Recombinant equine chorionic gonadotropin for estrus and ovulation induction in ewes: effects on follicular growth,...

This study aimed to evaluate the effects of conventional purified equine chorionic gonadotropin (eCG) and recombinant eCG (reCG) on fertility in ewes during anestrus and transition to breeding season. In Experiment 1, 27 ewes received intravaginal devices (IVD) containing progesterone (P4) for 7 d and were allocated to the control, eCG, or reCG groups. At IVD removal, all animals were administered 250 μg cloprostenol, while eCG and reCG groups also received 400 IU eCG and 105 IU reCG, respectively. After IVD removal, the follicular diameter was evaluated at 24, 36, and 48 h, and serum P4 levels were measured on days 7 and 12. In Experiment 2, 391 ewes were allocated to the same groups described in Experiment 1 to evaluate estrus, pregnancy, and conception rates after natural mating. In Experiment 1, eCG (1.07 ± 0.27 mm/day; 100 %) and reCG (1.05 ± 0.27 mm/day; 88.9 %) treatments increased follicular growth (P < 0.05) and percentages of females that ovulated (P < 0.001) compared to those of the control (0.01 ± 0.27 mm/day; 0 % ovulation). Serum P4 concentrations of animals with a single corpus luteum (CL) after treatment (eCG: n = 5; reCG: n = 6) were higher in the eCG than in the reCG group (P < 0.001). In Experiment 2, the estrus rate was higher in eCG (95.27 %) and reCG (88.97 %) than in the control (78.22 %) (P < 0.001). No effect of treatments was observed for pregnancy (P = 0.99) and conception rates (P = 0.37). In conclusion, reCG effectively promotes follicular growth and induces ovulation in anestrus ewes. During the transition to the breeding season, reCG and eCG increased estrus rate, while pregnancy and conception rates remained unchanged compared with those of the P4 treatment.