A Comparison of Two Estrus Synchronization Protocols Utilizing Progesterone Supplement 24 Hours before CIDR-G Removal in Sheep

Abstract

Two experiments investigated the effect of progesterone administration 24 h prior to intravaginal CIDR-G withdrawal using two protocols in two geographical locations and different breeds of sheep. Ewes in both experiments were administered with intravaginal CIDR-G either for 8 days (Expt. 1, n=36 thin tail mixed-breed ewes) in early April or for 12 days (Expt. 2, n=28 fat tail Awassi ewes) in late May. Half of the ewes in each experiment were assigned randomly one day before CIDR-G removal and given 25 mg P4 (P4-treated) and the second half were given saline solution and served as controls. Fertile rams were allowed with the ewes of both experiments immediately following CIDR-G removal (day0, 0h) and estrus was monitored at 6-h intervals for 4 days. Blood samples were collected for analysis P4 and LH levels. Estrus responses differed between the two experiments. P4 profiles during the period of CIDR-G insertion behaved the same way among ewes of both experiments, but levels differed (P < 0.05) on day 0 in response to P4 supplement. The preovulatory LH surge was greater among groups treated with P4 supplement than those that did not. In both experiments, the percentage of ewes exhibiting estrus was greater (P < 0.05) and intervals to estrus were longer (P < 0.05) in P4-treated than control ewes. In the 12-day protocol in Expt. 2, ewes treated with P4 supplement produced greater (P < 0.05) incidence of estrus, longer (P < 0.05) intervals to onset of estrus and LH surge and had higher (P < 0.01) magnitude of LH surge and pregnancy rate than controls and those of the 8-day protocol. In conclusion, P4 supplement 24 h prior to CIDR-G removal in a 12-day protocol can be used successfully to improve reproductive performance of ewes.