PSV-A-1 - Estrus Response and Pregnancy Rates of Beef Cows Enrolled in Two Fixed-time Artificial Insemination Protocols, with or Without Pre-synchronization

Abstract: Pre-synchronization strategies with prolonged exposure to exogenous progesterone have the potential to alter estrus expression and improve fertility in beef cows. The objective of this study was to evaluate the estrus response and pregnancy rate of suckled beef cows enrolled in two fixed-time artificial insemination (TAI) protocols. A total of 1,216 cows (angus-crossed) at 10 locations across VA were enrolled in the study. Within location, cows were ranked by body weight, and days postpartum and randomly assigned to one of two treatments: 1) 7&7 (n = 610), cows were administered prostaglandin F_2α (PGF; 25 mg) and a controlled internal drug releasing (CIDR) insert [Day -14], an injection of GnRH (100 μg [Day -7]), PGF injection and CIDR removal [Day 0], and a second injection of GnRH concurrently with TAI 64 ± 2 h later [Day 2]; 2) 7-day CO-Synch+CIDR (7-day; n = 606), cows were administered GnRH (100 μg) and a CIDR insert [Day -7], PGF (25 mg) injection and CIDR removal [Day 0], and a second injection of GnRH concurrently with TAI 64 ± 2 h later [Day 2]. All cows received an estrus alert patch (ESTROTECT) on Day 0 and were evaluated for patch activation at TAI on Day 2. Pregnancy was diagnosed by transrectal ultrasonography between 45 and 65 days after TAI. The percentage of cows exhibiting estrus between Day 0 and 2 was greater (P < 0.001) for 7&7 compared with 7-day cows (72.8% and 55.9%, respectively). However, pregnancy rate to TAI was similar (P = 0.328) between treatments (63.8% and 61.1%, for 7&7 and 7-day, respectively). We conclude that suckled beef cows enrolled in the 7&7 TAI protocol had increased estrus expression, but similar pregnancy rate when compared with cows enrolled in the 7-day CO-Synch+CIDR TAI protocol.