Estimation of genetic and phenotypic parameters for productive life, milk yield and constituents and milk and fat persistency in Iranian Holstein cows

Arash Chegini, Fahimeh Khorami-Zadeh


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, environmental 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.

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