Associations between casein haplotypes and milk production traits of Swiss Brown cattle.

Effects of casein haplotypes and beta-lactoglobulin (LG) genotypes on milk protein fractions and on daughter yield deviations for milk performance traits were estimated from a daughter design. Offspring of seven Swiss Brown sires with the haplotypes B-A-B-A and B-A-B-B for alpha s1-, alpha s2-, beta-, and kappa-caseins were selected. The milk of daughter groups with paternal haplotype B-A-B-A was associated with lower casein content and higher whey protein content compared with B-A-B-B. Because of these contrary effects, the true protein content was not affected by the paternal haplotypes. The effects of maternal haplotypes were significant on true protein and casein content but not on whey protein content. The beta-LG genotypes had highly significant effects on casein and whey protein content. The effect of beta-LG BB was positive on casein and negative on whey protein content compared with beta-LG AA; the effect of beta-LG AB was intermediate. No significant effects of paternal haplotypes were found for daughter yield deviation on kilograms of milk, fat, and protein or percentages of fat and protein. The effects of the beta-LG genotypes were, independent of the parental haplotypes, close to significant on daughter yield deviation for percentage of protein. The beta-LG BB tended to be associated with a higher protein content compared with beta-LG AA. The effects for beta-LG genotypes showed additive gene effects. The analysis of paternal haplotypes within sires revealed a contrary effect of haplotypes for two of the seven sires for casein content. The paternal haplotypes within sire showed, although not significant, that haplotypes of the two sires had a contrary effect on daughter yield deviation for percentage of protein as well.