A 2-year experiment was conducted to determine the effect of a single injection of prostaglandin after initiation of the breeding season on ewe estrous synchronization. Rambouillet ewes (n = 101; Year 1 = 52; Year 2 = 49) assigned to one of three treatments: untreated (CON); 12-d CIDR insert (CIDR); or 1 injection of prostaglandin at d 2.5 (1 PG) after rams were placed with ewes. Rams were placed with ewes at the time of CIDR removal (d 0) and remained with ewes during a 35-d breeding season. Both the CIDR- (94%) and 1 PG (73.5%) treatment groups had a larger number (P ≤ 0.01) of ewes bred in the first 5 d of the breeding season compared to ewes of the control (33%) group. As expected, CIDR-treated ewes had a shorter time to mating, than 1 PG-treated ewes and ewes of the control group had a longer interval to mating than both CIDR- and 1 PG-treated ewes (P ≤ 0.01). The number of lambs born per ewe and kg of lamb weaned per ewe was not different (P ≥ 0.31) among treatment groups. Additionally, there was no difference (P = 0.78) in net profit per ewe among treatment groups. Based on these data, utilizing a single injection of PG 2.5 d after initiation of the breeding season resulted in similar pregnancy rates at d 5 of the breeding season when compared with CIDR-treated ewes indicating the potential utilization of the 1PG protocol in a confinement setting as a viable method for estrous synchronization.
Keywords: Estrous synchronization; Reproduction; Sheep.
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