Use of progestagen-gonadotrophin treatments in estrus synchronization of sheep

The main objective of this study was to investigate the effectiveness of certain progestagen-gonadotrophin treatments on synchronization of estrus in sheep. In Experiment I, 30 Chios ewes were treated at the beginning of the breeding season with medroxyprogesterone acetate (MAP) intravaginal sponges for 12 days and a single i.m. treatment of either FSH (Group 1,10 IU, n = 8; Group 2, 5 IU, n = 8; Group 3, 2.5 IU, n = 8) or eCG (Group 4, 400 IU, n = 6) at the time of sponge removal. Ten days after sponge removal laparotomy was performed to record ovarian response. Clinical estrus was observed in more (though not at a significant level) FSH treated than eCG treated sheep (62.5% versus 33.3%). Administration of 400 IU eCG resulted in the highest mean number of CL perewe ovulating (2.8 +/- 0.2), with administration of 10 IU FSH producing the next best results (2.1 +/- 0.3). Statistically significant differences in the mean number of CL per ewe ovulating were found only between ewes in Group 3 (1.7 +/- 0.4) and Group 4 (2.8 +/- 0.2) (P < 0.05). In Experiment II, 53 Chios and 30 Berrichon ewes were treated during the mid-breeding season with MAP intravaginal sponges for 12 days and a single i.m. treatment of either 10 IU FSH (27 Chios and 16 Berrichon ewes) or 400 IU eCG (26 Chios and 14 Berrichon ewes), at the time of sponge removal. Ewes that were in estrus on Days 2-4 and 19-23 after sponge removal were mated to fertile rams. No significant differences were recorded between treatment or breed groups in the proportions of ewes observed in estrus after treatment. In the Berrichon breed, FSH administration resulted in higher lambing rates (93.8% versus 57.1%, P < 0.05) and higher mean number of lambs born per ewe exposed to rams (1.4 +/- 0.2 versus 0.8 +/- 0.2, P < 0.05) than that of eCG. After treatment with eCG, the mean number of lambs born per ewe exposed to rams was higher in the Chios than the Berrichon breed (1.4 +/- 0.2 versus 0.8 +/- 0.2, P < 0.05). After treatment with FSH, the lambing rate was higher in the Berrichon than the Chios breed (93.8% versus 63.0%, P < 0.05). In conclusion, a single FSH treatment (5 or 10 IU) at the end of progestagen treatment appears to be more effective than eCG for the induction of synchronized estrus in sheep at the beginning of the breeding season, with no cases of abnormal ovarian response observed. During the mid-breeding season FSH (10 IU) appears to be equally as effective as eCG (400 IU) in respect of lambing rate and mean number of lambs born per ewe.     

Estimates of early embryonic loss in ewes mated to rams selected for high and low prolificacy

Two closed lines of sheep selected for high and low prolificacy were established in 1969. Rams within each line were selected on the basis of their dams' lambing records. Foundation ewes were assigned at random to selected rams, and no ewe selection was practiced until replacement yearlings were selected for mating. Selection of the rams used to mate the foundation ewes resulted in more lambs born per 100 ewes exposed to the ram (P<.10) and more lambs born per 100 ewes lambing from the high line rams (P<.05).Seven rams from each line were then used to estimate fertilization rate and embryonic survival rate when mated to an unrelated group of ewes. There was no difference in ovulation rate or fertilization rate of ewes mated to low and high line rams. Percent eggs recovered per CL was 80 and 92 (P<.01) for low and high line rams, respectively. At 35 days 82 and 86% of the ewes were pregnant, and 84 and 93% of the CL were represented by embryos in the pregnant ewes mated to low and high lines, respectively. Estimated embryonic survival rates were 81 and 89% in ewes mated to low and high line rams, respectively.     

