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. Before calving, blood samples were collected on d 34 to 28, 27 to 21, 20 to 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-prostaglandin F-2 alpha (PGFM) were quantified with RIA. Calves born to Brahman were smaller (P < .05) than calves born to Angus cows. Prepartum concentrations of P-4 were greater in Angus cows and decreased more 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 the 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 parturition (breed of dam x period; P < .09). Postpartum PGFM tended to be influenced (P < .08) by breed of dam x breed of sire; from d 3 to 5, Brahman cows bred to Angus bulls tended (P < .08) to have greater PGFM than Brahman cows bred to Brahman bulls or than Angus cows bred to Brahman or Angus bulls. On d 1 after calving, cows producing heifer calves tended(P < .09) to have greater PGFM concentrations than cows producing bull calves. Hormonal profiles before and after calving were influenced by breed of service sire and cow, sex of calf, and sampling period.