EFFECTS OF COMPOSITE CASEIN AND BETA-LACTOGLOBULIN GENOTYPES ON RENNETING PROPERTIES AND COMPOSITION OF BOVINE-MILK BY ASSUMING AN ANIMAL-MODEL

The effects of kappa-beta-casein genotypes and beta-lactoglobulin geno types on the renneting properties and composition of milk were estimat ed for 174 and 155 milk samples of 59 Finnish Ayrshire and 55 Finnish Friesian cows, respectively. As well as the random additive genetic an d permanent environmental effects of a cow, the model included the fix ed effects for parity, lactation stage, season, kappa-beta-casein geno types and beta-lactoglobulin genotypes. Favourable renneting propertie s were associated with kappa-beta-casein genotypes ABA(1)A(2), ABA(1)A (1) and AAA(1)A(2) in the Finnish Ayrshire, and with ABA(2)B, AAA(1)A( 3), AAA(2)A(3), ABA(1)A(2) and ABA(2)A(2) in the Finnish Friesian. The favourable effect of these genotypes on curd firming time and on firm ness of the curd was partly due to their association with a high kappa -casein concentration in the milk. The effect of the kappa-casein E al lele on renneting properties was unfavourable compared with that of th e kappa-casein B allele, and possibly with that of the A allele. The b eta-lactoglobulin genotypes had no effect on renneting properties but they had a clear effect on the protein composition of milk. The beta-l actoglobulin AA genotype was associated with a high whey protein % and beta-lactoglobulin concentration and the BB genotype with a high case in % and casein number.