Estimation of Genetic and Phenotypic Parameters for Productive Life, Milk Yield and Constituents and Milk and Fat Persistency in Holstein Dairy Cows

Genetic and phenotypic parameters were estimated for first parity Holstein cows with records from April 1991 to May 2006 for 305-d milk (Milk305), fat (Fat305), and protein (Pro305) yields, fat (Fat%) and protein (Pro%) percentage, productive life (PL), natural logarithm of somatic cell score (LSCS), lactation length (LL) and milk (Milk3:1), and fat (Fat3:1) persistency. The (co)variance components and genetic parameters were estimated using restricted maximum likelihood (REML) method. Among production traits, the highest heritability (0.26) was for Fat% and the lowest one (0.048) was for Fat3:1 persistency. Heritability estimate for PL was low (0.035). Genetic correlations of PL with production traits were relatively high and positive (except for Fat% and Pro%). PL had the highest genetic correlation with Fat3:1 and Milk3:1 persistency (0.56 and 0.45, respectively). In general, phenotypic correlations between traits were lower than genetic correlations. Milk3:1 and Fat3:1 persistency had favorable genetic correlation with LSCS (-0.34 and -0.36, respectively). It can be suggested to include a combination of production and persistency traits in selection index in order to increase PL and improve udder health.