INFLUENCE OF MATERNAL AND SERVICE-SIRE BREED ON SERUM PROGESTERONE AND ESTROGEN BEFORE CALVING AND PLASMA 13,14-DIHYDRO-15-KETO-PROSTAGLANDIN F2-ALPHA AFTER CALVING

Effects of breed of service sire and cow on birth weight and prepartum and postpartum endocrine function were studied in multiparous Brahman (n = 20) and Angus (n = 20) cows bred to Brahman or Angus bulls. Befo re calving, blood samples were collected on d 34 to 28, 27 to 21, 20 t o 14, and 13 to 7, and after calving, samples were collected from d 0 to 7. Progesterone (P-4), estrogen (E(2)), and 13,14-dihydro-15-keto-p rostaglandin F-2 alpha (PGFM) were quantified with RIA. Calves born to Brahman were smaller (P < .05) than calves born to Angus cows. Prepar tum concentrations of P-4 were greater in Angus cows and decreased mor e rapidly near parturition than in Brahman cows (breed of dam x period ; P < .03). Cows bearing bull calves had greater concentrations of P-4 on d 20 to 14 before calving than cows bearing heifer calves (sex of calf x period; P < .04). Prepartum E(2) was influenced (P < .05) by th e breed of dam x breed of sire x period interaction. The ratio of P-4: E(2) tended to decrease more in Angus than in Brahman cows near partur ition (breed of dam x period; P < .09). Postpartum PGFM tended to be i nfluenced (P < .08) by breed of dam x breed of sire; from d 3 to 5, Br ahman cows bred to Angus bulls tended (P < .08) to have greater PGFM t han Brahman cows bred to Brahman bulls or than Angus cows bred to Brah man or Angus bulls. On d 1 after calving, cows producing heifer calves tended(P < .09) to have greater PGFM concentrations than cows produci ng bull calves. Hormonal profiles before and after calving were influe nced by breed of service sire and cow, sex of calf, and sampling perio d.