Individual milk samples from 121 cows in mid lactation of the Swedish Red and Swedish Holstein breeds with known protein genotypes of b-and k-casein and b-lactoglobulin were analysed. Chromatographically pure chymosin was added to skim milk and rheological properties of the gels were measured using a Bohlin VOR Rheometer. Coagulation time (CT) and curd firmness after 25 min (G 0 25 ) were registered for each sample. The B allele of k-casein was associated with improved coagulating properties of milk, whereas the E allele showed a negative effect on these traits. The b-casein A 2 A 2 genotype was associated with inferior milk coagulation characteristics. Total protein concentration of milk was positively associated with curd firmness, but showed no association with milk coagulation time. r

Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is a key enzyme in triacylglycerol synthesis in the mammary gland, and the corresponding gene has emerged as a strong candidate for the variation in milk fat percentage. In this study, the allele frequencies and effects of the DGAT1 K232A variants in the Swedish dairy breeds Swedish Red and Swedish Holstein were investigated. A total of 239 cows, 143 of the Swedish Red breed and 96 of the Swedish Holstein breed, in the experimental herd at the Swedish University of Agricultural Sciences were genotyped for the DGAT1 polymorphism. The Swedish Red cows in the herd belonged to 1 of 2 selection lines with high or low milk fat percentage, respectively, but with similar high total milk energy production. The frequency of the K variant was found to be significantly greater in the high-fat line than in the low-fat line. The average frequency of the K variant in the 2 lines of the Swedish Red cows was 0.09 compared with 0.12 among the Swedish Holstein cows. Mixed model analysis was used to estimate the effect of the DGAT1 K232A polymorphism based on 16,866 test-day records for milk production traits. In accordance with previous studies, the most pronounced effects were found for fat and protein percentages and milk yield; and the K variant was associated with an increase in milk fat and protein percentages but less milk yield compared with the A variant. Less pronounced effects were found for yields of fat and protein for which the K variant was associated with greater fat yield but less protein yield.