to ewes kept grazing under the conditions of a hot, semiarid environment to improve their reproductive efficiency.     

Effect of prenatal testosterone treatment on nitrogen utilization and endocrine status of ewe lambs

Thirty-eight pregnant Suffolk ewes were assigned randomly to a control group or implanted with approximately 2 g of testosterone propionate (TP) when they were between d 40 and 60 of gestation. Implants were removed 3 wk prior to lambing. Five ewe lambs born to implanted ewes and ten ewe lambs born to nonimplanted ewes were utilized in this experiment. Ram lambs were not used in this trial. No differences (P greater than .10) were observed for fecal, urinary and total N excretion and amount of N absorbed. Nitrogen retained (percentage of N intake and g/d) was higher (P less than .05) in prenatally androgenized ewe lambs than in control ewe lambs. Plasma insulin concentrations averaged 99% higher (P less than .05) in prenatally androgenized ewe lambs. Plasma insulin-like growth factor I (IGF-I) concentrations averaged 29% higher (P less than .06) in ewe lambs treated prenatally with testosterone. Nonesterified fatty acid (NEFA) concentrations averaged 41% higher (P less than .05) in prenatally androgenized ewe lambs. Significant (P less than .05) treatment x time effects were observed in plasma thyroxine, glucose and urea N concentrations of prenatally androgenized vs control ewe lambs. These significant modifications in the plasma metabolite and endocrine status could be an important element of the physiological mechanism(s) by which prenatal androgenization improves growth performance and leanness of ewe lambs.     

Effects of sarcoptic mange on the reproductive performance of ewes and transmission of Sarcoptes scabiei to newborn lambs

In each of two experiments, the reproductive performance of ewes naturally infested with sarcoptic mange and of uninfested ewes was assessed in in-season natural breeding conditions (experiment I) or in out-of-season controlled breeding conditions (experiment II). A statistically significant difference was observed in the total lambs born per ewe (infested ewes, 1.2; controls, 1.6), in the liveborn lambs per ewe (infested ewes, 1.2; controls, 1.5) and in the lamb body weight per ewe (infested ewes, 3.33kg; controls, 4.53kg) under natural breeding conditions, as well as in the lamb body weight per ewe (infested ewes, 3.37kg; controls, 4.14kg) among ewes under controlled breeding conditions. No adverse effects were observed in the other reproductive indices, cycling rate, mating rate, return-to-oestrus rate, abortion rate, lambing rate and stillbirth rate. Sarcoptic mange was observed in the offspring of infested ewes after 30 days and in the offspring of uninfested controls 60 days after their birth.     

Estrus synchronization in sheep with synthetic progestagens

Sixteen female sheep of Degua breed were assigned to receive either the full dose of norgestomet ear implant and injectable solution containing norgestomet and estradiol valerate (n = 8) or half the dose (n = 8). The ear implants were removed in both groups on day 12. All ewes received an intramuscular administration of 500 IU PMSG at implant withdrawal. Synchronized ewes were individually hand mated twice at 48 and 60 hours after implant removal. One ewe in each group however refused mating on both occasions. Pregnancy diagnosis was conducted by bimanual external palpation 90 to 100 days post mating. The conception rates (3/7, 42.85%) and (5/7, 71.42%) were recorded in the two treatment groups, respectively. All eight ewes lambed between 145 to 153 days post mating. In group I ewes carried only singletons (prolificity rate 1.0) whereas in group II two ewes delivered twins, producing 7 lambs with prolificity rate of 1.4 (N.S). From this preliminary investigation it appears that the lower dose of norgestomet ear implants offers better option for estrus synchronization accompanied by higher fertility.     

