The effects of ram exposure during progestagen oestrus synchronisation and time of ram introduction post progestagen withdrawal on fertility in ewes

Three experiments were undertaken to investigate the effect of a pre-mating ram exposure during progestagen synchronisation treatment on time of breeding, ovulation rate, embryo quality and fertility and any interaction with time of ram introduction for breeding post sponge withdrawal. Crossbred ewes in experiment 1a (n = 348), 1b (mule; n = 133) and 2 (n = 58) underwent a 12-14 days synchronisation protocol. Three days prior to sponge withdrawal ewes were divided into Control (ewes in continued isolation from rams) or +Ram (ram-exposed) groups. Rams were introduced to +Ram ewes and remained with ewes until sponge withdrawal. Ewes in experiments 1a and 2 received eCG at sponge withdrawal and were reintroduced to rams at either 36 or 48 h post sponge removal (PSR). In experiment 1b, ewes did not receive eCG and were reintroduced to rams at 24 h PSR. In experiments 1a and 1b time of breeding, date of lambing and litter size were recorded. In experiment 2, ewes were slaughtered 5 days post breeding, reproductive tracts flushed and corpora lutea, ova and embryos assessed. Fewer +Ram ewes were mated by 96 h PSR (P < 0.001) than Control ewes in experiment 1a but not when rams were introduced earlier in experiment 1b. In experiment 1a, ram introduction at 36 h PSR improved conception to first service compared to introduction at 48 h PSR (P < 0.01) in both +Ram and Control groups. In experiments 1a and 1b, +Ram ewes had reduced litter size caused by more single births (1a; P < 0.001, 1b; P < 0.01). In experiment 2, +Ram ewes had fewer corpora lutea than Control ewes (P < 0.001) but embryo quality was similar. However, more good embryos were produced when rams were introduced for breeding at 36 h compared to 48 h PSR (P < 0.001). We conclude that a pre-mating ram exposure during the synchronisation treatment reduced the number of ewes mated at and conceiving to the first service. This was partially overcome by introducing rams for breeding earlier (24 or 36 h compared to 48 h PSR) but the most dramatic decrease in fertility was due to a reduction in ovulation rate in the ram-exposed ewes.     

Effect of time of artificial insemination on fertility of progestagen and PMSG treated indigenous Greek ewes,during non-breeding season

A total of 2567 indigenous Greek ewes (Chios, Vlachiki and Vlachiki×Chios breeds) were used to determine the optimum time for insemination, following synchronization of oestrus with MAP-impregnated intravaginal sponges and PMSG during non-breeding season. Within each breed group, the ewes were divided into three subgroups and submitted to a double blind cervical artificial insemination 48 and 60 h (subgroup I), 60 and 72 h (subgroup II) and 48 and 72 h (subgroup III) after sponge withdrawal. From the results of the present investigation it can be concluded that the conception rate in the Chios island breed is better than that in the Vlachiki×Chios breed, with the latter being better than that in the Vlachiki breed. Using fixed time for AI, a better conception rate is obtained when applied 48 and 72 h after sponge withdrawal for Chios and Chios×Vlachiki breeds, while for Vlachiki breed a better conception rate is obtained when fixed AI is applied 48 and 60 h after sponge withdrawal.     

Induction of ovulatory estrus and fertility in non-cycling buffaloes with norgestomet during low breeding season

Field trials were designed to evaluate use of norgestomet treatment to induce ovulatory estrus in non-cycling buffalo cows and heifers during low breeding season. Twenty-five buffalo cows and 50 heifers under village management were given a 9-day treatment with a polymer implant containing 6 mg norgestomet with IM injections of 5 mg estradiol valerate + 3 mg norgestomet at the time of implantation and 600 IU PMSG when the implant was removed. Fifty animals served as controls without any treatment. Seventy-four treated animals showed estrus during the period between 36 to 80 hours after removal of the implant. Twenty-five buffalo cows and 40 heifers that could be further followed up were inseminated twice at 8-hour intervals, 12 hrs after induction of estrus with chilled semen by recto-vaginal method. Of these, 15 (23.1%) conceived, 9 (36%) among buffalo cows and 6 (15%) among heifers. Fourteen buffalo cows and 30 heifers that did not conceive manifested cyclic estrus at an interval of 22.4 and 20.6 days. The conception rate in the cyclic estrus was 57% and 23.3%, respectively, for buffalo cows and heifers. The overall conception rate over two inseminations was 46.2%, 68% in buffalo cows and 32.5% in heifers. In the control group, five (10%) showed spontaneous estrus and two (40%) conceived during the period of the experiment.     

