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.     

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.     

Control of estrus and ovulation in dairy cows

The efficiency of a synthetic prostaglandin analog (ICI 80996) for the control of the estrus cycle in dairy cows has been tested with and without simultaneous use of progestagen implants (SC 21009, Searle). Synchronization of estrus is closer after combined progestagen-prostaglandin treatments than after prostaglandins alone (78.7 % in estrus in 48h vs 60.2 % ; P<0.001).The percentage of cows not observed in estrus during the first 96h after the end of treatment was also lower after combined treatments (20.7 % vs 31.8 % ; P<0.05). The best estrus synchronization was obtained by injecting prostaglandin analog two days before implant removal (86 % in estrus in 48h and 14.0 % not observed in estrus within 96h).Fertility was studied in a field trial after one or two inseminations at a predetermined time for each treatment. A higher pregnancy rate was obtained with two inseminations after combined progestagen-prostaglandin treatment (49.1 %). This pregnancy rate differed significantly (P<0.05) from those obtained with one A.I. after the same treatment or two A.I. after the prostaglandin treatment but did not differ from the pregnancy rate obtained with one A.I. 80h after the second prostaglandin injection. The most important problem in dairy cows is the fall in pregnancy rate between 21 days and 6 months (19.7 to 35.1 % depending on treatment ; P<0.05).     

Induction of estrus and superovulation in seasonally anestrous ewes

The induction of estrus in 17 previously cycling nulliparous ewes, 9 to 10 months of age, was attempted with Medroxyprogesterone acetate (MAP) pessaries during the early anestrous period (March-April). Ewes were verified to be anestrous by the lack of estrous behavior in the presence of a vasectomized ram and by a radioimmunoassay for serum progesterone in two samples taken 7 days apart showing less than 1 ng/ml serum progesterone. Superovulation was attempted with injections of either FSH or FSH + LH. MAP vaginal pessaries remained in place for a period of 12 days and FSH was administered to all ewes (IM) at 12 hr intervals over a 3 day period; 5 mg was injected twice on day 11 after pessary insertion, followed by 4 and 3 mg injections twice daily on each succeeding day, for a total of 24 mg per ewe. Nine ewes were given 25 mg LH (IV) within 8 hrs after the onset of behavioral estrus in addition to FSH. Ewes were hand-mated to several rams at 12 hr intervals throughout the estrus period. Ovulation and fertilization rates were recorded for each ewe following midline laparotomy and embryo collection. All ewes were in estrus between 36 and 48 hrs after removal of the MAP pessaries. In ewes injected with FSH only, 8 of 8 ovulated with a mean ovulation rate of 6.0 +/- 4.4 and a fertilization rate of 70%. Nine of 9 ewes receiving both FSH + LH ovulated with a mean ovulation rate of 13.9 +/- 13.1 and a fertilization rate of 72%. Statistical analysis by Students t-test resulted in differences in number of ova recovered (P<.05) between FSH only and FSH + LH treated ewes and a trend towards increased ovulation rate in FSH + LH treated ewes. These results show that early seasonally anestrous ewes can be successfully induced and synchronized for estrus with MAP pessaries and the number of ova recovered is increased with the inclusion of LH in the superovulation regime.     

Estrus without ovulation in puberal ewes

In three groups of puberal sheep, one of young Merino ewes and one of Merino ewe lambs at Armidale, Australia, and one of Perendale ewe lambs at Hamilton, New Zealand, 20, 33 and 6.6% respectively of the animals failed to ovulate at their first estrus. Duration of estrus and intensity of overt estrous symptoms in these animals were the same as in their ovulating contemporaries. While the anovulatory estrus was followed by estrus with ovulation in most animals, many of the Merino lambs had a second anovulatory estrus and then went into anestrum. In some animals, failure of ovulation was followed by luteinization of a large follicle. In the Perendale lambs, the inter-estrous period following an anovulatory estrus was 15.9 days compared to 16.7 days in their ovulating contemporaries. The occurrence of anovulatory estrus in these three different groups of animals suggests that it is common in the first breeding season of young ewes. Lambing percentage probably is reduced below the expected level by the presence in the flock of ewe lambs that have had an estrus but not yet reached puberty.     

