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

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.