Long-term selection of layers in the presence of dominance

This contribution evaluates long-term genetic gain and variance in a layer breeding programme in the presence of dominance. Most nucleus breeding operations in animal breeding are based solely on additive genetic architecture, including the development of new breeding methods such as the optimal contribution selection (OCS). However, non-additive genetic effects such as dominance can have a significant effect on genetic gain. Here we explore the role of dominance in long-term selection of layers without and with optimisation. To this end, we have stochastically modelled a breeding program over 40 years in line with genetic parameters from the real data. We compared scenarios where the three correlated traits were influenced by either additive effects solely, or by additive and dominance effects. Each scenario included 20 initial years of traditional (BLUP) selection, followed by 20 years of either continuation of BLUP selection or switch to genomic (single-step GBLUP) selection. Furthermore, for each scenario, we compared truncation selection without and with minimum inbreeding mating and OCS. As expected, genomic selection delivered higher gain than the traditional selection, but also reduced more variance. Their efficiency of converting variance into gain was similar. In the long-term OCS maintained higher efficiency of converting variance into gain than the truncation or minimum inbreeding mating. We will further explore comparisons between additive and dominance scenarios to unravel the mechanisms that are driving the gain, how they influence the long-term variability, with the goal to provide general considerations for sustainable breeding of layers.