Effects of beta-casein and kappa-casein genotypes on milk production and composition in the Dairy Gir cattle

Abstract

Abstract This study aims to evaluate the effects of variants of the beta-casein and kappa-casein genes on milk production (P305) and milk composition (fat and protein) in Gir Dairy cattle, changing the selection of traits of economic importance, such as the A2 allele for beta-casein and components for higher yields in the dairy industry. The dataset contained 2,088 females genotyped for beta-casein and kappa-casein. The allelic replacement effect of each marker (β-casein and κ-casein) was estimated using mixed models. The genotype frequencies for beta-casein were 0.01, 0.19 and 0.80 for A1A1, A1A2 and A2A2, respectively. The allele frequency for beta-casein was 0.11 for A1 and 0.89 for the A2 allele. The kappa-casein genotype frequencies were 0.82, 0.17 and 0.01 for AA, AB and BB, respectively. The allele frequency was 0.91 for the A allele and 0.09 for the B allele. There was a significant effect of both genotypes (beta-casein and kappa-casein) on milk production (p < 0.05), with highest estimated mean for animals with beta-casein A2A2 and kappa-casein AA. The estimated effect of allelic replacement by beta-casein with an increase of 202.04 kg of milk for the A2 allele and an increase of 291.09 kg of milk for the A allele of kappa casein. There was no significant effect of beta-casein or kappa-casein genotypes on milk fat and protein production. Therefore, the high frequencies of A2 and A alleles in the Gir Leiteiro breed facilitate selection based on the A2A2 and AA genotypes.