Novas abordagens para o controle do ciclo estral e ovulação de fêmeas ovinas

Abstract

Reproductive efficiency and profitability of sheep flocks are greatly benefited by the use of assisted reproductive biotechnologies, such as estrous cycle control treatments and fixed-time artificial insemination (FTAI). The first study aimed to review and discuss the main aspects of estrous cycle control protocols and their updates. Based on this review, it was observed that there is a great variety of treatments for estrus induction and synchronization, and that protocols based on progestogens and equine chorionic gonadotropin (eCG) currently provide the best results. The second study aimed to review the use of double artificial insemination (double AI) via the superficial cervical route, both after estrus detection and at a fixed time. It was observed that the results presented in the literature after double AI are contradictory. In addition, most studies did not use the estrus synchronization protocols and insemination doses that are currently used, and some studies used frozen semen via the superficial cervical route, which is not considered adequate. It is concluded that further studies are needed to evaluate the potential benefit of double FTAI in current AI programs. The objectives of the third study were to evaluate the effect of double FTAI, the efficacy of the 125 µg dose of cloprostenol to induce luteolysis, and to determine the serum concentration curve of human chorionic gonadotropin (hCG) after intramuscular (i.m.) application. In Exp. 1, ewes received intravaginal device (IVD) containing medroxyprogesterone acetate (60 mg) for 7 days. At device removal, eCG (300 IU) and prostaglandin (PGF; 250 µg) were administered. All ewes were inseminated 54 h after IVD removal with fresh semen via the superficial cervical route, along with 4 µg of buserelin. At this time, the females were allocated to two groups: control (n=127) and 2AI (n=128). The 2AI group was inseminated again 14 h after the first FTAI. In Exp. 2, ewes received IVD for 6 days. At removal, the PGF 125 group (n=41) and the PGF 250 group (n=40) received 125 and 250 µg of cloprostenol i.m., respectively. The females were then exposed to natural mating. In Exp. 3, ewes (n=5/group) were treated with 100 (hCG100), 250 (hCG250) or 500 IU of hCG i.m. (hCG500) at the time of IVD removal, which remained for 14 days. Blood samples were collected 0, 6, 12, 24, 36 and 48 h after application. In Exp. 1, it was observed that double FTAI allowed 12 percentual points (p.p.) increase in pregnancy rate compared to single FTAI (P=0.04). In Exp. 2, the 125 and 250 µg doses of cloprostenol did not differ regarding the rates of estrus expression (81 and 65%, P=0.12), conception (67 and 69%, P=0.83) and pregnancy (54 and 45%, P=0.39). In Exp. 3, the three doses of hCG induced a serum concentration peak at 6 h after treatment, and it was possible to detect serum hCG levels at all time-points evaluated. It is concluded that double FTAI allows a significant increase in pregnancy rate, however, the cost-benefit of this approach should be evaluated in each situation, considering the need for additional farm work. The similar efficacy of the two doses of cloprostenol evaluated allows for a reduction in cost and volume to be administered to the animals. Finally, the hCG curves observed can help defining the doses to be used in studies evaluating the potential use of this gonadotropin for induction of final follicular growth or ovulation.