Abstract

Records on 7574 first lactation cows were used to investigate the associations between milk protein genetic variants and 305-day milk, fat, and protein yields. Friesians, Jerseys and Ayrshires and their crosses were represented in the data. Milk samples were typed for 3 casein (CN) proteins as1-CN (B,C), b-CN (A1, A2), k-CN (A,B) and 1 whey protein b- lactoglobulin (LG) (A,B). The model used to describe the data included the additive genetic effect of animal and the four protein phenotypes. The interaction between breed and as1-CN phenotype and between breed and b-CN phenotype was significant (P<0.05) for milk, fat and protein yields while the interaction between breed and k-CN phenotype was significant (P<0.05) only for protein yield. The interactions associated with the as1-CN and k-CN phenotypes were scale effects while the interactions associated with b-CN resulted from reranking of protein phenotype across the breeds. Friesian and Jersey as1-CN BB cows had higher (2.8% and 0.8%, respectively) milk production and lower (0.3% and 1.2%, respectively) protein production than BC animals while the differences between the phenotypes for fat production were small. The b-CN A2 allele was associated with increased production in the Friesians with A2A2 cows producing approximately 2% more milk, fat and protein than A1A1 cows. The opposite effect was found in Jerseys where A2A2 cows produced 3-4% less milk, fat, and protein than A1A1 cows. The B allele of k-CN was associated with a 0.6 to 3.5% increase in production. The b-LG BB phenotypes produced approximately 1.3% less milk and protein and 1.2% more fat than the AA phenotypes. The dominance effect was not significant (P<0.05) for any of the protein phenotypes.

AM, Winkelman, and BW Wickham

Proceedings of the New Zealand Society of Animal Production, Volume 56, , 24-27, 1996