A comparison between intravaginal progestagen and melatonin implant treatments on the reproductive efficiency of ewes

A total of 548 Manchega ewes were used to compare progestagen impregnated intravaginal sponges (12 days) plus eCG with melatonin implant (100 days) treatments, as possible stimulants of reproductive performance during the seasonal anoestrus and the lactation period. The use of both methods of oestrous manipulation induced a significant improvement in conception rate (78% for progestagen and eCG; 78% for melatonin versus 65% for the control) and fecundity (1.50 for progestagen and eCG; 1.55 for melatonin versus 1.26 for the control), when compared to the control group. Likewise, the lambing rate was also increased (1.17 for progestagen and eCG; 1.21 for melatonin versus 0.82 for control). A total of 35 and 39 extra lambs/100 ewes mated were produced, with an increase in productivity (percentage of extra lambs) of 43% and 48%, for ewes treated with progestagen sponges and melatonin, respectively, compared to the control group. The interval between ram introduction and parturition was significantly decreased, with matings in February–April (early seasonal anoestrus), compared to matings in March–May (seasonal anoestrus) in the group treated with progestagen sponges. An increase in the interval between parturition and the following mating was also recorded. As the body condition improved, the number of lambing ewes and fecundity were significantly improved in all groups. All the fertility results obtained with the progestagen sponges and melatonin treatments were similar. It could be concluded that progestagen sponges plus eCG and melatonin implants improved the reproductive performance of ewes, in seasonal anoestrus and during the lactation period, to a similar extent.     

Effects of retention of fetal membranes on subsequent reproductive performance of dairy ewes

Seventy-one pairs of ewes with or without retention of fetal membranes in the previous lambing season, were included in a cohort study of 25 flocks in southern Greece; in 27 pairs regulation of the breeding cycle was applied, whilst in the other 44 pairs natural mating took place. The following measures of reproductive performance were calculated: cycling rate, mating rate, return-to-estrus rate, abortion rate, lambing rate, total lambs born per ewe, liveborn lambs per ewe, stillbirth rate, lamb-bodyweight per ewe; furthermore, the incidence risk of retention of fetal membranes during the lambing examined in this study was also calculated. No statistically significant differences were observed in the reproductive performance among ewes that had or had not retained their fetal membranes during the previous lambing, whether the breeding cycle was regulated or not. The incidence risk of retention of fetal membranes among ewes that had not retained its placenta in the previous lambing was 1.6%, whilst that among ewes that had retained its placenta in the previous lactation was 0%. It is concluded that retention of fetal membranes did not appear to adversely affect subsequent reproductive performance of ewes.     

The relationship of libido and serving capacity test scores in rams on conception rates and lambing percentage in the ewe

A procedure for assessing sexual activity (libido) and serving capacity (number of ejaculations) in individual rams is described. Libido and serving capacity was measured by this procedure in 10 Lincoln, 10 Suffolk, 2 Columbia, and 2 Polypay rams prior to the breeding season. Semen was evaluated, and the scrotal circumference measured. The rams were single-sire mated to 10-12 whiteface, crossbred ewes during a 35-day breeding season (September 26 - October 29). First-service conception rates, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were calculated for each ram. The mean libido score for the 24 rams was 8.95 and the mean serving capacity score was 3.16. The 24 rams were classified as low serving capacity (<2 ejaculation), medium serving capacity (2-3 ejaculations), or high serving capacity (>3 ejaculations). There were no significant differences in either conception rate or lambing percentages between the 3 groups of rams. The first-service conception rate, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were 74.8, 93.8, 148.6, and 139.4 percent, respectively, for the 24 rams. Libido and serving capacity tests in the rams, as used in this experiment, prior to the breeding season, were not successful in predicting fertility or prolificacy in ewes.     

