ociations Between Casein Haplotypes and First Lactation Mil Production Traits in Finnish Ayrshire Cows

摘要

The objective of this study was to estimate the effects of fi-K-casein (CN) haplotypes on first-lactation milk production traits. The fiK-CN haplotypes were deduced using information on [β- and K-CN genotypes of cows and their sires for 16,973 Finnish Ayrshire cows that had at least nine paternal half sibs. Effects of CN haplo- types on milk production traits were estimated for one haplotype at a time using an animal model, which in- cluded the fixed effects for calving year and month, age at calving, days open, β-lactoglobulin, and a βdK-CN haplotype. Differences in milk production traits were also estimated between haplotype combinations A_lA+A_2B and A_1B+A_2A within beta-K-CN genotype A_lA+A_2B and between combinations A_1E+A_2A and A_lA+A_2E within genotype A_1A_2AE. The β-K-CN haplo- types A_2A and A_2B were associated with high milk and protein yields and low fat content, and those that in- cluded the beta-CN A1 allele were associated with low yields and high fat content. Protein content was affected by the K-CN locus; haplotype A_1B was associated with high protein content and A_1E was with low protein content. The haplotype combination A_1A+A_2B was asso- ciated with 140 kg more milk yield (P = 0.045) and 0.03 percentage units less protein content (P = 0.055) than combination A_1B+A_2A, and combination A_1A+A_2E showed 0.02 percentage units greater protein content (P = 0.098) than A_1E+A_2A. These results indicate that genes linked to the CN loci contribute to the variation in milk yield and protein content.