Relationship between doses of prostaglandin F2alpha and stages of the breeding season for synchronization of estrus and ovulation in ewes

Two experiments were conducted to compare estrous response to three doses (8, 16 and 24 mg) of prostaglandin F(2alpha) (PGF(2alpha)) administered by intramuscular injection to ewes between day 6 and 12 of the estrous cycle (Experiment I) and to ewes on unknown days of the estrous cycle during four different stages of the breeding season (Experiment II). In experiment I, a total of 41 ewes were treated with PGF(2alpha). The injection of 24 mg PGF(2alpha) resulted in a higher proportion of ewes exhibiting estrus (13 14 , 92.9%) within 5 days after treatment as compared to the other two doses (2 12 and 10 15 , for 8 and 16 mg PGF(2alpha), respectively). However, there was no significant difference for the proportion between 16 mg and 24 mg PGF(2alpha). In experiment II, PGF(2alpha) was given to ewes on the 3rd of February (early breeding season), the 28th of February (mid-early breeding season), the 10th of April (mid breeding season) and the 27th of May (late breeding season). These was a significant difference for the proportion of ewes exhibiting estrus between the early breeding season and the other three seasons (P < 0.05) but not for ewes ovulating. Throughout the breeding season, 16 mg PGF(2alpha) appeared to be slightly better than the other two doses (8 and 24 mg) although there was no overall difference in the estrous responses to treatment among the three doses. However, a significant difference in the proportion of ewes ovulating was found among the three doses of PGF(2alpha) (P < 0.05). Especially, 16 mg PGF(2alpha) was significantly superior to 8 mg (P < 0.01) and 24 mg (P < 0.05). It was considered that there was a complicated relationship between the doses of PGF(2alpha) and the stages of the breeding season for induction of estrus and ovulation in the ewe.     

Induction of ovulation in chronically hypophysectomized Booroola ewes

Booroola Merino ewes, with (F+; N = 17) and without (++; N = 13) a copy of the fecundity gene were hypophysectomized and 6 weeks later were given an i.m. injection of PMSG (high, medium or low dose) followed by hCG. The induced ovulation rates were observed laparoscopically. Ovulation rates were significantly higher (P less than 0.01) in Booroola F+ ewes than in ++ ewes (8.00 +/- 1.66 s.e.m. vs 3.62 +/- 1.10 respectively). This suggests that the high fecundity of the Booroola ewe may be due primarily to ovarian rather than pituitary factors.     

Induction of ovulation and cyclic activity in anestrous ewes with testosterone treated wethers and ewes

An experiment was conducted to evaluate the effectiveness of wethers and ewes treated with testosterone preparations to induce ovulation and breeding activity in anestrous ewes. The testosterone was administered three times at weekly intervals. Wethers and ewes treated with 105 mg testosterone propionate and wethers treated with 100 mg testosterone from testosterone cyclopentyl propionate were as successful as vasectomised rams in inducing ovulation and cyclic activity in ewes. Seven days after the last injection the concentrations of testosterone in peripheral bloods were not significantly different from that in the vasectomised rams. By day 28 the concentrations were significantly lower than in the rams. The testosterone preparations tested are suitable for the induction of male sexual behavior and are rapidly excreted by sheep.     

Serum LH peak and ovulation following synchronized estrus in goats

This study was aimed at comparing the temporal relationship between estrus, the LH peak and ovulation following estrous synchronization in goats using medroxiprogesterone acetate (MGA) or fluorogestone acetate (FGA). Twenty-four cyclic goats were randomly assigned to two treatments: MGA group (n = 12) that individually received a daily oral dose of 0.22 mg MGA for 12 days, and a FGA group (n = 12) treated for 12 days with intravaginal sponges containing 45 mg FGA. The goats from both groups were treated with a prostaglandin analogue (75 μg Cloprostenol i.m.) during the last day of their progesterone treatment. Estrous detection was carried out every 4 h after the end of the treatment, and blood samples for the determination of the serum LH concentrations collected at 2 h intervals for 24 h from the onset of estrus. Ovulation was detected with the aid of transrectal ultrasonography, performed every 4 h starting 15 h after the onset of estrus. All goats showed estrus. In the MGA group the onset of estrus occurred later and was more variable in relation to the end of treatment (86.7 ± 3.9 h), compared to the FGA group (44.4 ± 1.5 h; P < 0.01). The interval between the LH peak and ovulation was significantly (P < 0.05) longer in the MGA group (26.2 ± 1.1 h) than the FGA group (22.4 ± 0.8 h). There were no differences regarding the intervals from the onset of estrus to the LH peak (14.9 ± 1.8 and 15.3 ± 0.9 h) and to ovulation (40.1 ± 2.3 and 37.6 ± 0.5 h) for the MGA and FGA groups, respectively. The amplitude of the LH peak was not different between groups. It could be concluded that the timing of the LH peak and ovulation is not related to the end of treatment, but with the time of onset of estrus. The longer and more variable interval for estrous demonstration following MGA treatment, represents a serious limitation for its use in synchronization programs in goats, where mating is to be performed on a fixed-time basis.