Fertility in South Australian commercial Merino flocks: sources of reproductive wastage

To identify reasons for low fertility in the Merino in South Australia, we defined the extent and sources of reproductive wastage in flocks of maiden (n=14) and mature age (n=54) Merino ewes managed on 43 properties over 4 year. In a second study, reproductive wastage was examined in a very high ovulating flock of mature age South Australian Merino ewes heterozygous for the FecB gene, mated to lamb in either the autumn or spring. Losses in the latter flock were examined in less detail than the large-scale study, but allowed wastage to be partitioned between pre- and peri/post-natal sources. In the first experiment, reproductive wastage between mating and weaning was estimated at 59.7 potential lambs or ova lost per 100 ewes exposed to rams, representing 42.4% of ova shed. The main source of wastage occurred at lambing (55.6% of total loss), with death of twins a major contributor (35.3% of total loss). Other important sources of wastage were from partial failure of multiple ovulation (PFMO; 20.4% of total loss) and from ewes mating but not lambing (13.2% of total loss). Reproductive wastage did not vary with either age of ewe (maiden versus mature) or season of mating (October-December versus January-March). Mean ovulation rate, estimated as 141 per 100 ewes ovulating (range 100-200), varied with age of ewe (129 versus 144; maiden versus mature) but not with season of mating or year (1990-1991). Values for fertility, fecundity and lamb survival were 90, 127 and 73%, respectively. Fecundity of maiden ewes was lower than that of mature ewes (116 versus 130). Survival of single and twin lambs between birth and tail docking was 83 and 56%, respectively. Net reproductive efficiency, or lambs weaned per 100 ewes exposed to rams, averaged 81 (range 31-122). In the second experiment, mean ovulation rate of FecB Merino ewes was 316 per 100 ewes ovulating, with 242 ova (potential lambs) lost between ovulation and tail docking. This loss was equally shared between pre- and peri/post-natal sources (123 versus 119), and demonstrates severe limitation of the Merino to successfully bear and rear multiple litters. We concluded that future research in commercial Merino flocks be focused on lamb mortality, particularly of twins, and on PFMO, the major source of embryo loss.     

Increasing ovulation rate and lambing rate in sheep by treatment with a steroid enzyme inhibitor

Treatment of ewes with a 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) inhibitor (Epostane) resulted in a significant increase in both ovulation rate and in the mean number of lambs per ewe lambing. The progestagen sponge plus 3 beta-HSD inhibitor treatment also caused a significant increase in oestrous cycle duration of approximately 1.5 days. Treatment of ewes with the 3 beta-HSD inhibitor caused a significant decrease in peripheral progesterone concentrations, which were reduced even further when 3 beta-HSD inhibitor treatment was given to ewes after insertion of a progestagen sponge. However, mean oestradiol concentrations were significantly higher in the two treatment groups, both at the end of the luteal phase and during the follicular phase of the oestrous cycle. These results demonstrate that ovulation rate and the production of lambs per ewe lambing can be significantly increased by 3 beta-HSD inhibitor treatment.     

Effects of long-term consumption of sewage solids on reproductive performance and serum progesterone and estradiol-17beta in mature fine-wool ewes

Eighty-four mature fine-wool ewes were randomly allotted to one of three dietary treatments to examine the influence of dietary sewage solids on reproductive performance. Treatments were a basal diet or basal plus either 3.5% cottonseed meal (CSM) or 7% sewage solids. Serum progesterone and estradiol-17beta measured in blood samples collected through an estrous cycle just before the breeding season of the first and second years were not adversely influenced by sewage feeding. Progesterone concentrations quantified in weekly blood samples collected during gestation and lactation of both years did not differ (P>0.10) among treatments. During the first lambing season, lambing data showed that ewes consuming CSM produced slightly more lambs per ewe exposed (P<0.10) than either basal- or sewage-fed ewes. During the second breeding season, midventral laparotomies revealed that ovaries from ewes receiving CSM contained more (P<0.10) corpora lutea than did those from either basal- or sewage-fed animals. However, at the end of the second lambing season, no differences (P>0.10) among treatments in the number of lambs born or weaned were observed. A third year's lambing data also revealed no difference (P>0.10) among treatments for lambing rates. These data indicate that prolonged consumption of a diet containing 7% sewage solids has little, if any, detrimental effect on reproductive performance of mature fine-wool ewes.     

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n = 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P < 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P < 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P < 0.05), while ewes mated to Lleyn sire breed had more dystocia (P < 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P < 0.001), and some to litter size (P < 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P < 0.05). Lamb live weight at weaning was higher with Texel- and Cheviot- and Lleyn-sired lambs compared with Blackface- and Swaledale-sired lambs (P < 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P < 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.     

