genetic and phenotypic parameters for milk production traits in the first and second lactation in romanian simmental dairy cows

the aim of the present study was to estimate genetic and phenotypic parameters of milk production traits in the first and second lactations of romanian simmental dairy cattle. for the estimation of variance, heritability, genetic and phenotypic correlations among milk yield, fat yield, protein yield, and percentages of fat and protein, 3400 first and second lactation records over a period of five years (2005-2010) were evaluated. genetic correlations of the yields of milk, fat, protein, and percentages of fat and protein in the first lactation were situated among the lowest value of -0.28 between milk yield and protein percentage and the highest value of 0.31 between milk and milk protein yield. phenotypic correlations were situated from the lowest value of -0.02 registered among yields of milk, fat and protein and protein percentage, and the highest value of 0.98 for milk yield and fat percentage. accordingly, if the selection goal is defined as maximizing the useful yield while maintaining fat and protein content, the selection criterion must include fat yield, protein yield, and protein content.