Estrus syncrhonization in ewes with prostaglandins at dif-ferent days post CIDR insertion

Objective: To evaluate the effect of prostaglandin F2α (PGF2α) application on days 0, 3 and 6 of the synchronized luteal phases on reproductive perfomance and its effect on progesterone concentrations of multiparous ewes. Design/methodology/approach: The experimental design was a completely randomized. Seventy-five ewes synchronized with control internal drug release devices (CIDR) for six days and 250 UI of equine chorionic gonadotropin (eCG) were used at device removal. The ewes were randomly distributed in three treatments in relation to the days of application of PGF2α (125 μg sodium cloprostenol): in the first group of ewes, PGF2α was applied at the time of insertion of the CIDR (D0, n=25); in the second group PGF2α was applied on day three of insertion of the CIDR (D3, n=25) and in the third group it was applied on day six, at the time of the withdrawal of the CIDR (D3, n=25). The presentation of estrus and the gestation rate were analyzed through the c2 test. The onset of estrus and prolificacy by a Tukey analysis of variance and comparison of means. The concentration of P4 was carried out using the mixed design procedure, which included fixed effects of treatment and day, and interaction of both. Results: Presentation and onset of estrus were different (P<0.05) between treatments due to the effect of the interval in the days of PGF2α application. The progesterone (P4) concentrations in blood serum showed differences during the synchronized luteal phase (D0: 4.8 ng mL-1; D3: 6.0 ng mL-1, D6: 8.8 ng mL-1). However, no differences were found in gestation rate and prolificacy due to the main effects. Limitations on study/implications: The application of 125 µg of PGF2α on different days of the synchronized luteal phase does not affect gestation rate and prolificacy. Nevertheless, presentation and onset of estrus were different, so it must be considered in laparoscopic artificial insemination programs. Findings/conclusions: The application of PGF2α during the synchronized luteal phase at short intervals showed better results at the end of treatment. The corpus luteum (CL) and CIDR increase P4 concentrations; which modifies the estrus response, and it has a positive effect in reproductive performance.