Lambing rates and litter size following carazolol administration prior to insemination in Kivircik ewes

The effect of carazolol on the ease of penetrating the cervix during artificial insemination, lambing rate and litter size was studied using 1.5–4.0-year old Kivircik ewes in an incomplete 3 × 2 × 2 experimental design. All of the ewes in this study were synchronized for oestrus by insertion of a progesterone impregnated vaginal sponge for 12 days and administration of 400 IU PMSG at sponge withdrawal. Three methods of service were compared: natural service, artificial insemination (AI) with fresh semen, or AI with frozen semen. Two times of insemination (fixed time AI versus AI at observed oestrus) were compared on the fresh and frozen AI treatments. The absence (control) or use of carazolol (carazolol; 0.5 mg/ewe i.m. 30 min before mating) was the third factor in the design and penetration of the cervix by the insemination pipette was assessed as shallow (<10 mm), middle (10–20 mm) or deep (>20 mm). Natural service ewes were only mated at observed oestrus. Consequently, the factorial design was incomplete and there were a total of 10 treatments each represented by 30 ewes. Natural service resulted in a significantly (P < 0.05) higher lambing rate and litter size (86%; 2.0 ± 0.05 lambs/ewe) than AI using fresh (65%; 1.6 ± 0.1 lambs/ewe) or frozen (40%; 1.4 ± 0.14 lambs/ewe) semen. For AI animals the lambing rate and litter size were not significantly different when service was at a fixed time (50%; 1.5 ± 0.12 lambs/ewe) or at observed oestrus (56%; 1.5 ± 0.12 lambs/ewe). Carazolol did not permit complete cervical penetration in any ewe. Deep penetration of the cervix at AI was achieved in 33% of untreated (control) and 48% of carazolol treated ewes (P < 0.05). However, the proportion of ewes in which penetration of the cervix and semen deposition was greater than shallow was similar for control (82%) and carazolol (85%), and lambing rate and litter size were similar for both treatments. Over the three service methods, the lambing rate was 56% for control and 63% for carazolol (NS) and litter size was similar for both treatments. It was concluded that the carazolol treatment used prior to natural mating or AI in this experiment did not improve lambing rate or litter size in Kivircik ewes.     

Effects of melengestrol acetate and P.G. 600 on fertility in Rambouillet ewes outside the natural breeding season

The effects of melengestrol acetate (MGA) and P.G. 600 on ewe fertility outside the natural breeding season were evaluated. Rambouillet ewes were assigned to one of four groups: (1) control (C; n=92); (2) PG600 (n=86); (3) MGA (n=99); and (4) MGA+PG600 (n=92). A pellet with or without MGA (0.3mg/ewe/d) was fed at 0.15kg/ewe/d for 7d. On the last day of pellet feeding, ewes were given either saline or 5mL of P.G. 600 i.m. (400IU equine chorionic gonadotropin (eCG) and 200IU human chorionic gonadotropin (hCG)). Ultrasonography was performed between Days 20 and 25 of gestation for ewes that were mated during the first 6 d of the breeding period from the MGA (n=15) and MGA+PG600 (n=8) groups, and the number of luteal structures and embryos were counted. During the first 6d of the breeding period, MGA increased (P<0.05) the percentage of ewes that mated and conceived when compared to C and PG600 (24.2% vs. 3.3% and 10.5%, respectively). Relative to MGA, the mean (+/-S.E.M.) number of luteal structures per ewe was enhanced (P<0.03) in MGA+PG600 (1.53+/-0.13 vs. 2.38+/-0.42, respectively), however as pregnancy progressed, the number of embryos (1.5+/-0.13 vs. 1.8+/-0.16, respectively) and lambs born (1.3+/-0.15 vs. 1.5+/-0.27, respectively) did not differ. Treatment with MGA reduced (P<0.01) the interval from ram introduction to lambing relative to groups that did not receive MGA (168+/-0.8d vs. 171+/-0.6d, respectively). In conclusion, treatment with MGA increased the percentage of ewes conceiving early in the breeding period. Although P.G. 600 increased the number of luteal structures present per ewe, it did not significantly enhance ewe prolificacy.     

