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

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 \u3c50% 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

Estrus response patches, timing for artificial insemination, and GnRH protocol in Split Timed AI beef cattle

An estrous-detection patch was used to determine the optimum timing for STAI and the necessity of GnRH at STAI on a 7-day CO-Synch+CIDR protocol. Crossbred beef cows (n=216) were stratified into the following treatment groups: CTRL=TAI (n=67) at 72 h post CIDR removal, or TRT=STAI (n=149) at 72 or 84 h post CIDR removal. All females received GnRH (100 mcg) plus a CIDR on d0, PGF2α, CIDR removal, and an Estrotect estrous-detector patch on d7. At 72 h post-CIDR removal, a patch score was assigned (PS150% removed) to all females. Cows in the CTRL group were administered a second GnRH (100 mcg) at 72 h TAI. Cows in the TRT group with PS2 were not administered GnRH. At 84 h, the remaining TRT group cows were given a second PS; cows with PS1 received a GnRH (100 mcg), and cows with PS2 were not administered. Results: The TAI pregnancy rates were similar (P=0.81) between the CTRL (45.6%) and TRT (44.8%) groups. Pregnancy rates tended to be higher (P=0.07) for cows with PS2 (50.3%) than for those with PS1 (29.4%). However, by extending TAI to 84 h in unresponsive cows, 82.0% of TRT cows did not receive a second injection of GnRH at TAI. It was concluded that the estrous detector patches reduced the percentage of cows that required GnRH at TAI without compromising pregnancy rates. The estrous detector patches significantly reduced the number of cows that received a second GnRH injection at TAI. Keywords: Split-time artificial insemination; STAI; GnRH; Beef cattle; heat detector

The effects of intramuscular or intravenous injections of gonadotropin releasing hormone at fixed-time artificial insemination on pregnancy rates of Bos indicus beef cows

The effect of an intramuscular versus intravenous administration of gonadotropin releasing hormone (GnRH) at fixed-time AI (FTAI) on the pregnancy rates of crossbred Bos indicus beef cows was evaluated. Pluriparous nursing calv cows (n=120) were synchronized as follows: d 0 cows received a 2.0 mg injection of estradiol benzoate (EB) and insertion of a controlled intravaginal progesterone releasing device containing 0.558 g of progesterone, d 8 removal of the progesterone device , a 0.15 mg injection of prostaglandin F2α (PGF), a 1.0 mg injection of EB, and 400 IU injection of equine chorionic gonadotropin. Fifty-four hr after PGF, all cows were exposed to FTAI and a 0.084 mg injection of GnRH was administered either via Vena caudalis (n=60), or via Longissimus dorsi (n=60). Cows were inseminated with the same sire and by a single AI technician. Pregnancy was determined by the transrectal ultrasonography on d 40 after AI. Cows receiving the intravenous administration of GnRH had higher (P = 0.04) pregnancy rates than the cows receiving the intramuscular injection of GnRH (65 vs 46.6%, respectively). It was concluded that the intravenous administration of GnRH at the time of AI improved the pregnancy rates of crossbred Bos indicus beef cows submitted to FTAI