A Concentração de Progesterona e a Estação Reprodutiva Interferem na Dinâmica Folicular e na Fertilidade de Ovelhas Leiteiras

Background: The use of high and low doses of progesterone in vaginal pessaries directly interferes with the response of follicular dynamics in ewes specialized in dairy production. Within the season, greater ovarian activity is observed, and outside the breeding season, the high dose of progesterone favors conception rates, number of live born lambs and gestational corpus luteum size. This work evaluated the response of the follicular dynamics of dairy ewes in and out of the breeding season, during the six-day stay of the vaginal pessary containing high and low doses of progesterone. Materials, Methods & Results: The experiment was conducted within the breeding season in April/May and out of season in October/November, evaluating the ovarian response to the use of vaginal pessaries containing 60 or 120mg of progesterone during six days of permanence. of the device, 75µg of sodium cloprostenol and 400IU of eCG were applied to remove the pessaries and reincarnation 50 hours after removal. As a result, it was observed that the ovulatory follicle has a larger diameter inside the station with 5.95mm and outside the station with 4.98mm. The size of the dominant follicle on D0 of the protocol was 4.77mm inside the season versus 1.55mm outside and without the presence of a corpus luteum, showing seasonal anestrus. The time of ovulation after the removal of the pessaries occurred around 48.68h inside the season and 53.40h outside the season. As for the size of the CL, it was larger within the breeding season with 12.15mm against 11.45mm out of season. For the conception rate inside the station, 71.4% and outside 50% were obtained. Out of season with 60mg, 41.2% was obtained and with 120mg, 58.8% for conception rate. For the number of live-born lambs/ewe, within the season it was found 2.32 and outside the season 1.59. Discussion: Seasonality in sheep is a remarkable factor, and out of season the ovarian activity was in anestrus, with only small follicles without the presence of a corpus luteum. In-station FO emerged at 3.79 days after device placement and out-of-station at 4.02 days. The possible explanation for this is the sum of the device's progesterone, associated with the CL. The average period of ovulation happened around 48.68 hours inside the season, and outside the season this value was 53.40 days, this variation in sheep is already described, but the mapping in dairy sheep is the first study. The number of ovulations differed between the evaluated seasons and between the progesterone doses, which suggests a direct effect of the dose and the season on the number of ovulations. The conception rate in the breeding season reached a much higher value, since the ovarian activity and the presence of the CL on D0 make the female respond better to the protocol, a fact that can be observed with the largest size of the CL at 30 days. In the off season, the protocol with 120mg resulted in a higher conception rate, and a higher dose of progesterone better prepares the ovulatory wave of each cycle, providing better oocyte viability and, therefore, a higher conception rate in this period.