Genetic parameters for αS1-casein and αS2-casein phosphorylation isoforms in Dutch Holstein Friesian

Relative concentrations of αS1-casein and αS2-casein (αS1-CN and αS2-CN) phosphorylation isoforms vary considerably among milk of individual cows. We estimated heritabilities for αS2-CN phosphorylation isoforms, determined by capillary zone electrophoresis from 1,857 morning milk samples, and genetic correlations among αS2-CN phosphorylation isoforms in Dutch Holstein Friesian. To investigate if phosphorylation of αS1-CN and αS2-CN are due to the same genetic mechanism, we also estimated genetic correlations between αS1-CN and αS2-CN phosphorylation isoforms as well as the genetic correlations between the phosphorylation degrees (PD) of αS1-CN and αS2-CN defined as the proportion of isoforms with higher degrees of phosphorylation in total αS1-CN and αS2-CN, respectively. The intra-herd heritabilities for the relative concentrations of αS2-CN phosphorylation isoforms were high and ranged from 0.54 for αS2-CN-10P to 0.89 for αS2-CN-12P. Furthermore, the high intra-herd heritabilities of αS1-CN PD and αS2-CN PD imply a strong genetic control of the phosphorylation process, which is independent of casein production. The genetic correlations between αS2-CN phosphorylation isoforms are positive and moderate to high (0.33-0.90). Furthermore, the strong positive genetic correlation (0.94) between αS1-CN PD and αS2-CN PD suggests that the phosphorylation processes of αS1-CN and αS2-CN are related. This study shows the possibility of breeding for specific αS1-CN and αS2-CN phosphorylation isoforms, and relations between the phosphorylation degrees of αS1-CN and αS2-CN and technological properties of milk need to be further investigated to identify potential benefits for the dairy industry.