Influence of small doses of gonadotropin-releasing hormone following controlled internal drug-release insert removal on reproductive parameters in beef cattle subjected to a fixed-time artificial insemination protocol

ABSTRACT Heifers and cows that exhibit estrus before fixed-time AI have increased concentrations of estradiol and greater conception rates compared with those that do not. Our objective was to determine whether small doses of gonadotropin-releasing hormone following controlled internal drug-release insert removal would affect estradiol concentrations, estrus expression, or pregnancy success. Beef cattle (n = 247) were synchronized using the 7-d CO-Synch+CIDR protocol and assigned to 1 of 3 treatment groups (0 μg,10 μg, or 5 + 5 μg of gonadotropin-releasing hormone). Animals were observed for estrus, blood samples were collected, and animals were bred by appointment. Concentrations of estradiol were influenced by time (P