Ram novelty and the duration of ram exposure affects the distribution of mating in ewes exposed to rams during the transition into the breeding season

This study compared the affect of short-term and continuous exposure to rams during the transition between anoestrus and the breeding season on the distribution of mating and subsequent lambing. Further, within ewes continuously exposed to rams we investigated the effect of replacing these rams every 17 days with 'novel' rams. During August (late anoestrus, Northern Hemisphere), multiparous, North of England mule ewes were allocated to one of four groups: SVR ewes were exposed to vasectomised rams for 24h on Day 0 (short term; n=109), RVR ewes were exposed to vasectomised rams for 24h on Days 0, 17 and 34 (short term; n=113); PVR ewes were exposed to vasectomised rams on Day 0 and remained with the same rams for the duration of the pre-mating period (continuous; n=104); NVR ewes were continuously exposed to vasectomised rams from Day 0 with the rams replaced with 'novel' rams every 17 days (continuous; n=113). Blood samples were collected from a subset of ewes (n=22 per group) to monitor progesterone. On Day 50, harnessed, entire rams were introduced for mating and raddle marks recorded daily for the first 17 days. The median date of mating occurred 1 day earlier in NVR ewes than PVR ewes (P<0.05). A synchrony score calculated from the blood sampled ewes showed that the distribution of mating was more synchronised in PVR and NVR ewes than SVR and RVR ewes (P<0.001). PVR and NVR ewes had an earlier onset of cyclic activity than RVR ewes (P<0.01). However, only NVR ewes differed from SVR ewes in this variable (P<0.05). Within ewes lambing to first service, the median date of lambing of PVR, NVR and SVR ewes occurred at least 2 days earlier than RVR ewes (at least P<0.05). Further, PVR and NVR ewes had a more compact distribution of lambing than SVR and RVR ewes (P<0.05) and lambing was more compact in NVR ewes than PVR ewes (P<0.05). In conclusion, ewes in continuous contact with rams prior to mating had a more synchronised distribution of mating and lambing than ewes given only short-term exposure to rams. This distribution of mating in continuous ram exposed ewes can be further enhanced by periodic exposure to novel rams.     

Effects of lactation status, progestogen and ram exposure on response to cloprostenol in ewes during the anestrous season

Progestogen pretreatment and introduction of rams were used to prepare 432 Rasa aragonesa ewes for synchronization of estrus with prostaglandin (PG) during anestrus. The experiment was a 3 x 3 x 2 factorial with lactation status, ram/progestogen treatment and treatment with pregnant mare's serum gonadotropin (PMSG; 250 IU) at injection of PG as main effects. At ram introduction (Day 0), ewes were dry (Group 1), weaned (Group 2) or suckling a lamb (Group 3). They received either norgestomet implants for 12 d (Days -12 to Day 0 (Group A), ram introduction for 12 d (Days 0 to 12) (Group B) or both (Group C). Half the ewes received PMSG with PG (100 mug Cloprostenol) on Day 12. Pregnancy rate was higher at first service in dry (Group 1; 42%) than in recently-weaned ewes (Group 3; 24% and Group 2; 31%; P<0.01). Occurrence of estrus and conception and pregnancy rates to first service were higher (P<0.01) in ewes previously exposed to rams (Groups B and C) than in ewes treated only with progestogen (Group A). There were no effects of PMSG, no interactions among the three variables and no differences in prolificacy (1.12 at first service).     

