Effect of timing of second prostaglandin F2α administration in a 5-day, progesterone-based CO-Synch protocol on AI pregnancy rates in beef cows》.pdf

Available online at Theriogenology 74 (2010) 1002–1009 Effect of timing of second prostaglandin F2 administration in a 5-day, progesterone-based CO-Synch protocol on AI pregnancy rates in beef cows a b, a a a W.D. Whittier , R.K. Kasimanickam *, J.F. Currin , H.H. Schramm , M. Vlcek a Department of Large Animal Clinical Sciences, Virginia Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 b Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99164 Received 14 December 2009; received in revised form 20 April 2010; accepted 25 April 2010 Abstract The objective was to compare the timed AI pregnancy rate of Angus-cross beef cows synchronized with a 5-d CO-Synch CIDR (a progesterone-releasing intravaginal insert) protocol and given two doses of PGF2 (PGF), with the first dose in conjunction with CIDR withdrawal on Day 5, and the second dose given either early or late relative to the first dose. All cows (N 1782) at 16 locations received 100 g of GnRH CIDR on Day 0. Cows received 25 mg of PGF concurrent with removal of the CIDR on Day 5, and were randomly allocated within locations to receive a second PGF either early (N 881; from 0.5 to 3.9 h) or late (N 901; from 4.5 to 8.15 h) relative to the first PGF treatment. On Day 8 (72 h after CIDR removal), all cows were inseminated and concurrently g