Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: Replacement of gonadotropin-releasing hormone with human chorionic gonadotropin

摘要: Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with at time of AI 1), would improve fertility a fixed-time (TAI) in suckled beef cows. In addition, effects on follicle dynamics, corpus luteum development, concentrations progesterone (P4) evaluated. Exp. 1, cows stratified by days postpartum, age, parity assigned randomly 2 × factorial arrangement 4 treatments: 1) received 100 µg CIDR insertion (d -7) 25 mg PGF(2α) removal 0), followed 64 68 h TAI plus second injection (CG; n = 29); 2) same as CG but insemination was replaced (CH; 28); 3) CG, -14) (HG; 4) HG, (HH; 29). Pregnancy rates 52, 41, 59, 38% for GG, GH, HH, respectively. Cows receiving (39%) place tended (P 0.06) have poorer pregnancy than those (56%). Pre-CO-Synch treatment increased ng/mL -7, < 0.02) concentration P4 decreased 0.001) size dominant 0 3, compared not treated -14. 2, based BCS, breed type, calf sex then (n 102) HG 103) treatments. Overall 51%, no differences detected between 0.05) percentage cycling -7 pre-CO-Synch controls. Therefore, pretreatment induction after initiation failed enhance rates, may reduce rates.