Synchronization of estrus with short- and long-term progestagen treatments and the use of GnRH prior to short-term progestagen treatment in ewes

The objective of the present study was to determine the efficacy of the synchronization of estrus using short- and long-term progestagen treatments in ewes at the onset of the breeding season, and to evaluate the effect of the exogenous GnRH administration immediately prior to short-term progestagen treatment on the reproductive performance. A total of 240 Tahirova cross-bred ewes, aged 18–24 months, and 40 rams, aged 2–4 years-old, were used in the trial. Ewes were divided equally into 3 groups (n = 80 per group). Intravaginal progestagen sponges containing FGA (30 mg) were inserted in the ewes for 7 d in the FGA1 (short-term) and GnRH treatment groups, and for 12 d in the FGA2 group (long-term). The ewes in the GnRH group received 10.5 μg busereline acetate i.m. at the time of sponge insertion. Tiaprost tromethamol (PGF_2α; 0.294 mg) and eCG (400 IU) were injected i.m. on the 6th day of progestagen treatment in the GnRH and FGA1 groups, and on the 11th day in the FGA2 group following sponge insertion. All ewes were hand-mated once at the detection of estrus. The estrous response, fertility rate, multiple birth rate and litter size recorded was 88.7, 87.3, 51.6% and 1.6 in the FGA1 group, 92.5, 71.6, 50.9% and 1.5 in the FGA2 group, and 96.2, 89.6, 71.0% and 1.8 in the GnRH group, respectively. No significant difference in estrous response between the groups was recorded, but the fertility rate in the FGA1 and GnRH groups was significantly (P < 0.05) higher than in the FGA2 group. The occurrence of multiple births and litter sizes were significantly (P < 0.05) higher in the GnRH group, compared to both the FGA1 and FGA2 groups, with the number of single lambs being significantly (P < 0.05) higher in the FGA1 (48.4%) and FGA2 (49.0%) groups than in the GnRH (29.0%) group. However, the differences recorded between any of the groups in terms of the number of twin and triplet lambs were insignificant. In conclusion, it can be said that estrous synchronization using the 12-d-FGA-eCG-PGF_2α regimen could be replaced with the 7-d-FGA-eCG-PGF_2α regime in sheep at the onset of the breeding season. However, the combination of GnRH with the latter regimen (7-d-GnRH-FGA-eCG-PGF_2α) increased the multiple birth rate and litter size in the ewes.     

Ovarian function in ewes at the onset of the breeding season

Transrectal ultrasonography of ovaries was performed each day, during the expected transition from anoestrus to the breeding season (mid-August to early October), in six Western white-faced cross-bred ewes, to record ovarian antral follicles > or = 3 mm in size and luteal structures. Jugular blood samples were collected daily for radioimmunoassay (RIA) of follicle-stimulating hormone (FSH), oestradiol and progesterone. The first ovulation of the breeding season was followed by the full-length oestrous cycle in all ewes studied. Prior to the ovulation, all ewes exhibited a distinct increase in circulating concentrations of progesterone, yet no corpora lutea (CL) were detected and luteinized unovulated follicles were detected in only three ewes. Secretion of FSH was not affected by the cessation of anoestrus and peaks of episodic FSH fluctuations were associated with the emergence of ovarian follicular waves (follicles growing from 3 to > or = 5 mm). During the 17 days prior to the first ovulation of the breeding season, there were no apparent changes in the pattern of emergence of follicular waves. Mean daily numbers of small antral follicles (not growing beyond 3 mm in diameter) declined (P < 0.05) after the first ovulation. The ovulation rate, maximal total and mean luteal volumes and maximal serum progesterone concentrations, but not mean diameters of ovulatory follicles, were ostensibly lower during the first oestrous cycle of the breeding season compared with the mid-breeding season of Western white-faced ewes. Oestradiol secretion by ovarian follicles appeared to be fully restored, compared with anoestrous ewes, but it was not synchronized with the growth of the largest antral follicles of waves until after the beginning of the first oestrous cycle. An increase in progesterone secretion preceding the first ovulation of the breeding season does not result, as previously suggested, from the ovulation of immature ovarian follicles and short-lived CL, but progesterone may be produced by luteinized unovulated follicles and/or interstitial tissue of unknown origin. This increase in serum concentrations of progesterone does not alter the pattern of follicular wave development, hence it seems to be important mainly for inducing oestrous behaviour, synchronizing it with the preovulatory surge of luteinizing hormone (LH), and preventing premature luteolysis during the ensuing luteal phase. Progesterone may also enhance ovarian follicular responsiveness to circulating gonadotropins through a local mechanism.     

Effect of melatonin on daily LH secretion in intact and ovariectomized ewes during the breeding season.