Genetic basis of variation in reproductive performance. I. Ewe lambs treated with fluorogestone acetate and PMSG in a controlled environment

This study involved records on fertility, prolificacy, multiple birth, fecundity, body weight and age at breeding of 2380 ewe lambs from 432 sires of three synthetic strains developed at the Animal Research Centre, Ottawa, Canada. Ewes were divided into two equal flocks which were bred to lamb alternately at 4-month intervals under an 8-month breeding cycle. Lambs were housed indoors, in a controlled environment, on expanded metal mesh floors in windowless barns and were bred in January, May and September at the end of a period of short days. Ewes that lambed were generally heavier and slightly older at breeding as were ewes that lambed to mating at the synchronised estrus. Though not significant, trends demonstrating seasonal differences in the heritabilities of all reproductive traits were observed. Paternal half-sib estimates showed fertility, prolificacy, multiple births and fecundity were non-heritable in ewes lambing to matings at the synchronized estrus. Heritability estimates for prolificacy and multiple birth were 0.22 and 0.13, respectively, in ewes lambing to matings at the synchronized plus follow-up estrus, suggesting that slow genetic progress can be achieved in these traits from selection. Heritability estimates ranged from 0.03 to 0.22 for body weight and from 0.28 to 0.54 for age at breeding. Ewes that lambed showed lower values than all ewes exposed. Phenotypic correlations between reproductive traits and either body weight or age at breeding were low and ranged from 0.04 to 0.09. There were higher estimates of genetic correlation of prolificacy (and multiple birth) with either body weight or age at breeding in ewes lambing to matings at the combined estruses. Indirect selection of ewe lambs based on age and body weight at breeding may be an effective alternative to direct selection for genetic improvement of prolificacy and multiple birth.     

Effect of rumen degradable bolus containing melatonin or progestagen pessary plus pregnant mare serum gonadotropin on estrus response and lambing rate in ewes

Two practical regimens designed to induce estrus and ovulation in ewes in late anestrus were compared. Forty ewes were given a soluble glass rumen bolus containing 150 mg melatonin on July 9 and were joined with two vasectomized rams on July 23 and with three fertile rams on August 6. A second group of 40 ewes was treated with an intravaginal progestagen pessary (60mg medroxy-progesterone acetate) on July 23. Following pessary removal after 12 d, ewes were given 750 IU of pregnant mare serum gonadotropin (PMSG). Five fertile rams were joined with these ewes 48 h after progestagen removal. Melatonin concentrations were determined in single blood samples collected in early afternoon of July 21. Mating dates, lambing dates and litter sizes were recorded. Date of mating was significantly later in ewes treated with melatonin compared with those treated with progestagen plus PMSG (P<0.0001). All ewes given melatonin were mated within 4 wk, and those on progestagen plus PMSG treatment within one day of fertile ram introduction. Thirty-four ewes (85%) allocated to melatonin treatment and 36 (90%) allocated to progestagen plus PMSG treatment lambed (P>0.05). Mean (+/-SEM) lambing date was later in melatonin-treated ewes (January 17+/-1.2 d) compared to those given progestagen plus PMSG (December 30+/-0.6 d; P<0.0001). Mean litter size was lower in melatonin-treated ewes (1.5+/-0.1) compared with those given progestagen plus PMSG (2.0+/-0.1; P<0.001). Plasma melatonin concentrations indicated that 9 of 40 ewes treated with melatonin had circulating melatonin concentrations of less than 16 pg/ml. It is concluded that under conditions that existed in this experiment, treatment with progestagen plus PMSG in late anestrus resulted in more synchronous mating and lambing and a higher litter size than that following administration of a soluble glass rumen-degradable bolus containing melatonin.     

