Effect of tropically adapted sire breeds on preweaning growth of F-1 Anguscalves and reproductive performance of their Angus dams

The objective of this study was to determine the effect of tropically adapt ed sire breeds on preweaning growth performance of F-1 calves and on reprod uctive performance of their Angus dams. Angus (A) cows were bred in two con secutive years (1992 and 1993) by AI using semen from Brahman (B; Bos indic us; n = 10), Senepol (S; Bos taurus; n = 10), and Tuli (T; Sanga; n = 9) bu lls, A total of 82 B x A, 85 S x A, and 91 T x A calves were born. The stat istical model included the fixed effects of year, sire breed, calf sex, sir e breed x calf sex, and cow parity and the random effect of sire within sir e breed. Birth weight, weaning weight, 205-d adjusted weaning weight, PLUG from birth to weaning, and hip height at weaning were greater (P < .001) fo r B x A calves than for S x A or T x A calves. Greater differences were det ected between sexes for B x A than for S x A and Tx A (for all traits sire breed x calf sex, P < .05). Sire breed affected (P < .01) the percentage of unassisted calvings (B x A, 87%; S x A, 98%; and T x A, 100%) and tended ( P < .10) to affect the percentage of calves that survived until weaning (B x A, 90%; S x A, 94%; and T x A, 98%). Sire breed of calf did not affect (P > .10) length of gestation, and sire breed did not affect the interval fro m calving to first observed estrus or pregnancy in Angus dams. These result s demonstrate that preweaning growth performance of B x A calves was greate r than that of either S x A or T x A calves. However, use of Brahman sires on Angus darns led to calving problems and tended to reduce the percentage of calves that survived until weaning. Thus, heavier weaning weights of B x A calves would be an advantage for cow-calf producers marketing calves, bu t heavier birth weights and calving difficulty attributed to Brahman sires would be a disadvantage.