This study was conducted to find out whether daily LH secretion in ewes may be modulated by melatonin during the breeding season, when the secretion of both hormones is raised. Patterns of plasma LH were determined in luteal-phase ewes infused intracerebroventricularly (icv.) with Ringer-Locke solution (control) and with melatonin (100 microg/100 microl/h). Response in LH secretion to melatonin was also defined in ovariectomized (OVX) ewes without and after estradiol treatment (OVX+E2). Basal LH concentrations by themselves did not differ significantly before, during and after both control and melatonin infusions in intact, luteal-phase ewes. However, single significant (P<0.05) increases in LH concentration were noted during the early dark phase in the control and 1h after start of infusion in melatonin treated ewes. In both OVX and OVX+E2 ewes, melatonin decreased significantly (P<0.01, P<0.05, respectively) mean plasma LH concentrations as compared to the levels noted before the infusions. In OVX+E2 ewes, a single significant (P<0.05) increase in LH occurred 1h after start of melatonin treatment, similarly as in luteal-phase ewes. No significant differences in the frequencies of LH pulses before, during and after melatonin infusion were found in all treatments groups. In conclusion, melatonin may exert a modulatory effect on daily LH secretion in ewes during the breeding season, stimulating the release of this gonadotropin in the presence of estradiol feedback and inhibiting it during steroid deprivation. Thus, estradiol seems to be positively linked with the action of melatonin on reproductive activity in ewes.     

Climate factors affecting fertility after cervical insemination during the first months of the breeding season in Rasa Aragonesa ewes

This study was carried out to examine the impact of several climate variables on the pregnancy rate after cervical artificial insemination (AI) of Rasa Aragonesa ewes. Data were derived from 8,977 inseminations in 76 well-managed flocks performed during the first month of the breeding season (July to October). The following data were recorded for each animal: farm, year, month of AI, parity, lambing–treatment interval, inseminating ram, AI technician, and climatic variables such as mean, maximum and minimum temperature, mean and maximum relative humidity, rainfall, and mean and maximum temperature–humidity index (THI) for each day from day 12 before AI to day 14 post-AI. Means were furthermore calculated for the following periods around AI (day 0): ?12 to 0, ?2 to 0, AI day, 0 to 2, and 0 to 14. Logistic regression analysis indicated that the likelihood of pregnancy decreased when maximum temperature in the 2 days prior to AI was higher than 30 °C (by a factor of 0.81). Fertility was also lower for primiparous ewes and in multiparous ewes with more than five previous parturitions. Other factors with significant impact on fertility were flock, technician, inseminating ram, and a lambing–AI interval longer than 240 days. It was concluded that the 2 days prior to AI seems to be the period when heat stress had the greatest impact on pregnancy rate in Rasa Aragonesa ewes.     

A note on the effect of continuous ram presence on estrus onset, estrus duration and ovulation time in estrus synchronized ewes

During fall season, 18 multiparous Corriedale ewes were divided into two equal groups for the continuous (CON) and intermittent (INT) presence of a ram. Estrus was synchronized with fluorgestone acetate intravaginal sponges that were left 14 days, plus an injection of 200&mgr;g of a prostaglandin F-2alpha analog at sponge removal. Estrus was detected three times a day (at 6 a.m., 2 p.m. and 10 p.m.) by using rams with harnessess and markers. Ovulation time was determined by laparoscopy, starting 24h after estrus detection. Estrus onset was (mean+/-S.E.M.) 32.9+/-1.6 and 45.3+/-4.4h for the CON and INT groups, respectively (P<0.01). Estrus duration was 31.1+/-0.9 and 30.2+/-1.2h, for the same groups, respectively (P>0.05). Ovulation time and the interval from sponge removal to ovulation (ISRO) for the CON and INT groups was 29.0+/-1.5, 62.0+/-2.0, 26.7+/-1.3 and 72.0+/-4.2h, respectively. Ovulation time was not different (P>0.05), but ISRO was shown to be different between treatments (P<0.05). It is concluded that the continuous presence of a ram after sponge removal hastens estrus onset and reduces the interval between sponge removal and ovulation, without modifying estrus duration and time between estrus onset and ovulation.     