Selection for reproductive rate in Rambouillet sheep: Estimated genetic change in reproductive rate

Rambouillet sheep were selected for high or low reproductive rate based on an index of reproductive rate, reproductive INDEX = dam's total lifetime lambs born/(age in years-1). Selected ewes were first born in 1969. A random bred control line was established from the remaining foundation ewes with the first ewes born in 1973. Genetic variances were estimated with REML procedures for reproductive index and number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing. Heritability of reproductive index was 0.26. Heritability for number of lambs born were 0.11 and 0.12 and for number of lambs weaned were 0.04 and 0.04 per ewe exposed for breeding and per ewe lambing, respectively. Breeding values for the reproductive index were estimated using the full animal model (BLUP) with the complete numerator relationship matrix on reproductive index, with fixed effect of year of birth of ewe and breeding values for number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing, estimated with the fixed effects of year of birth of ewe and age of ewe and the random effect of permanent environmental effect among repeated lambing records. Genetic change was estimated as the regression of breeding value for reproductive index and number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing on year of birth of the ewe. High and low lines both responded to selection for reproductive index as compared to the control line (P<0.01). The high line increased at a rate of b = 0.0134 ± 0.0006 reproductive index units and the low line decreased at a rate of b = − 0.0098 ± 0.0005 reproductive index units per year. Response to selection for reproductive index resulted in b = − 0.0074 ± 0.0007 and b = 0.0163 ± 0.0006 lambs per ewe exposed for breeding, and b = − 0.0041 ± 0.0002 and b = 0.0075 ± 0.0002 lambs weaned per ewe exposed for breeding in the low and high lines, respectively. There was a greater response to selection in the high line compared to the low line. These results indicated that the reproductive index did respond to selection.     

Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep

The efficacy of using a low cost system for delivering progesterone as part of an estrous synchronization protocol in sheep was evaluated. In experiment 1, Barbados Black Belly ewes (n=34) and ewe lambs (n=35; 37.5±0.9 kg) were assigned to be untreated, control animals (C), or to receive PGF(2α) on d0 (PG), or receive two injections of progesterone (200mg, i.m. each) on D -5 and on D -2.5, prior to PGF(2α), on D 0 (2PPG). Treatment with 2PPG increased the proportion of animals lambing to the first service (P<0.05), an effect that was greater in ewe lambs than ewes (treatment × parity; P<0.05). The interval from ram introduction to lambing and the mean lambing day was less (P=0.04) in the 2PPG-treated animals compared to control animals. In Experiment 2, lactating ewes from experiment 1 (n=61) 60-85 days postpartum were assigned within parity and number of lambs reared to remain nursing (S; n=29) or weaned (W; n=32) 3 weeks prior to treatment with the 2PPG protocol. There was no effect of treatment on the proportion of animals lambing to the first service or overall, interval from ram introduction to lambing and lambing interval. An 8-month lambing interval was observed in ewes in which estrus was synchronized regardless of physiological state. In conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus to reduce the lambing interval and maximize productivity in tropical breeds of sheep.     

Effect of insulin on feed intake and reproductive performance of well-nourished nulliparous ewes

Eighty-four nulliparous ewes were used to examine the effect of short-term insulin treatment on feed intake and reproductive performance. Following estrus synchronization, ewes were observed for estrus (= Day 0) and were penned individually beginning on Day 7. Ewes were fed twice daily and feed intake was recorded. On Days 9 through 13, ewes were treated s.c. with 1 IU/kg BW insulin (n = 44) or an equivalent volume of saline (n = 40). On Day 14, ewes were placed with fertile rams and number of ewes in estrus (bred) was recorded. Thirty days post-breeding, ewes were checked for pregnancy via ultrasonography. Feed intake and percentage of ewes in estrus did not differ between saline- and insulin-treated ewes. Similarly, neither pregnancy rate (69 +/- 8.7% vs. 80 +/- 8.1%, respectively) nor lambing rate (61 +/- 8.9% vs. 78 +/- 8.4%, respectively) differed between treatments. The number of lambs born per ewe was, however influenced by a breed-group effect (P < 0.0002). Romanov ewes had more (P < 0.001) lambs than the other breed groups in the study. Therefore, treating well-nourished, nulliparous ewe lambs with insulin did not increase reproductive efficiency, possibly because the ewes were already at a maximal nutritional and/or reproductive state.     

