Genetic heterogeneity of residual variance for growth traits in American angus Cattle

Economic incentives have increased the demand for uniformity in beef production, making it a valuable phenotype for genetic studies. Genetic heterogeneity of residual variance suggests that variability around the mean may have a genetic component and could potentially respond to selection. However, evidence for genetic control of residual variance in beef cattle remains limited. The objectives of this study were to 1) investigate genetic heterogeneity of residual variances for birth weight (BW), weaning weight (WW), and yearling weight (YW) in American Angus cattle, and 2) compare models for genetic homogeneity (M1) versus genetic heterogeneity of residual variance, including a double hierarchical generalized linear model (DHGLM, M2) and a genetically structured environmental variance model (M3). A total of 75,000 BW, 74,975 WW, and 49,803 YW records were analyzed. Genetic parameters were estimated using average information restricted maximum likelihood for models M1 and M2, whereas model M3 employed Markov chain Monte Carlo within a Bayesian framework. We found evidence of genetic variation in residual variance for all traits, although the heritability estimates for residual variance were low, ranging from 0.004 to 0.01. Estimates of the genetic coefficient of variation for residual variance ranged from 0.38 to 0.62 for BW, 0.09 to 0.25 for WW, and 0.07 to 0.25 for YW, indicating potential for selection to reduce variability. Genetic correlations between mean and residual variance were negative for BW (-0.48 in M2 and -0.49 in M3) and positive for WW and YW. These findings indicate that the implications of selection for uniformity are trait-specific. Body weight should be maintained within an optimal range, whereas selection for increased WW and YW may lead to greater variability unless residual variance is incorporated into selection decisions. Overall, our results indicate the feasibility of reducing variability through selection, representing a first step in integrating growth trait uniformity into breeding goals for beef cattle.