Estimation of genetic parameters and non-Mendelian genetic effects in Bos taurus-Bos indicus calves produced by embryo transfer

Abstract

Genetic parameters and non-Mendelian genetic effects were estimated from a data set on Bos taurus-Bos indicus calves produced by embryo transfer. The data set contained records for gestation length (GL), birth weight (BW), weaning weight (@, slaughter weight (SW) and hot carcass weight (HCW) on 590 3/4Angus-1/4Brahman, 3/4BrahrfianY4Angus backcross and F2progeny from nine mating strategies and bom in both fall and spring from 1991 and 1996. Data for these five traits were analyzed by single and multiple trait animal models including direct additive and recipient dam (matemal) effects as random effects, cross by gender and year by season as fixed effects and age at weaning, days on feed and age at slaughter as covariates. Variance components and heritabilities were estimated by using the Multiple Trait Derivative-Free Restricted Maximum Likelihood (MTDFRENM) computer program. Heritabilities from single and multiple trait analyses were 0.34 and 0.35 for GL, 0.37 and 0.37 for BW, 0.28 and 0.33 for WW, 0.58 and 0.61 for SW and 0.48 and 0.57 for HCW, respectively. The portion of variance due to matemal effects from single and multiple trait analyses were 0. 18 and 0. IO for GL, 0. 15 and 0. 12 for BW and 0. 3 5 and 0.27 for WW, respectively. Heritability estimates from the multiple trait analysis were higher than those from the single trait analyses and the proportion of variance due to matemal effects from the multiple trait analysis were lower than those from single trait analyses. High genetic correlations were estimated among slaughter-hot carcass weight (0.98), weaning-slaughter weight (0.90), weaning-hot carcass weight (0.81) and birth-weaning weight (0.87). The difference between reciprocal backcrosses was significant for GL, BW, WW, SW and HCW. Potential causes of reciprocal effects for these five traits were estimated using four regression variables associated with the effects of X and Y chromosomes and cytoplasmic inheritance and no effects were detected among 3/4Angus-1/4Brahman, 3/4Brahman-1/4Angus and F2 Bos taurus-Bos indicus calves. Since these data do not support the hypothesis of X or Y-linked inheritance as contributing to observed differences in reciprocal F, crosses, additional investigation will be necessary to explain the origin of differences between reciprocal backcrosses.