Additive and dominance effects of casein haplotypes on milk composition and quality in Norwegian dairy goats

The four casein loci – CSN1S1, CSN2, CSN1S2 and CSN3 – encoding for the four caseins are found clustered within 250 kb in chromosome 6 of the caprine genome. Additive and dominance effects of casein haplotypes within casein loci on milk composition and quality were studied. For the study, 1825 Norwegian dairy goats (745 bucks and 1080 does) were genotype for 38 SNPs within the entire casein region. Casein haplotypes were inferred within each of the four loci using BEAGLE. Phenotype measurements on milk yield and composition were obtained from Norwegian Dairy Goat Control recording system. Fixed additive and dominance effects of casein haplotypes were estimated using single trait mixed model combined with principal component analysis (PCA) to solve multicolinearity in the design matrix. Additive effects of haplotypes of the CSN1S1 locus were observed for protein and fat percentages, free fatty acids (FFA) content and somatic cell count (SCC) in milk. The most frequent haplotype of the CSN1S1 locus had negative additive effect on protein and fat percentage and increased the FFA content and SCC in milk. This haplotype also had negative dominance effects for protein, fat and lactose percentages and positive dominance effect for milk yield in kg. Some haplotypes of the CSN2 locus had effects on protein and fat percentages, milk yield and FFA content. Additive effects of haplotypes of the CSN3 were found for protein. The observed effects of casein loci haplotypes on economically important milk production traits indicate that there is an opportunity to select for specific haplotype as a tool to enhance selection response.