Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate and PGF2α

Abstract A total of 402 two suckled postpartum beef cows at 2 locations (CSU and ECRC) were utilized in 3 trials to evaluate the effectiveness of a combination melengestrol acetate (MGA)-PGF 2α estrus synchronization system in spring-calving cows. The cows were allocatted by days post partum, body condition score (1 = emaciated;9 = obese), sire breed, and dam age at the beginning of treatment to 1 of 2 treatments within location and trial: MGA-PGF 2α (0.5 mg MGA/head/d for 14 d with 25 mg of PGF 2α injected 17 d after MGA withdrawal), and unsynchrpnized controls. All cows were observed for estrus at 12-h intervals for at least 5 d post injection. Cows observed in standing estrus were inseminated 12 to 18 h later. There was a location effect on response to treatment that was attributed to differences in body condition score between locations so data were analyzed within a location. Body condition score at the CSU location was 5.7 compared with 4.0 at the ECRC location. The CSU MGA-PGF 2α treated cows had higher (P 2α treated (31.6 and 21.4%, respectively) cows compared with that of the ECRC controls (11.9 and 8.5%, respectively). The CSU MGA-PGF 2α treated cows had higher (P 2α treated cows and ECRC control cows. The MGA-PGF 2α estrus synchronization system appears to contribute to pregnancy early in the breeding season in postpartum beef cows, although its effectiveness is limited by cow body condition.