Short-term progestin estrus synchronization with timed insemination for beef heifers: CIDR vs. MGA

摘要

Recently, a new product, Eazi-Breed CIDR (a vaginal insert containing progesterone), was approved for estrus synchronization in beef heifers. In previous studies the CIDRhas produced excellent estrus synchrony, but it is more costly than the commonly used progestin, melengestrol acetate (MGA). Therefore, the objective of this study was to compare the CIDR to MGA in a shorter-termtimed breeding program. Seventy-seven commercial beef replacement heifers were assigned to one of two treatments, CIDR (n=38) or MGA (n=39). Each heifer in the CIDRtreatment group received a CIDR on day 1,which was removed on day 7. The MGA treatment group received MGA in the feedeach day from day 1 to day 6. All heifers inboth treatment groups received an injection of prostaglandin F2α (PGF) on day 7. Forty-eight hours after the PGF injection (day 9), all heifers received an injection of gonadotropin hormone-releasing hormone (GnRH) and were artificially inseminated. Pregnancy status was determined by ultrasonography 29 days post-breeding.A greater percentage (P=0.05) of heifers were pregnant in the CIDR treatment (55%) than in the MGA treatment (33%).