Evaluation of Estrous Response Patches as a Tool to Determine Optimum Timing for Artificial Insemination and if Gonadotropin-Releasing Hormone is Needed at Timed-AI in Beef Cattle

Abstract

Two experiments evaluated using an estrous-detection patch to identify animals that are in standing estrus at split-timed AI (STAI) and the necessity of a gonadotropin-releasing hormone (GnRH) injection at STAI on a 7-Day CO-Synch + CIDR protocol. In experiment 1 (n=216) and in experiment 2 (n=101), multiparous lactating crossbred beef cows were stratified by age, BW, BCS, and post-partum interval to 2 treatment groups: CTRL=timed-AI (TAI) at 72h post CIDR removal, or TRT=STAI at 72 or 84h post CIDR removal. All females received GnRH plus a CIDR on d0, prostaglandin-F2α, CIDR removal, and an Estrotect estrous-detector patch on d7. At 72h post-CIDR removal, a patch score was assigned (PS1 <50% removed; PS2 ≥ 50% removed) to all females. Cows in the CTRL group were administrated a second GnRH injection at 72h TAI. Cows in the TRT group with a PS2 were not administrated GnRH at TAI. At 84h, the remaining TRT cows were given a second PS and cows with a PS1 received a GnRH injection and cows with a PS2 did not. Blood samples for Progesterone concentration were collected on d-11 and 0 to determine percent of cows cycling. Data were analyzed using Proc Genmod with treatment and AI technician as fixed effects, sire as a random effect, and BW, BCS, age, and PPI as covariates. In experiment 1, TAI pregnancy rates were similar (P=0.81) between the CTRL (40.8%) and TRT (43.4%) groups. Pregnancy rates tended to be greater (P=0.07) for cows with a PS2 (50.3%) compared with a PS1 (29.4%). However, by extending TAI to 84h in unresponsive cows, 82.0% of the TRT cows did not receive a second injection of GnRH at TAI. In experiment 2, TAI pregnancy rates were similar (P=0.80) between the CTRL (32.3%) and TRT (38.6%) groups. Pregnancy rates were greater (P=0.04) for cows with a PS2 (70.6%) compared with a PS1 (19.4%). By extending TAI to 84h in unresponsive cows, 37.1% of the TRT cows did not receive GnRH at TAI. Using a heat-detector can reduce the percentage of cows that require GnRH at TAI without compromising pregnancy rates.