The effects of GnRH analogue (buserelin) or hCG (Chorulon) on Day 12 of pregnancy on ovarian function, plasma hormone concentrations, conceptus growth and placentation in ewes and ewe lambs

The objectives of this study were to determine the effect of GnRH analogue (buserelin) or human chorionic gonadotrophin (hCG, Chorulon) treatment on Day 12 of pregnancy on ovarian function, plasma hormone concentrations, conceptus growth and placentation in ewes and ewe lambs. After oestrus synchronization with progestagen sponges and eCG, all the animals were mated with fertile rams. Both ewes and ewe lambs (20 per treatment group) were given either normal saline or 4 microg GnRH or 200 IU hCG on Day 12 post-mating. Pre- and post-treatment plasma hormone concentrations were determined in seven pregnant animals per treatment group in samples collected 1h before and 0, 2, 4, 6, 8, 24, 48 and 72 h after treatment. Overall mean progesterone concentrations were higher (P<0.001) in ewes as compared with ewe lambs in saline-treated controls. GnRH or hCG treatment increased (P<0.001) mean plasma progesterone concentrations in both age groups, however, post-treatment concentrations were significantly (P<0.05) higher in ewes than in ewe lambs. Oestradiol concentrations were similar in the two control groups. In ewes, but not in ewe lambs, both GnRH and hCG treatments significantly (P<0.05) increased the mean oestradiol concentrations above pre-treatment levels. Moreover, post-treatment oestradiol concentrations in GnRH- and hCG-treated animals were significantly (P<0.05) higher than those in the saline-treated controls. LH release in response to GnRH treatment was greater (P<0.05) in ewes than in ewe lambs, whereas FSH release in ewes was less (P<0.05) than that of ewe lambs. The effects of GnRH or hCG on conceptus growth and placentation was determined at slaughter on Day 25. In ewes, GnRH treatment increased (P<0.05) luteal weight, amniotic sac width and length, and crown-rump length compared with controls, but had no effect on these parameters in ewe lambs. In ewes, hCG treatment also enhanced (P<0.05) luteal weight, amniotic sac width and length, crown-rump length, embryo weight and number of placentomes as compared with controls. In ewe lambs, there was no difference (P<0.05) between hCG and control groups in luteal weight, embryo weight and amniotic sac width but crown-rump length, amniotic sac length and the number of placentomes forming the placenta were greater (P<0.05). In conclusion, GnRH or hCG treatment on Day 12 of pregnancy can increase ovarian function, conceptus growth and placental attachment in ewes. However, these treatments were less effective in ewe lambs.     

Plasma hormone profliles and fertility in ewe lambs given progestagen supplementation after mating

Clun Forest ewe lambs (n = 124) were used to investigate the effects of post-mating progestagen supplementation on fertility. The animals were assigned to 1 of 3 three treatments: Group A (n = 41) served as the controls, Group B (n = 42) received 3 weekly injections of 6 mg of medroxyprogesterone acetate (MAP), while Group C (n = 41) was treated with intravaginal sponge containing 60 mg of MAP; all treatments were administered from Day 5 to Day 26 post mating. Supplementation did not increase the percentage of animals pregnant or those lambing: Group A, 72.2 and 66.6%; Group B, 57.5 and 50.0%; and Group C, 67.5 and 60.0%, respectively. Furthermore, there was no effect of supplementation on plasma progesterone, prolactin, cortisol, growth hormone, insulin, or glucose concentrations (P>0.05). However, pre- and post- mating hormone profiles differed significantly between the animals that lambed or aborted and the animals which were found to be barren at lambing. In the barren animals, progesterone concentrations were lower 4 days before and 9 to 33 days after mating (P<0.01), while overall prolactin concentrations were higher throughout the trial (P<0.01). But there was no difference between barren and fertile lambs in cortisol, growth hormone, insulin or glucose concentrations (P>0.05). These results indicate that progestagen supplementation does not increase the reproductive performance of ewe lambs. However, infertility is associated with reduced luteal function and increased prolactin concentration before and after mating.     

