Pregnancy rates to fixed-time AI in Bos indicus-influenced beef cows using PGF2 with (Bee Synch I) or without (Bee Synch II) GnRH at the onset of the 5-day CO-Synch+ CIDR protocol. Academic Article uri icon


  • Objectives were to 1) characterize fixed-time AI (FTAI) pregnancy rates using the 5-Day CO-Synch+CIDR protocol in mature, suckled Bos indicus-influenced beef cows, 2) compare FTAI pregnancy rates in the latter to a modified version (5-Day Bee Synch+CIDR; Bee Synch I) that included treatment with prostaglandin F2 (PGF2) at CIDR insertion on Day 0, and 3) test the hypothesis that elimination of both GnRH-1 at the onset of synchronization and the double dose of PGF on Day 5 (Bee Synch II) would not reduce FTAI pregnancy rates compared to Bee Synch I. For Experiment 1-trial 1, Brahman x Hereford (F-1) cows (n=168) at least 40d postpartum (PP; r=40-92d) at the time of CIDR insertion were administered the 5-Day CO-Synch+CIDR protocol with FTAI at 72h after CIDR removal. Pregnancy rates to FTAI averaged 34.91.9%. In Experiment 1-trial 2, fall- and spring-breeding Brahman x Hereford (F-1) beef cows (n=269) were stratified by days PP and assigned randomly to receive either the 5-Day CO-Synch+CIDR (n=136) or Bee Synch I (n=133) protocol, with FTAI at 66h after CIDR removal. Pregnancy rate to FTAI was greater (P<0.05) in Bee Synch I (52.60.9%) than in the 5-Day CO-Synch+CIDR procedure (40.45.7%). For Experiment 2, 422 mature Braford, Brangus, Nelore x Brahman, and Brahman crossbred cows (Bos indicus proportion unknown) at 4 locations were treated with Bee Synch I, with FTAI at 66h. Overall FTAI pregnancy rate averaged 51.72.1%. Finally, from 2013 through spring 2018, we used a switchback design using fall- and spring-breeding herds to compare Bee Synch I (402 observations) to Bee Synch II (393 observations). Overall frequency of detected estrus at 66h using ESTROTECT breeding indicator patches was 57.22.4%, conception rates of those detected in estrus was 64.43.5%, and FTAI pregnancy rates averaged 52.32.4%, none of which differed between treatments. Moreover, pregnancy rates to FTAI in both treatments did not differ in cows synchronized between 40 and 80dPP but increased after 80dPP (P<0.05). Bee Synch II, which eliminates GnRH-1 and the double dose of PGF2 on Day 5, results in FTAI pregnancy rates essentially identical to Bee Synch I but reduces synchronization costs and avoids the need for off-label (double dose PGF2) drug use.

published proceedings

  • Theriogenology

author list (cited authors)

  • Williams, G. L., & Stanko, R. L.

citation count

  • 6

complete list of authors

  • Williams, GL||Stanko, RL

publication date

  • January 2020