Effect of breed, breeding season, eCG dose, and eCG application time on the estrous cycle of hair ewe lambs

Objective: To evaluate the effect of breed, breeding season, dose and application time of equine chorionic gonadotropin (eCG) on the estrous cycle and ovarian activity in hair ewe lambs.Design/methodology/approach: We studied 216 hair ewe lambs (62 Dorper, 69 Katahdin, and 85 Pelibuey) —91 in high breeding season and 125 in low breeding season—, who were synchronized with intravaginal sponges containing 20 mg of f luorogestone acetate (FGA), and intramuscular equine chorionic gonadotropin (eCG; 200 and 300 IU). The treatments are breed, breeding season, eCG dose, and eCG application time. We analyzed the presence of estrus using a logistic regression model, while for the interval to estrus and the ovulation rate we applied an analysis of variance, using a completely randomized design with a 2223 factorial arrangement with the PROC LOGISTIC and PROC GLM procedures.Results: The breed was a factor (P0.01) in the presence of estrus: Dorper ewe lambs presented 9.74 times more possibilities than Pelibuey. The interval to estrus was shorter (P0.05) in Dorper (29.50.9 h) and Katahdin (29.10.9 h) than in Pelibuey (34.80.9 h). The interval to estrus was lower (P0.05) when we applied 200 or 300 IU of eCG 24 h before the end of the protocol, than when we applied 200 IU of eCG at the time of progestogen withdrawal. The ovulation rate was only affected by breed (P0.05): it was higher in Pelibuey (2.40.1) than in Dorper (2.00.1) and Katahdin (1.90.1).Study limitations/implications: Conducting a second study would be advisable to complement this research. This would include the gestation stage of females and relate it to the ovulation rate, while also measuring the ovarian structures by means of ultrasound.Findings/conclusions: The main inf luencing factor on estrus and ovarian activity in hair ewe lambs synchronized with progestogens is breed.