Influence of PMSG and time of artificial insemination on fertility of progestogen-treated sheep in confinement

The need for pregnant mates' serum gonadotropin (PMSG) in breeding confined sheep by artificial insemination (AI) at progestogen-synchronized estrus was assessed in 152 adult crossbred ewes brought into season by a controlled light regimen. One-half of the ewes received 500 IU PMSG after intravaginal progestogen treatment; all ewes were inseminated either 54, 57 or 60 h after sponge removal or at 54 and again at 60 h. Based on progesterone determinations 18 d after AI, conception rates with single insemination 54, 57, or 60 h and double insemination at 54 and 60 h were 76, 72, 47 and 72%, respectively, among ewes receiving PMSG, compared to 17, 22, 47 and 43%, respectively, among ewes not give PMSG (P less than .01) Lambing rates were higher (P less than .01) with PMSG (67, 67, 37 and 61%) than without PMSG (11, 11, 26 and 33%). While there was only a small increase (.06 less than P less than .05) in litter size with PMSG, fecundity decreased (P less than .01) from 1.4 to .3 when PMSG was not used. These data indicate that, even with controlled lighting to induce estrous activity, additional stimulation of ovulation by PMSG at progestogen-synchronized estrus is necessary for normal fertility when confined sheep are bred by AI.     

羊同期发情腹腔镜输精最佳时间的研究

[目的]确定羊同期发情腹腔镜输精的最佳时间。[方法]选取繁殖机能正常、营养状况良好的适龄母羊,在试验母羊阴道内放置孕酮海绵栓10~14 d,撤栓时肌肉注射250~330 IU/只孕马血清促性腺激素（PMSG）。撤栓后12~24 h开始试情,早晚各1次。按撤栓后时间及发情时间不同分4组进行腹腔镜输精：1组为撤栓后46~50 h输精（n=138）,2组为撤栓后50~54 h输精（n=156）,3组为撤栓后54~58 h输精（n=275）,4组为羊发情后30~36 h输精（n=226）。输精后第40~45天进行B超检查,计算各组母羊受胎率。[结果]发情后30~36 h输精的母羊（4组）受胎率最高,为97.79%,其次为撤栓后50~54 h输精的母羊（2组）,受胎率为97.44%,撤栓后46~50 h输精的母羊（1组）受胎率为91.30%;撤栓后54~58 h输精的母羊（3组）受胎率最低,为89.82%。[结论]采用同期发情配合腹腔镜输精技术进行母羊人工授精,最佳输精时间为撤栓后50~54 h以及母羊发情后30~36 h。     

The effect of castration, estradiol and LHRH on LH secretion of lambs fed different levels of dietary energy

To examine the effect of diet on luteinizing hormone (LH) secretion, basal and luteinizing hormone releasing hormone (LHRH)-induced LH release was compared in intact or castrated-estradiol-17 beta implanted Finn-Dorset lambs. Ten to 12 wk old ram (n = 20) and ewe lambs (n = 20) were maintained under a 8L:16D photoperiod and fed for high (HG, 163 to 168 g/d) or low (LG, 76 to 103 g/d) rates of gain. Eight to 10 wk later, baseline LH concentrations were determined in blood samples collected at 20 min intervals for 7 h. The following day, lambs were given an iv injection of 5 micrograms of estradiol-17 beta followed within 4 h by LHRH (.5 or 2.5 micrograms). Baseline concentrations of LH for HG ewes were threefold greater than for LG ewes (4.2 vs 1.4 ng/ml), respectively. Time to peak response was inversely related to dietary energy level (P less than .025). Basal LH levels were similar across diets in rams. Total LH release following LHRH was dose-dependent (P less than .005). Effects of gonadal feedback were tested in a second group (n = 24) of castrated lambs. Changes in LH secretion were not different between diets within 3 to 4 wk after castration. A subcutaneous silastic implant (22 mm) of estradiol-17 beta inhibited (P less than .01) LH concentrations across diets in both ewes and rams. No differences in estradiol feedback on LH secretion (at the dose of steroid tested) were detected between HG and LG lambs. Within 8 d, however, basal LH concentrations were 60% lower (P less than .01) in HG vs LG ewes. Furthermore, peak LHRH-induced LH release was greater (P less than .025) in LG vs HG lambs of both sexes. Estradiol inhibited basal LH secretion in ewes and rams but facilitated LH release in lambs with a reduced rate of gain.     