The effect of hCG treatment on Day 12 post-mating on ovarian function and reproductive performance of ewes and ewe lambs

The objectives of this study were to determine the effect of a single intramuscular injection of 200 IU hCG (Chorulon) on Day 12 post-mating on ovarian function and subsequent lambing performance in ewes and ewe lambs bred at synchronised oestrus during the breeding season and on the lambing performance of ewes induced to breed during late anoestrus. All animals were mated to rams at synchronised oestrus and on Day 12 post-mating given normal saline or 200 IU hCG.In Experiment 1, laparoscopic results showed that hCG treatment induced accessory corpora lutea in ewes (control = 0/7; hCG = 5/7) but not in ewe lambs (control = 0/7; hCG = 0/7).In Experiment 2, hCG treatment did not improve the lambing rate (control = 50; hCG = 57) or the litter size (control = 1.80; hCG = 1.96) in ewes (control = 100; hCG = 91). However, hCG treatment significantly (P > 0.05) improved the lambing rate (control = 29; hCG = 58; P < 0.05) in ewes conceiving at the first oestrus after treatment. hCG treatment (control = 42; hCG = 42) also failed to improve the lambing rate in ewe lambs (control = 48; hCG = 41).In Experiment 3, hCG treatment had no significant (P > 0.05) effect on the lambing rate (control = 72; hCG = 62) or the litter size (control = 1.59; hCG = 1.58) in ewes (control = 111; hCG = 115) induced to breed during anoestrus or on ewes returning to oestrus and conceiving after treatment (lambing rate: control = 86; hCG = 72; litter size: control = 1.44; hCG = 1.35). In conclusion, the data obtained in this study suggest that during the breeding season hCG may, by stimulating ovarian function, improve embryo survival in ewes conceiving at the first post-treatment oestrus. This effect, however was not observed in ewe lambs.     

Ovulation of aged follicles does not affect embryo quality or fertility after a 14-day progestagen estrus synchronization protocol in ewes

The aim was to examine the effect of ovulation of aged follicles on embryo quality and fertility in ewes. In Experiment 1, ewes (n = 39) received a prostaglandin analogue on Day 6 of the cycle and then received either a progestagen sponge from Day 6 to 20 after estrus (Single sponge) or a progestagen sponge on Day 6 that was replaced on Day 11 and 16 and removed on Day 20 (Multiple sponges). In a subgroup of ewes, the growth of ovarian follicles was characterised using ultrasonography. Fertile rams were introduced 48 hours after sponge withdrawal; we slaughtered the ewes on Day 5 of pregnancy and recovered the embryos. The mean age of the ovulatory follicles was greater in ewes that received a single sponge compared with multiple sponges (8.7+/-0.8 days, range 4 to 14, versus 4.5+/-0.7 days, range 3 to 6; P<0.05). However, the groups did not differ (P>0.05) in ovulation rate (2.4+/-0.3 corporal lutea per ewe) or the proportion of good quality embryos recovered (71 to 82%; developed to the early morula stage or further). In Experiment 2, ewes (570 in total) received treatments similar to those in Experiment 1 but were kept until lambing. Ewes that received a single sponge came into heat earlier (P<0.05) than those that received multiple sponges, but > or = 97% of ewes in all groups (P>0.05) were bred by 48 to 72 hours after ram introduction. There was no difference (P>0.05) between groups for the proportion of ewes that lambed to first service (80 to 86%) or the number of lambs per ewe (1.94+/-0.08 lambs). We conclude that when luteolysis occurs at the beginning of progestagen synchronisation, ewes will ovulate aged follicles, but that compared to shorter duration follicles, these follicles produce oocytes that are equally competent to be fertilised and develop into good quality embryos and full-term lambs.