The use of steroid hormones in superovulation of Nelore donors at different stages of estrous cycle.

Abstract The objective of the present study was to evaluate the superovulatory response and ova/embryo recovery from Nelore donors following treatment with a controlled internal drug releasing device and estradiol benzoate (CIDR-B program) at different stages of the estrous cycle. The control group (TI; n =40) received a standard superovulation protocol with females of this group being between days 9 and 12 of the estrous cycle (estrus = day 0). The donors that received a CIDR-B program containing 1.9 g progesterone and an intramuscular injection of estradiol benzoate (2 mg) were at day 0 (TII; n =30), between days 2 and 6 (TIII; n =30), days 7 and 12 (TIV; n =30), days 13 and 16 (TV; n =30) and days 17 and 20 (TVI; n =30) of the estrous cycle. Superovulation was induced with 400 IU of p-FSH, divided into eight decreasing doses (80/80; 60/60; 40/40; 20/20) at intervals of 12 h. The donors received PGF2α (Cloprostenol) 48 h after beginning the treatment and CIDRs were removed 12 h later. Artificial inseminations (AI) were performed 12 and 22 h after the initiation of estrus and embryos were collected 7 days after AI. The mean numbers (±S.E.M.) of total ova and embryos, viable (transferable) and degenerated embryos were 14.2±11.3, 7.4±6.9 and 3.2±3.5 (TI), 13.3±10.4, 7.1±6.2 and 3.3±4.3 (TII), 13.5±7.0, 8.1±6.7 and 2.3±3.0 (TIII), 17.4±9.9, 9.4±6.9 and 4.0±4.4 (TIV), 16.9±8.8, 9.8±8.1 and 2.7±2.5 (TV) and 13.0±7.8, 7.2±6.9 and 2.3±2.5 (TVI), with no significant differences ( P ≥0.05) among groups. Pregnancy rates of 67.1% (TI; n =86/128), 60.8% (TII; n =59/97), 62.5% (TIII; n =73/115), 64.1% (TIV; n =84/131), 72.3% (TV; n =81/112) and 60.6% (TVI; n =63/104) were obtained with embryos transferred from these collections and did not differ significantly ( P ≥0.05) among groups. The results of the present study allow us to conclude that a combination of steroid hormones may be used prior to superovulation in Nelore donors, at any stage of the estrous cycle without affecting the efficiency of embryo transfer programs.