Evaluating heat detector patch response to determine gonadotropin-releasing hormone use at timed artificial insemination on pregnancy rates in beef cattle

This study evaluated pregnancy rates in response to heat detector patch activation and the fate of gonadotropin-releasing hormone (GnRH) at timed AI (TAI) in a 7-d Co-Synch-plus-controlled intravaginal drug release (CIDR) protocol in beef cattle. Nulliparous heifers (n = 75) and lactating cows (n = 371) from 3 locations (n = 35, 139, and 198) were stratified by age, BW, BCS, and postpartum interval to a control (CON) or treatment (TREAT) group. All females received GnRH plus a CIDR insert on d 0, prostaglandin F2α, CIDR removal, and an Estrotect heat-detector patch on d 7. Beginning 54 h (heifers) and 72 h (cows) post-CIDR removal, a patch score (PS) was given (1 = unremoved; 2 = 35 to 65% removed; 3 = > 65% removed or missing). All heifers and cows in the CON, regardless of PS, and TREAT with a PS 1 received GnRH at TAI; all TREAT heifers and cows with a PS 2 and 3 received no GnRH at TAI. No treatment by location interaction (P > 0.10) existed for TAI pregnancy rates; thus, data was pooled across location. Timed AI pregnancy rates were similar (P > 0.05) between the CON and TREAT groups for heifers (43.2 and 50.0%) and cows (62.7 and 59.7%). Pregnancy rates were similar (P = 0.22) among cows with a PS of 2 and 3 in both groups. Using a heat-detector patch to determine if GnRH is needed at TAI may be an option to reduce CIDR-based TAI protocol cost.