Luteotropic effects of human chorionic gonadotropin administered 7.5 days after synchronous estrous induction in...

This study was conducted in ewes to assess effects of human chorionic gonadotropin (hCG) administration after imposing an estrous induction treatment regimen. Ewes (n = 115) were treated with a 60 mg medroxyprogesterone-intravaginal-sponge for 6 d plus 200 IU of equine chorionic gonadotropin (eCG) im and 37.5 μg d-cloprostenol im 36 h before sponge removal (Day 0). After natural mating, ewes having at least one corpus luteum (CL; n = 108) were administered either 1 mL of saline (G-Control; n = 53) or 300 IU of hCG (G-hCG; n = 55) on Day 7.5 after sponge removal (Day 0). Ovarian ultrasonography and blood collection were performed on Days 7.5, 13.5, 17.5, 21.5, and 30.5. Accessory CL (aCL) were observed in 81.5 % (G-hCG) and 0.0 % (G-Control) of ewes (P = 0.0001). Diameter, area, and volume of luteal tissue were greater (P < 0.05) in G-hCG from Day 13.5 to 30.5. Progesterone (P₄) concentrations were greater (P < 0.05) on Days 13.5, 17.5, 21.5 and 30.5 for ewes of the G-hCG group. Pregnancy percentage was similar (P = 0.25) between groups [47.1 % (G-control) compared with 60.0 % (G-hCG)], although total number of lambs produced by estrous synchronized ewes was greater (P = 0.005) in ewes of the G-hCG group (90.9 % compared with 66.0 %). In conclusion, hCG administration 7.5 days after sponge removal from Morada Nova ewes during the non-breeding season is an effective treatment to induce aCL formation, improve luteal tissue biometry and P4 concentrations, and to enhance the total number of lambs born.