Quantifying Dominance Variance to Enhance Genetic Evaluation and Prediction of Pre-Weaning Growth Traits in Dairy...

Dominance genetic effects, despite their recognized role in complex traits, are rarely included in livestock genetic evaluations. Using extensive phenotypic and pedigree data from 7537 dairy goat kids born between 2016 and 2023, we assessed the contribution of dominance variance to early growth traits through single-trait animal models fitted by the AI-REML algorithm in WOMBAT. The models combined additive, dominance, maternal genetic and maternal permanent environmental effects, and were evaluated using Akaike's Information Criterion (AIC), mean squared error (MSE) and Pearson's correlation between observed and predicted phenotypes (r( $y$ , $\hat{y}$ )). Incorporating dominance variance consistently improved model fit and predictive ability across traits, reducing residual variance by 13%-59% and increasing the accuracy of additive breeding values by up to 59%, without substantially altering the ranking of top animals. On average, dominance variance explained 30% of phenotypic variation, corresponding to 76% of the additive genetic variance. Dominance heritabilities for birth weight (BWT), weaning weight (WWT) and average daily gain (ADG) were 0.48 ± 0.06, 0.12 ± 0.03 and 0.32 ± 0.02, respectively, whereas additive heritabilities were lower (0.05-0.10). Genetic correlations differed notably between additive (0.59-0.66) and dominance (-0.33-0.41) components, highlighting the distinct contribution of non-additive effects. This study provides one of the first large-scale evaluations of dominance variance in dairy goats under commercial conditions. The results demonstrate that ignoring dominance can lead to underestimation of genetic variance and reduced predictive accuracy, underscoring the importance of modelling dominance effects in small ruminant breeding programs. These findings extend beyond a single breed, offering valuable implications for genetic evaluation strategies in dairy goats and other small ruminants.