Genetic parameters of milk protein composition and coagulation properties in simmental cattle

ignificant associations between milk protein fractions and milk coagulation properties (MCP) have been reported (Wedholm et al., 2006), but genetic correlations between milk proteins contents and MCP traits have never been investigated. The aim of this study was to estimate genetic parameters for protein composition and MCP in Simmental cattle. Data. Contents of αS1-CN, αS2-CN, β-CN, γ-CN, κ-CN, β-LG, and α-LA and genotypes of cows at CSN2, CSN3, and BLG loci were assessed by reversed-phase HPLC in 2,167 milk samples of Simmental cows, using the method proposed by Bonfatti et al. (2008). Measures of rennet clotting time (RCT) and curd firmness (a30) were obtained by using the Computerized Renneting Meter (CRM-48, Polo Trade, Monselice, Italy). Non-coagulating milk was not considered in the statistical analysis. Conclusion Selection for the total casein content of milk would not be useful for the genetic improvement of milk coagulation properties. Selection for increasing the β-CN and κ-CN contents or decreasing the content of αS1-CN of milk seems to be a more attractive alternative for improving renneting ability, also considering their high heritability. Heritability of MCP was still appreciable after adjustment for casein haplotypes and BLG genotypes, suggesting that the recording of this trait can not be replaced by genotyping of animals for milk protein variants. However in light of a direct effect of CSN2 B variant on MCP, CSN2 locus could be used to implement marker-assisted selection schemes for the genetic improvement of MCP.