Effects of composite casein and β-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 genotypes on the renneting properties and composition of milk were estimated for 174 and 155 milk samples of 59 Finnish Ayrshire and 55 Finnish Friesian cows, respectively. As well as the random additive genetic and permanent environmental effects of a cow, the model included the fixed effects for parity, lactation stage, season, kappa-beta-casein genotypes and beta-lactoglobulin genotypes. Favourable renneting properties 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 firmness 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 allele on renneting properties was unfavourable compared with that of the kappa-casein B allele, and possibly with that of the A allele. The beta-lactoglobulin genotypes had no effect on renneting properties but they had a clear effect on the protein composition of milk. The beta-lactoglobulin AA genotype was associated with a high whey protein % and beta-lactoglobulin concentration and the BB genotype with a high casein % and casein number.