Medroxyprogesterone priming and response to the ram effect in Corriedale ewes during the nonbreeding season

The "ram effect" (RE) is an inexpensive technique that allows farmers to obtain out-of-season lambs. Five hundred and ninety-six Corriedale ewes were used in three experiments to determine the effectiveness of different medroxyprogesterone (MAP) treatments associated with the ram effect during the nonbreeding season. The aim of the first experiment was to evaluate the effectiveness of short-term (6-day) MAP priming. We obtained similar results in estrus incidence and fertility after using MAP sponges for 6, 9, and 13 days. In the second experiment, we compared the effect of sponges containing 20, 40, or 60 mg of MAP used in 6-day priming. Estrous behavior and fertility were not affected by dosage. In the third experiment, 2.5mg of MAP was administered in single treatments 0, 1, 3, or 5 days before the introduction of the rams. Medroxyprogesterone administration 1, 3, or 5 days before the introduction of the rams concentrated estrus in ewes 17 to 20 days later.     

The influence of ovarian status on response to estrus synchronization treatment in dairy goats during the breeding season

The influence of ovarian status (presence of a corpora lutea and follicles) on the times of the onset of estrus, LH peak and ovulation rate at a synchronized estrus was evaluated in 73 Alpine and Saanen cyclic goats. Does were treated for 11 d with 3 mg norgestomet implants or 45mg fluorogestone acetate (FGA) sponges. They also received 400 IU of PMSG and 50 μg of a PGF_2α analog on Day 9 of progestagen priming. Follicles (1 to 7 mm) and corpora lutea (CL) were counted by laparoscopy on Days 0 and 9 of progestagen treatment and 5 or 6 d after the synchronized estrus. Estrus was detected every 4 h from 16 to 60 h after the end of progestagen treatment using a vasectomized buck. The LH concentration was determined by radioimmunoassay (RIA) in blood samples collected every 4 h for 24 h beginning at the time of the onset of estrus. The number of follicles on Days 0 and 9 of progestagen treatment was not related to the time of the onset of estrus and occurrence of the LH peak or to ovulation rate. The number of CL on Day 9 influenced the time of occurrence of the LH peak but not the time of the onset of estrus. Thus, in does with 2 or 3 CL on Day 9, the LH peak occurred at 46.9 h after the end of progestagen treatment, and in does with 1 or 0 CL at 42.2 and 42.5 h, respectively, after treatment, suggesting that the number of CL at luteolysis is a factor in the variability of response after the synchronization of estrus.     

Ovarian function in ewes during the transition from breeding season to anoestrus

Transrectal ovarian ultrasonography was conducted in six Western white-faced ewes for 35 days from the last oestrus of the breeding season, to record the number and size of all ovarian follicles > or = 3 mm in diameter and luteal structures. Blood samples were collected once a day for estimation of serum concentrations of follicle-stimulating hormone (FSH), oestradiol and progesterone. Each ewe had five follicular waves (follicles growing from 3 to > or = 5 mm in diameter) over the scanning period. The duration of the growth phase of the largest ovarian follicles did not differ (P > 0.05) between waves, but follicular static and regressing phases decreased significantly (P < 0.05) after the decline in serum progesterone concentrations at the end of the last luteal phase of the breeding season. The intervals between the five follicular waves were: 9.2+/-0.4, 5.2+/-0.7, 8.3+/-0.8 and 5.8+/-0.7 days; the two shorter intervals differed (P < 0.05) from the two longer intervals. Using the cycle-detection program, rhythmic increases in serum FSH concentrations were detected in all ewes; the amplitude, duration and periodicity of FSH fluctuations did not vary (P > 0.05) throughout the period of study. The number of identified FSH peaks (7.8+/-0.5 peaks per ewe, per scanning period) was greater (P < 0.05) than the number of emerging follicular waves. Serum concentrations of oestradiol remained low (< or = 1 pg/ml) on most days, in five out of the six ewes studied, and sporadic elevations in oestradiol secretion above the non-detectable level were not associated with the emergence of follicular waves. The ovulation rate was lower than that seen during the middle portion of the breeding season (November-December) in white-faced ewes but the transitional ewes had larger corpora lutea (CL). Maximal serum concentrations of progesterone appeared to be lower and the plateau phase of progesterone secretion appeared to be shorter during the last luteal phase of the ovulatory season in comparison to the mid-breeding season of Western white-faced ewes. During the transition into anoestrus in ewes, the endogenous rhythm of FSH release is remarkably robust but the pattern of emergence of sequential follicular waves is dissociated from FSH and oestradiol secretion. Luteal progesterone secretion is suppressed because of fewer ovulations and diminished total luteal volume, but it may also result from diminished gonadotropic support. These season-related alterations in the normal pattern of ovine ovarian cycles appear to be due to reduction in ovarian responsiveness to gonadotropins and/or attenuation in secretion of luteinizing hormone (LH) occurring at the onset of the anovulatory season in ewes.     

