PS1-2. Inclusion of Dominance Effect in the Single- and Multi-trait GBLUP Models for Saturated, Mono and Polyunsaturated Milk Fatty Acids from Canadian Dairy Cows.

Abstract Main nutritional components of bovine milk fat are fatty acids (FA) that are grouped based on the length of the carbon chains, and degree of unsaturation. Milk fat is composed of around 70% of saturated FA (SFA), 25% monosaturated FA (MUFA), and 5% polyunsaturated FA (PUFA). Some groups of dietary FA are linked to cardiovascular disease risks, whereas others are suggested to be beneficial to human health; therefore, dairy industry focus on the optimization of fatty acids in the milk production for the human health. Over the past two decades, advances in high-throughput sequencing technologies provide SNP markers for improvement of the complex (fatty acids) traits in genomic selection. The objective of this study is to compare the predictive ability of the single and multi-trait Bayesian GBLUP models including dominance effect for genomic selection of MUFA, PUFA and SFA traits by using 76,299 genotyping-by-sequencing-generated SNP markers from 695 Canadian Holstein dairy cows. The package BGLR with Multitrait function in R language was used to obtain heritability estimates and genetic correlations between MUFA, PUFA and SFA traits. Canadian Holstein cows were randomly clustered into 10-fold cross-validation to quantify the correlations between actual and predicted (without the individual's data) performance from single- or multi-trait GBLUP genomic prediction models. Additive and dominance heritability estimates from multi-trait GBLUP were 0.21, 0.26 and 0.21; and 0.18, 0.23 and 0.19, whereas the single-trait GBLUP estimates were 0.22, 0.28 and 0.23; and 0.23, 0.24 and 0.24 for MUFA, PUFA and SFA traits, respectively. Additive and dominance heritability estimates from multi-trait GBLUP models were lower than those form single-trait GBLUP models. Genetic correlations of 0.38 between MUFA and PUFA, -0.98 between MUFA and SFA, and -0.53 between PUFA and SFA from multi-trait GBLUP model indicated the positive genetic association between MUFA and PUFA, and the negative genetic associations between MUFA and SFA, and between PUFA and SFA. The lower heritability estimates from multi-trait GBLUP model could be resulted from the negative genetic associations between SFA and MUFA, and between SFA and PUFA. The prediction abilities of single-trait GBLUP with dominance effect (0.479, 0.807 and 0.505) and multi-trait GBLUP with dominance effect (0.472, 0.805 and 0.498) in cross-validation data sets were quite similar for MUFA, PUFA and SFA traits, respectively.