Improved synchrony, conception rate, and fecundity in postpartum suckled beef cows fed melengestrol acetate prior to prostaglandin F2 alpha

Occurrence of estrus, conception rate, and fecundity were compared between postpartum suckled beef cows fed or not fed melengestrol acetate (MGA) before synchronizing estrus with prostaglandin F2 alpha (PG). One hundred thirty-three purebred Angus cows were stratified by age and days postpartum to one of two treatments. All cows received an injection containing 25 mg of PG; however, one group (MGA + PG) was fed 0.5 mg of MGA cow-1 d-1 for 14 d then received PG 17 d after the last feeding of MGA. The other group (PG) received only PG. Cows in both treatments that failed to exhibit estrus within 6 d after PG received a second injection of PG 11 d after the first injection was administered. Cows were checked for estrus from the first PG injection until 6 d after the second PG injection. Cows were inseminated with semen from a 3/4 Brahman bull 12 h after observed estrus. Cows were exposed to Angus bulls after the AI period. Conception date was determined by palpation per rectum and verified by calving date and calf phenotype. Differences in response variables were analyzed by chi-square. A greater proportion of cows (P 0.04) that were pretreated with MGA exhibited estrus after the first injection of PG (76%) than of cows that received only PG (60%). Total response did not differ between treatments after both injections of PG. Conception rate among cows that received a first service was higher (P 0.007) for the MGA + PG (88%) group than for the PG (67%) group, although the total number of cows that received a first service was not different between groups. Twinning rate was significantly higher (P 0.05) in cows that received MGA (15% vs 0%). Pregnancy rate was higher (P 0.01) in cows fed MGA (82%) than in cows that were not fed MGA (63%). Feeding MGA before PG resulted in more cows exhibiting estrus after the first PG injection and increased conception and calving rate among cows in estrus within 6 d after PG