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.     

Seasonality of ovulation and estrus, and the ram effect in poll dorset ewes

The effects of month on the proportion of Poll Dorset ewes expressing estrus and ovulating and on their ovulation rate when continually exposed to vasectomised rams and the effects of isolating the ewes from rams in winter/early spring were examined during 15 months in New South Wales, Australia. The percentage of ewes ovulating and their ovulation rate varied from 23% and 1.10 in November to an average of 99% and 1.85 in April and June, and the proportion of ewes expressing estrus followed a similar trend. Some ewes (6.8%) ovulated throughout the 15 months, and the average breeding season was 294 (SE = 6.1) days. Isolating ewes from rams in late winter/early spring significantly decreased the proportion of ewes ovulating from September to November, increased the proportion in December, but did not significantly alter ovulation rate. The variability in reproductive measures during spring offers scope for selection; with the ram effect, improvements in spring joining results from Dorset ewes are possible.     

Effects of time of PMSG and fixed-time GnRH injections on estrus incidence and fertility in physiologically different ewes pre-treated with progestogen-impregnated vaginal sponge during the nonbreeding season

A 2 × 2 factorial study for hormonal treatment was designed in 85 seasonally anestrous ewes with physiologically different status (nonparous, dry, and postpartum). All ewes were pre-treated with 60 mg of 6-methyl-17-acetoxy-progesterone (MAP) vaginal sponge for nine days and divided into four groups: Group I (22 ewes) — an i. m. injection of 600 i.u. pregnant mare's serum gonadotropin (PMSG) at the sponge removal (Day 0) and a single i.m. injection of 100 ug synthetic gonadotropin releasing hormone (GnRH) at 36 h after the sponge removal; Group II (21 ewes) — a PMSG injection at Day 0 and a saline injection at 36 h after the sponge removal; Group III (21 ewes) — a PMSG injection two days before the sponge removal and the GnRH injection at 24 h after the sponge removal; and Group IV (21 ewes) — a PMSG injection at Day -2 and a saline injection at 24 h after the sponge removal. The treated ewes were allowed to mate once with rams for five days after treatment. Estrus incidence and lambing rates were low (69.4% and 27.1%, respectively), probably due to the mating system and poor body condition of ewes used in the study. No effect of PMSG injection two days before with-drawal of MAP sponge and the fixed-time GnRH injection were observed in estrus incidence, fertility, and prolificacy. The present study indicates that the physiological status of ewes combined with management systems including feeding and mating would be important for out-of-season breeding with hormonal treatment.     

Effect of early and late exposure to estrual ewes on ram sexual performance classifications

This study was conducted to determine whether exposure of ram lambs to estrual ewes during their first autumn and again as adults just before serving capacity tests (SCT) affected the outcome of the sexual performance tests. Treatments were either early exposure of Polypay ram lambs (i.e., 7-8-mo-old rams with ewes for 17 d [n=30] or no early exposure [n=30]), and late exposure (i.e., 16-19-mo-old rams with estrual ewes for 3 d) or no exposure to estrual ewes in a 2x2 factorial arrangement. Three serving capacity tests were conducted immediately after the early exposure period for individual ram lambs that were exposed to ewes early. Three sham sexual performance tests (i.e., four ram lambs placed in test pens for 30-min without ewes) were conducted with ram lambs that were not exposed to ewes early. All rams were evaluated during nine 30-min serving capacity tests over a 2-mo period at 16-19 mo of age to determine sexual performance. Prior to serving capacity tests, one half of the rams from each early exposure treatment were exposed to estrual-induced ewes for 3 d. Specific sexual behaviors (e.g., sniffs, flehmens, foreleg kicks, vocalizations, mount attempts, mounts, and ejaculations) were recorded during serving capacity tests. Number of sniffs, flehmens, foreleg kicks, vocalizations, and mount attempts were summed without estimating the value of importance and analyzed as courtship behaviors. Sexual performance data were analyzed with Mixed model procedures for repeated measures. During serving capacity tests, the early exposed rams exhibited more courtships (40.3+/-8.0 versus 23.4+/-4.6; P<0.05; LSM+/-estimated SE), mounts (11.3+/-1.0 versus 7.7+/-0.9; P<0.01), and ejaculations (3.3+/-0.2 or 2.4+/-0.2; P<0.01) than rams not exposed to ewes as ram lambs, respectively. We conclude that early exposure of 7-8-mo-old ram lambs to estrual ewes improves sexual performance in serving capacity tests at 16-19 mo of age in most rams whereas, late exposure to estrual ewes for 3 d prior to serving capacity tests did not improve sexual performance scores.     

