Influence of calf genotype on preweaning calf development and reproductive function in Brahman (Bos indicus) dams

Vita.Calves born to Brahman (B) cows and Angus (A), Brahman (B), or Tuli (T) sires were evaluated to determine sire breed of calf effects on preweaning calf traits and reproductive activity in the dams. Over 2 yr, 225 cow-calf records were used to determine gestation length, birth weight, postpartum interval, and weaning weight. For a single year (Year 2), 114 cow-calf pairs were used to determine peripartum cow endocrine profiles, linear calf measurements at birth and weaning, calf survival traits, preweaning growth, and testicular traits. Gestation lengths differed $(P < .01)$ between all calf sire breeds (284 (A), 288 (T), 293 $pm$ 1 d (B)). Birth weights were similar for AB, BB, and TB calves (30, 31, 29 $pm$.5 kg, respectively). At birth, AB and BB calves differed $(P < .01)$ in heart girth, hip height, shoulder to pin length, and cannon bone length; TB calves were similar in either AB or BB for each linear birth trait. Poor neonatal vigor and mortality rates were higher $(P < .05)$ in BB calves (26%; 13%) than in AB (3%; 0%) and TB (5%; 3%). Adjusted weaning weights were heavier $(P < .01)$ for AB calves (220 $pm$ 3 kg) than for TB (200 $pm$ 3 kg) and BB calves (197 $pm$ 3 kg). Heart girth and testicular size were greater $ (P < .05)$ for AB than in TB and BB calves at weaning. Body length was shorter $(P < .05)$ for BB calves than for AB and TB calves. All genotypes differed $(P < .05$) in weight:height ratio at weaning. Cows carrying AB fetuses had greater $(P < .01)$ prepartum estradiol concentrations than cows with BB and TB fetuses. Cows delivering TB calves tended to have lower postpartum 13,14-dihydro-15-keto-prostaglandin F$sb2alpha$ concentrations than cows delivering AB and BB calves. Postpartum intervals to estrus were shorter $(P < .06)$ for cows nursing BB calves (83 $pm$ 4 d) than for cows nursing AB (95 $pm$ 4 d) and TB calves (97 $pm$ 13 d). Angus-sired calves were superior to Tuli- and Brahman-sired calves for growth from Brahman cows. Except for greater neonatal survival, preweaning performance of TB calves was similar to BB calves. Brahman-sired calves were associated with longer gestations and shorter postpartum intervals