Evaluation of line and breed of cytoplasm effects on performance of purebred Brangus cattle

Abstract

Substantial differences between reciprocally crossed Bos taurus x Bos indicus calves for birth, weaning, and yearling weights have been reported. To determine whether cytoplasmic inheritance is responsible for a portion of these differences, field records for birth and weaning weight (n = 7,353) and postweaning average daily gain (n = 2,746) from registered Brangus calves were analyzed. An animal model that included maternal effects was fit for each trait. Breed of cytoplasmic origin was fit as a fixed effect and coded as Angus, Brahman, or unknown. Cytoplasmic line within each breed of origin was treated as a random effect. Variance components for random effects were estimated using derivative-free REML procedures. Line of cytoplasm accounted for less than .002% of the phenotypic variance in all three traits. Estimates for cytoplasmic breed of origin effects were small in magnitude, and contrasts tested (Angus vs Brahman and Angus vs Unknown) were not significant (P > .10). Estimates of heritability of direct (maternal) effects were .36 (.20), .41 (.27), and .21 (.08) for birth weight, weaning weight, and postweaning average daily gain, respectively. Estimates of genetic correlations between direct and maternal effects ranged from -.27 for postweaning average daily gain to -.58 for birth weight. No evidence for breed or line within breed of cytoplasmic origin effects was detected in these data.