genetic evaluation of productive and reproductive traits of holstein dairy cows in the north of iran

in the present study, to estimate genetic parameters and genetic and phenotypic trends in holstein dairy cows in the north of iran, the records from first lactation of 11398 collected from 1989 to 2006 were used. records were collected from 290 herds. productive traits were 305 day-2x adjusted milk and fat yield and reproductive traits were age at first calving, calving interval and dry days. genetic parameters were estimated by univariate and bivariate animal model using asreml software. estimated heritabilities for 305 day-2x milk, fat, age at first calving, calving interval and dry days gathered from univariate analysis were 0.27 (±0.02), 0.19 (±0.02), 0.1 (± 0.02), 0.03 (±0.01) and 0.1 (±0.02) respectively. genetic correlation between milk and fat yield was 0.82. genetic correlations of milk and fat production with age at first calving were -0.2 and -0.23 and with calving interval were 0.31 and 0.40, respectively. genetic trends for milk and fat yield were 2.8 (±0.4) and 0.05 (±0.01) kg/year and for age at calving, calving interval and dry days were -0.28 (±0.01), 0.02 (±0.002) and -0.03 (±0.004) days/year, respectively. phenotypic trends for these traits were 113.24 (kg/year), 2.3 (kg/year), -2.66 (days/year), 0.37 (days/year) and -0.36 (days/year). based on unfavorable genetic correlations between productive and reproductive traits, using a selection index including both of these traits is necessary for holstein dairy cows.