Associations between milk protein polymorphism and first lactation milk production traits in Finnish Ayrshire cows

Genotypic effects of beta-casein (CN), kappa-CN, and beta-lactoglobulin (LG ) on milk, fat, and protein product;ion and fat and protein percentages wer e estimated for 18,686 Finnish Ayrshire cows in first lactation using an an imal model. Casein genotype effects were estimated including individual bet a-CN and kappa-CN simultaneously in a model and then as composite beta-kapp a-CN. The A(2) allele of beta-CN and the A allele of kappa-CN, as well as t he A(2) allele of beta-CN and the B or E allele of kappa-CN, appeared toget her more frequently than was expected. Because of linkage disequilibrium in the casein loci and, consequently, unbalanced data, some contradictory eff ects of casein genotypes were obtained with the two models. A well-founded way to estimate the effects of casein genotypes was to use beta-kappa-CN ge notypes. Composite casein genotypes including the A(2) allele of beta-CN we re associated with the highest milk and protein production and the lowest f at content, those including the B allele of kappa-CN with the highest prote in content, and those including the E allele of kappa-CN with the lowest pr otein content. The effect of the beta-kappa-CN genotypes on protein content was moderately strong, and the effect was somewhat smaller for other trait s. The AA genotype of beta-LG had a favorable effect on milk and protein pr oduction, and the BE genotype had a favorable effect on fat content.