Effects Of Season And Breed On Superovulation Of Ewes

Improvement of superovulation efficiency, which are always be affected by seasons, breeds, hormones and schedules together, could be achieved by methods modification based on exploration and summary of influential factors.The purpose of this paper was to investigate the effects of season and breed on superovulation in ewes, especially the quality and quantity of embryos.After estrus synchronization with CIDR, the Black Suffolk and Dorper ewes were superovulated with PMSG plus seven dosages decreasing FSH and served by hand-mating or artificial insemination. The viable morula and blastosysts were transferred to recipient ewes immediately.First, the Black Suffolk ewes were superovulated in May and Septmenber. Ewes superovulated in May owned much higher ovulation rate than September(16.8±6.4 and 10.2±6.1, respectively; P<0.01), while the viability rate was much lower compared with September(56.0% and 92.5%, respectively; P<0.01). There was no significant difference in the survival rate of transferred viable embryos(33.9% and 36.7%, respectively; P>0.05) and the number of offspring per donor ewe(2.1±3.1 and 2.1±2.6, respectively; P>0.05) in May and September. However, offspring/ova ratio of donor ewes superovulated in May was much lower compared with September(18.5% and 32.8%, respectively; P<0.01).Second, the Black Suffolk and Dorper ewes were superovulated together during spring. The mean number of ova recovered did not vary between Black Suffolk and Dorper ewes(11.0±7.1 and 14.3±6.7, respectively; P>0.05), while the mean number of viable embryos and the viability rate of Black Suffolk ewes were much lower than Dorper ewes(5.1±7.3 and 11.3±6.3, respectively; P<0.05; 44.3% and 79.1%, respectively; P<0.01). The survival rate of viable embryos transferred twin per ewe did not differ significantly between Black Suffolk and Dorper ewes(75.0% and 80.0%, respectively; P>0.05), neither did the all viable embryos(30.9% and 40.8%, respectively; P>0.05). However, a lower percentage of donor ewes with offspring was observed in Black Suffolk compared with Dorper(44.7% and 88.9%, respectively; P<0.05), and the offspring/ova ratio of Black Suffolk was much lower than Dorper for all donors ewes(13.7% and 31.0%, respectively; P<0.01) but not for donors withoffspring(24.6±13.3% and 31.9±16.2%, respectively; P>0.05). It was concluded that the superovulation of ewes but not the survival of transferred embryos could be affected by season and breed. The ovulation rate of Black Suffolk ewes was much higher in May, while the viability rate was much higher in September. The number of viable embryos and the viability rate was much higher in Dorper ewes than Black Suffolk ewes during spring.