Synchronizing estrus during a short period with low dose of equine chorionic gonadotropin (eCG) in primiparous and multiparous ewes

Abstract

Objective: To evaluate the effect of reducing the synchronized luteum phase and of applying eCG on reproductive response variables and hormone profile in primiparous and multiparous ewes. Design/methodology/approach: The experimental design was completely randomized with a 2 x 2 x 2 factorial array. Eight-one ewes were divided by their reproductive activity: primiparous (n=38) and multiparous (n=43). The percentage of presentation of estrus and pregnancy were analyzed with a c² test. The estrus onset and duration for an analysis of variance and the Tukey test of comparison of means. The P₄ concentration was performed using the PROC MIXED procedure, which included fixed effects of the treatment and day and the interaction of the two. Results: The response in estrus presentation was not different between treatments, however; the onset and duration of estrus were affected by physiological state and the synchronized luteum phase. P₄ concentrations in serum were higher in primiparous ewes than in multiparous ewes. There were no differences in pregnancy rate or prolificity by principal effects. Limitations on study/implications: The estrus onset and duration varied by effects of the reproductive physiological status and the duration of the synchronized luteum phase (6 and 12 d), Therefore, it must be taken into account when artificial insemination is performed at a fixed time. Findings/conclusions: The combination of cronolone sponges with 100 IU eCG during short (6 d) are effective for the synchronization of estrous. The P₄ concentrations in serum were higher in primiparous ewes, but this was not determinant for increasing gestation and prolificity in treated ewes.