Evaluation of melengestrol acetate and equine chorionic gonadotropin for out-of-season breeding in sheep on Prince Edward Island

The purpose of this study was to compare the efficacy of a recommended protocol of oral melengestrol acetate (MGA) to intravaginal medroxyprogesterone acetate (MPA), with or without equine chorionic gonadotropin (eCG), for out-of-season breeding of sheep on Prince Edward Island. One hundred and twenty ewes were assigned to 1 of 4 groups in a factorial design and were treated with either an intravaginal MPA sponge or oral MGA. Ewes received either an intramuscular injection of eCG or a saline placebo at cessation of progestogen treatment. The reproductive performance was best for the MPA-eCG group, followed by the MGA-eCG, MGA-saline, and MPA-saline. Pregnancy rates of 66.7%, 43.3%, 31.0%, and 16.7%, respectively, and ratios of lambs born to ewes exposed to the ram of 1.17, 0.63, 0.52, and 0.23, respectively, were recorded for these groups. We concluded that, under the conditions of this study, the use of oral MGA resulted in fewer lambs than did the use of MPA sponges with eCG. Nonetheless, the use of MGA may be attractive to producers because it is less expensive and more convenient than the use of sponges.     

Evaluation of the ovine callipyge locus: IV. Genotypic effects on reproductive traits

A resource population of ewes derived from Dorset and Romanov grandparents was generated over 5 yr to provide genotypic and phenotypic data to estimate effects of each callipyge genotype on component traits of reproduction. Effects on ovulation rate were estimated from data recorded by examination of ovaries from serially slaughtered ewe lambs (n = 174) born in 1994 and 1995. Productivity and longevity through 5 yr of age were recorded on a total of 265 F2 ewes produced in 1996 through 1998. Number of lambs born, birth weights, and weaning weights of lambs were calculated for each ewe. Weaning weight was recorded for each lamb and adjusted for age to 56 and 32 d for dam- and nursery-reared lambs, respectively. Longevity was determined as a binary trait based on the presence or absence of the ewe in the breeding flock at 5 yr of age. Ewes generated 937 records for breeding weight and 925 records for conception rate, which was determined on ewes exposed and still present at the start of each lambing season. Seven hundred seventeen records were analyzed for traits based on the number of ewes lambing. Genotypes for the causative callipyge mutation were determined using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. Each ewe was classified into 1 of 4 genotypes; NMatNPat, NMatCPat, CMatNPat, or CMatCPat, where N represents wild type and C represents the mutant allele. The mean ovulation rate of the ewe lambs genotyped NMatNPat was greater (P < 0.02) than that exhibited by NMatCPat; however, the estimated difference of 0.25 ovum in the ewe lambs did not affect the number born. The live weight of NMatCPat ewes at breeding was 2.5 kg less than that of other genotypes (P < 0.01). The callipyge genotype class did not significantly affect conception rates, fecundity, maternal ability, or ewe longevity. Maintaining a ewe flock to produce homozygous mutant rams for use in terminal sire mating systems presents no unusual problems from a reproduction standpoint.     

Effect of prolonged exposure to exogenous melatonin on the onset and end of the breeding season and on the growth rate of ewe lambs

The effect of prolonged exposure to exogenous melatonin on the reproductive status and growth rate of ewe lambs was investigated. Ewe lambs (born late March) were given intravaginal melatonin implants on 4 July (group J, n = 10) during anoestrus, or 20 December (group D, n = 10) during the breeding season. A third group (group C, n = 7) received empty implants on 4 July. Plasma progesterone concentrations were used to assess reproductive status. In the control group cyclic ovarian activity began on November 15 +/- 4 days, and ceased on January 28 +/- 8 days. In group J the onset of the breeding season was advanced by 4.9 weeks (occurring on October 12 +/- 4 days; P less than 0.001). The onset of anoestrus was also advanced in this group with 9 out of 10 of the ewes ceasing ovarian activity at least 3.4 weeks in advance of the control ewes (P less than 0.01). In contrast the timing of anoestrus was unchanged in group D, occurring on February 14 +/- 6 days. Melatonin treatment of ewe lambs from early July had no effect on growth rate, whereas treatment from mid-December had a depressive effect. Ewes therefore become refractory to the inductive effects of exogenous melatonin after long-term exposure. The results are consistent with the view that photorefractoriness is due to changes in the processing rather than the generation of the melatonin signal.     

