Associations between casein haplotypes and first lactation milk productiontraits in Finnish Ayrshire cows

The objective of this study was to estimate the effects of beta-kappa -case in (CN) haplotypes on first-lactation milk production traits. The beta-kapp a -CN haplotypes were deduced using information on beta- and kappa -CN geno types of cows and their sires for 16,973 Finnish Ayrshire cows that had at least nine paternal half sibs. Effects of CN haplotypes on milk production traits were estimated for one haplotype at a time using an animal model, wh ich included the fixed effects for calving year and month, age at calving, days open, beta -lactoglobulin, and a beta-kappa -CN haplotype. Differences in milk production traits were also estimated between haplotype combinatio ns A(1)A+A(2)B and A(1)B+A(2)A within beta-kappa -CN genotype A(1)A(2)AB an d between combinations A(1)E+A(2)A and A(1)A+A(2)E within genotype A(1)A(2) AE. The beta-kappa -CN haplotypes A(2)A and A(2)B were associated with high milk and protein yields and low fat content, and those that included the b eta -CN A(1) allele were associated with low yields and high fat content. P rotein content was affected by the kappa -CN locus; haplotype A(1)B was ass ociated with high protein content and A(1)E was with low protein content. T he haplotype combination A1A+A2B was associated with 140 kg more milk yield (P = 0.045) and 0.03 percentage units less protein content (P = 0.055) tha n combination A(1)B+A(2)A, and combination A(1)A+A(2)E showed 0.02 percenta ge units greater protein content (P = 0.098) than A(1)E+A(2)A These results indicate that genes linked to the CN loci contribute to the variation in m ilk yield and protein content.