Abstract #443

# 443
Bee Synch for synchronization and fixed-time AI of Bos indicus-influenced cows: An update.
Gary L. Williams*1,3, Randy L. Stanko2, Marcel Amstalden3, 1Texas A&M AgriLife Research, Beeville, TX, 2Texas A&M University-Kingsville, Kingsville, TX, 3Texas A&M University, College Station, TX.

Synchronization methodologies that are successful in straight-bred English and Continental breeds have proven less successful in Bos indicus-influenced cattle, with fixed-time AI (FTAI) pregnancy rates of 35 to 40%. Because of these poor outcomes, few commercial cattlemen who utilize these types of cattle employ synchronization technologies and FTAI. Research has indicated that variation in the rate of maturation of the dominant follicle after CIDR removal in Bos indicus-influenced females is a major contributor to reduced pregnancy potential at FTAI. Herein, we provide an updated report on the use of a modification of the standard 5-day CO-Synch + CIDR protocol, the 5-day Bee Synch + CIDR (Bee Synch) which has been termed PG-5-Day + CIDR by the Beef Reproduction Task Force. The protocol was designed to eliminate mature corpora lutea at the onset of synchronization, thus reducing circulating concentrations of progesterone, minimize variation in the rate of follicle maturation, and improve FTAI pregnancy rates. Initial studies evaluated the 5-Day CO-Synch + CIDR protocol alone (n = 100; Trial 1) or in comparison with Bee Synch (Bee Synch, n = 133; 5-Day CO-Synch, n = 136; Trial 2) at one location with mature cows. Subsequently, Bee Synch was evaluated at 4 additional locations utilizing Braford, Brangus, and Nelore crossbred cows. The 5-d protocol involved insertion of a controlled internal drug releasing device (CIDR) and i.m. injection of GnRH (100 μg; Factrel) on d 0. On d 5, the CIDR was removed and cows were treated i.m. with prostaglandin F (PGF; Lutalyse, 50 mg). Cows were inseminated at 66–72 h after CIDR removal and treated with 100 μg GnRH. Bee Synch employed a similar sequence except that all cows were treated with 25 mg PGF at the time of CIDR insertion. Pregnancy rate to FTAI in Trial 1 (5-Day CO-Synch + CIDR) was 33%. In trial 2, Bee Synch markedly improved FTAI pregnancy rates compared with the standard 5-day protocol (51.8 ± 0.9 vs 40.9 ± 5.7%; P < 0.04). Cumulative FTAI pregnancy rates in cows (n = 702) treated with Bee Synch at 5 locations averaged 51.9 ± 3.1% (range = 40 to 59.3). Bee Synch appears to improve FTAI feasibility in Bos indicus-influenced cows.

Key Words: synchronization, Bos indicus-influenced, Bee Synch