Evaluating the effects of a high-concentration dose of prostaglandin F2α in a 5-d CO-Synch + controlled internal drug release protocol on fertility in beef cows

摘要

Estrous synchronization is a useful management tool to facilitate the use of fixed-time artificial insemination (AI) and improve fertility in beef herds. Addition of progesterone (P ) in the form of a controlled internal drug release (CIDR) device between the initial gonadotropin-releasing hormone (GnRH) and PGF injections (e.g. 5- and 7-d CO-Synch + CIDR [5-d and 7-d protocols, respectively]) has been shown to improve synchrony of ovulation and overall fertility ( ; ). It has been hypothesized that prolonged exposure to P in the 7-d protocol may increase the incidence of persistent follicles and aged oocytes ( ). By reducing duration of CIDR exposure from 7 to 5 d, in the 5-d protocol, incidence of prolonged follicular dominance is decreased, thus improving oocyte quality and pregnancy response ( ; ; ). However, there is a limitation when the length of follicular dominance is shortened, as the success of synchronization relies on the ability of PGF to regress a newly formed corpus luteum (CL) by the time of AI.