Study On Improving The Effect Of Estrus Synchronization By Modulating Follicular Recruitment In Sheep

Estrus synchronization is key to batch production of sheep.Nowadays,estrus synchronization treatments need to do heat detection.In this study,follicle recruitment was induced to improve the consistency of follicle development and concentration of ovulation,providing the conditions for timed artificial insemination.It is hoped that this will reduce the workload and improve breeding efficiency by avoiding heat detection while ensuring pregnancy rate.120 Dorper × thin-tailed Han crossbred sheep were randomly and equally divided into 6groups and treated using different estrus synchronization treatments.Follicle diameters were measured by ultrasound at 12 h intervals until ovulation was complete,and timed artificial insemination protocols were developed according to the distribution of ovulation times,thus expanding the sample size and verifying the reliability of the protocols.The results were as follows.1.The 12 d progesterone sponge group treated with progesterone sponge for 12 days.The duration of ovulatory follicular wave was measured by B ultrasound.Results indicated: The recruitment period,selection period and dominance period of 12 d progesterone sponge group were 2.68±0.93 d,0.9±0.34 d and 0.75±0.25 d,respectively.Recruitment period is significantly different from selection period and dominance period(P<0.05).2.Based on the duration of ovulatory follicular wave in the 12 d progesterone sponge group.PMSG was injected 2 days before the removal of progesterone sponge.Results indicated: The rate of ewes with follicle diameter ≥3.5 mm in 12 d 300 IU PMSG group and 10 d 300 IU PMSG group was 25% and 85%,respectively,with significant difference(P<0.05).Therefore,PMSG injection 2 days before the removal of progesterone sponge is beneficial to improve the development consistency of ovulatory follicular wave.3.In order to obtain higher ovulation concentration,after 10 days of treatment of progesterone sponge,different doses of PMSG were used to induce follicular recruitment,and the next day after removal of progesterone sponge was combined with 500 IU h CG treatment.The distribution of ovulation times was measured.Results indicated: The distribution of ovulation times in 200 IU PMSG,300 IU PMSG and 400 IU PMSG groups were 36～72 h,36～72 h and 36～84 h,respectively.The maximum ovulation rate was 80%,65% and 50%,respectively,and all occurred 48～60 h after the removal of progesterone sponge.4.Different timed artificial insemination protocols were developed based on the distribution of ovulation times.271 Dorper × thin-tailed Han crossbred sheep were treated with timed artificial insemination.Results indicated: In 200 IU PMSG group,cervical insemination was treated twice at 36 h and 48 h,48 h and 60 h,and the pregnancy rates were 54.05% and76.34%,respectively,with significant difference(P<0.05).In conclusion,Dorper × thin-tailed Han crossbred sheep treated with progesterone sponge for 12 days,200 IU PMSG was injected 2 days before removal of progesterone sponge,and500 IU h CG was injected the next day after removal of progesterone sponge,which resulted in a higher concentration of ovulation.Combined with cervical insemination at 48 h and 60 h after removal of progesterone sponge,a higher pregnancy rate could be obtained.