Reproductive performance of totally confined sheep bred with semen extended in a lactose-egg yolk-glycerol buffer and stored at 5 degrees C.

Two experiments were carried out in January and May 1975 to study reproductive performance (fertility, prolificacy and fecundity) of totally confined sheep synchronized for estrus. The main objective of the first experiment was to compare reproductive performance of ewes bred naturally to those bred by artificial insemination. Semen for artificial insemination was collected by either artificial vagina or electroejaculation and stored for up to 36 hours at 5 degrees C. A second objective was to evaluate the effect of pregnant mares' serum gonadotrophin on the reproductive performance of ewes synchronized for estrus. Fertility was 53% for ewes bred by natural mating, 34% for ewes receiving pregnant mares' serum gonadotrophin and bred by artificial insemination, and 9% for those not receiving pregnant mares' serum gonadotrophin and bred by artificial insemination. There was no difference in fertility between ewes bred with semen collected by artificial vagina or by electroejaculation. A similar pattern was observed for fecundity. Average prolificacy was 2.0 with no significant differences among mating methods or pregnant mares' serum gonadotrophin application being observed. In the second experiment, the reproductive performance of ewes inseminated with semen stores at 5 degrees C for 48 to 60 hours was compared to that of ewes inseminated with semen stores for 24 to 36 hours. No significant differences in the reproductive performance were detected. Although average fertility (9%) and fecundity (19%) were low, prolificacy averaged 2.0 lambs per ewe lambing.     

Influence of body weight, age, and weight gain on fertility and prolificacy in four breeds of ewe lambs

Breeding ewes to lamb at 1 yr of age can improve profitability for some production systems. The first objective of this study was to evaluate the effect of age and weight at breeding and total postweaning weight gain on reproductive performance of ewe lambs. The second objective was to compare the effects of weight and age variables in four major sheep breeds (Columbia, Polypay, Rambouillet, and Targhee). Weights, ages, and the binary traits of fertility (pregnant or nonpregnant) and prolificacy (one lamb born vs. two or more) were collected on 2,055 ewe lambs at the U.S. Sheep Experiment Station, Dubois, ID, from 1984 through 1988. The effects of age and weight at breeding and total weight gain from weaning to breeding on fertility and prolificacy were analyzed with a logit model in a maximum likelihood analyses. Differences (P < 0.001) among breeds for fertility were identified, with a 93% fertility rate for Polypay ewe lambs compared with lower fertility rates in Columbia, Targhee, and Rambouillet ewe lambs (50, 60, and 75%, respectively). The percentage of multiple births (prolificacy rate) also was higher (P < 0.001) in the Polypay (47%) than in Columbia, Targhee, and Rambouillet breeds (1, 13, and 14%, respectively). Averaged across breeds, weight at breeding had a positive effect on fertility and prolificacy (P < 0.001), whereas total weight gain from weaning to breeding had a positive effect only on fertility (P < 0.027). In separate analyses for each breed, increasing age (P < 0.001) and weight at breeding (P < 0.001) increased the probability of pregnancy in Rambouillet ewe lambs. The probability of pregnancy for Targhee ewe lambs increased (P < 0.005) with weight at breeding. Increasing weight at breeding increased (P < 0.004) the probability of multiple births in all breeds. Increasing total postweaning weight gain increased (P < 0.007) the probabilities of multiple births in Rambouillet and Targhee ewe lambs. In conclusion, Polypay ewe lambs were superior in fertility and prolificacy to Columbia, Rambouillet, and Targhee under Western range conditions. Improved reproductive performance of Columbia, Rambouillet, and Targhee ewe lambs may be achieved by increasing age and weight at breeding and postweaning gain.