Effects of PMSG and ram contact on the reproductive performance of progestagen-treated ewes during breeding and anestrous seasons

The objective of this study was to evaluate the efficacy of combinations of PMSG treatment and ram contact on the reproductive performance of progestagen-treated ewes during three different times of the year, Febraury (early anestrus), July (late anestrus) and October (breeding season). A total of 109 multiparous Dorset ewes was used. Ewes were treated with intravaginal progestagen pessaries for 12 days, injected with 500 IU PMSG at pessary removal and either isolated from rams prior to mating (n = 12, February; n = 12, July; n = 8, October) or exposed to rams during pessary treatment (n = 17, February; n = 12, July; n = 8, October). A third treatment group (n = 18, February; n = 6, July; n = 8, October) received pessaries and ram exposure but no PMSG. An additional treatment of progestagen pessaries alone was included in October (n = 8). There were no differences among treatments in their ability to induce estrus at different times of the year, but incidence of estrus tended (P < 0.10) to be lower for PMSG treatment during the July breeding. During February, the use of pessaries with PMSG treatment increased (P < 0.05) conception and lambing rates, whereas ram contact was without any beneficial effects. The trend was reversed during July breeding, when ram contact increased (P < 0.05) fertility of progestagen-treated ewes compared with other treatment combinations. Pessaries alone were sufficient to attain acceptable levels of fertility and fecundity in October.     

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.     

Effect of long-term and short-term progestagen treatment on follicular development and pregnancy rate in cyclic ewes

The aim of this study was to evaluate the effect of the length of a progestagen treatment (12 d vs. 6 d) on follicular dynamics, estrus synchronization and pregnancy rate using medroxyprogesterone acetate (MAP) with or without an eCG dose at the end of MAP treatment. One hundred sixty Polwarth ewes were divided into four equal groups: long-term treated (LT, n=40); short-term treated (ST, n=40); long-term treated plus eCG (LTeCG, n=40); and short-term treated plus eCG (STeCG, n=40). Five ewes of each group were separated to undergo daily transrectal ultrasonography, and blood samples were taken for hormone determination. Until 96 h after sponge withdrawal the number of ewes in estrus was higher in both long-term-treated groups than in both short-term-treated groups but at the end of the observational period (144 h) no significant differences were found among groups. The pregnancy rate was higher in the ST group (87%) than in the other groups (LT, 63%; LTeCG, 67%; and STeCG, 58%; P< or =0.03). The ovulatory follicle emerged before sponge withdrawal in long-term-treated ewes (-3.8+/-0.4 d and -2.2+/-0.8 d for LT and LTeCG, respectively), whereas in short-term-treated ewes it emerges around sponge removal (0.4+/-1.1 d and 0.5+/-0.5 d for ST and STeCG, respectively; P< or =0.01). The ovulatory follicle in the LT group had a longer lifespan and attained a larger (P< or =0.05) maximum diameter than in the ST group. We conclude: a) that the lower pregnancy rate observed after long-term progestagen treatment was related to a slower follicular turnover that promoted the ovulation of persistent dominant follicles; (b) that short-term treatment resulted in a higher pregnancy rate probably due to the ovulation of newly recruited growing follicles; and (c) treatment with eCG had no advantage in association with long-term treatment and had a deleterious effect in combination with short-term treatment with MAP.