CASEIN HAPLOTYPES AND THEIR ASSOCIATION WITH MILK-PRODUCTION TRAITS IN THE FINNISH AYRSHIRE CATTLE

Polymorphism of casein genes was studied in half-sib families of artif icial insemination bulls of the Finnish Ayrshire dairy breed. Ten gran dsires and 300 of their sons were genotyped for the following polymorp hisms: alpha(s1)-casein (B, C), beta-casein (A(1), A(2)), the microsat ellite within the kappa-casein gene (ms(5), ms(4)) and kappa-casein (A , B, E). Nine different combinations of these alleles, casein haplotyp es, were found. Associations between casein haplotypes and milk produc tion traits (milk and protein yield, fat and protein percentage and mi lking speed) were studied with ordinary least-squares analysis to find a direct effect of the haplotypes or an association within individual grandsire families using the granddaughter design. Estimated breeding values of sons were obtained from cow evaluation by animal model. No direct effect of the casein haplotypes on the traits was found. Within grandsire families, in one out of four families the chromosomal segme nt characterized by haplotype 3 (B-A(2)-ms(4)-A) was associated with a n increase in milk yield (P<0.01) and a decrease in fat percentage (P< 0.01) when contrasted with haplotype 8 (B-A(1)-ms(4)-E). The results p rovide evidence that in the Finnish Ayrshire breed at least one quanti tative trait locus affecting the genetic variation in yields traits is segregating linked to either haplotype 3 (B-A(2)-ms(4)-A) or 8 (B-A(1 )-ms(4)-E).