Abstract
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 (P4), estrogen (E2), and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were quantified with RIA. Calves born to Brahman were smaller (P < .05) than calves born to Angus cows. Prepartum concentrations of P4 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 P4 on d 20 to 14 before calving than cows bearing heifer calves (sex of calf x period; P < .04). Prepartum E2 was influenced (P < .05) by the breed of dam x breed of sire x period interaction. The ratio of P4:E2 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.2+ f1p4
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