Abstract
The effects of additive, dominance, additive by dominance, additive by additive and dominance by dominance genetic effects on age at first service, non-return rates and interval from calving to first service were estimated. Practical considerations of computing additive and dominance relationships using the genomic relationship matrix are discussed. The final strategy utilized several groups of 1000 animals (heifers or cows) in which all animals had a non-zero dominance relationship with at least one other animal in the group. Direct inversion of relationship matrices was possible within the 1000 animal subsets. Estimates of variances were obtained using Bayesian methodology via Gibbs sampling. Estimated non-additive genetic variances were generally as large as or larger than the additive genetic variance in most cases, except for non-return rates and interval from calving to first service for cows. Non-additive genetic effects appear to be of sizeable magnitude for fertility traits and should be included in models intended for estimating additive genetic merit. However, computing additive and dominance relationships for all possible pairs of individuals is very time consuming in populations of more than 200 000 animals.
Highlights
Genetic evaluations of dairy cattle are generally based on additive genetic models as either sire or animal models [8, 12]
Estimates of non-additive genetic variances, permanent environmental and residual variances are in Table III for all four fertility traits
Dominance genetic variances were greater than the additive genetic variance for age to first service, heifer non return rate, and interval from calving to first service
Summary
Genetic evaluations of dairy cattle are generally based on additive genetic models as either sire or animal models [8, 12]. Total genetic values of animals may contain non-additive components. Namely dominance and epistasis, are the result of interactions of alleles and loci. Interactions of alleles at the same locus result in dominance effects and interactions of two alleles at different loci result in additive by additive variation. Interactions of more than two alleles in different loci result in different levels of epistatic variations such as additive by dominance and dominance by dominance, and many others [19]. Non-additive genetic effects are not directly transmitted from parents to offspring, they are important for traits closely related to fitness or having low heritability [2]. If non-additive genetic effects are significant, ignoring them in genetic evaluation models could bias estimates of additive genetic effects
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