Effect of stage of the estrous cycle at the time of initial exposure to rams on the ovarian activity of Pelibuey ewes

Abstract

Forty non-lactating, cyclic adult Pelibuey ewes were randomly divided into six groups. Estrus was synchronized within each group using intravaginal sponges and prostaglandin F2α injection at the time of the sponge removal. The sponges were inserted and removed on different dates in each group, but all the groups except the control one were first exposed to rams on the same date (July 17<sup>th</sup>), so that at the time of the first exposure the ewes were either on day 0 (group D0; n = 7), 3 (group D3; n = 7), 8 (group D8; n = 7), 12 (group D12; n = 7) or 14 (group D14; n = 7) of their synchronized estrous cycle. Thereafter the ewes of these groups remained continuously exposed to the males until all the females showed estrus. The ewes in the control group (CG; n = 5) remained isolated from all the males, except for 5-minute periods at the time of estrus detection, which was carried out three times a day. Progesterone concentrations were determined in plasma samples taken daily from two days before the initial exposure to the males until the onset of the next estrus. There were no differences in estrous cycle length between the groups exposed to rams and the control group (P > 0.05). The interval from the assumed onset of the estrous cycle (48 h after sponge removal) until the occurrence of luteolysis was not different between the control group and any of the groups exposed to the males. The interval from luteolysis to estrus was not modified by exposure to the males (P > 0.05). Estrus duration was shorter (P < 0.06) in the control group than in group D3. It is concluded that the exposure of cyclic Pelibuey ewes to males does not advance the time of luteolysis and does not affect the length of the estrous cycle. Therefore, the male effect does not synchronize the next estrus of cyclic Pelibuey ewes.