Effects of sire and dam on late-pregnancy conceptus and hormone traits in beef cattle.

Forty-six primiparous F1 heifers produced from mating Brahman (B), Charolais (C), Jersey (J), Longhorn (L), or Shorthorn (S) sires to crossbred cows were bred by AI to one of two Angus sires selected to produce high (H) or moderate (M) fetal growth. Dams were slaughtered at an average of 231 d of gestation. Daily blood samples were obtained from the dam on d 228 to 231 to determine serum estradiol, progesterone, and testosterone concentrations. Pelvic height was greatest (P < .05) in B, C, and L and pelvic width was greatest (P < .05) in S, C, and J dams, but pelvic areas did not differ (P > .10). Dams with greater hip height had larger pelvic areas (r = .45; P < .01). Intact fetuses from C and S dams were heaviest (P < .05), those from S dams had the greatest (P < .05) head width, and heart girth was greatest (P < .05) in fetuses from L dams. Fetuses from H sires were greater in weight (P < .01), body length (P < .01), and cannon circumference (P < .01). Dam differences were found in fetal heart weight (P < .01), trimmed placental membrane weight (P < .01), and average placentome weight (P < .05). Weights of eviscerated fetuses were greatest from C dams (P < .05). Placentome number was lowest (P < .05) in J dams, but J dams had the highest (P < .05) average placentome weight. Interactions between fetal genotype and breed of maternal environment were found for weight of eviscerated fetus (P < .05), body length, and heart weight (P < .01) and resulted from both magnitude and direction of change in the sire effect. The H sire increase in fetal weight was greatest in J dams, whereas B dams allowed expression of the fetal growth potential but at a lower level. Fetal trait interactions were also found for breed x sex and sex x sire (P < .05 to P < .01) and were due to the magnitude of differences expressed between the M and H sires. Serum testosterone concentrations were highest (P < .05) in B and L dams, dams gestating fetuses sired by the H sire (P = .08), and those with male fetuses (P < .01). We interpret these results to indicate that some maternal environments can suppress fetal growth, whereas others seem to complement the growth and allow maximum expression of the fetal genetic growth potential.(ABSTRACT TRUNCATED AT 400 WORDS)