estimation of genetic parameters for production traits in holstein cows of khorasan razavi province

the milk and milk fat production records of 28 holstein herds in khorasan razavi province were analyzed in this study. the records were based on 305 days of milking and were from the first to third milking periods and two times milking per day. the fixed effects of herd-year-season and age of dam at parturition as covariate were fitted in the models of analyses. the (co)variance components were estimated using reml procedure. the heritability values of the first to third lactation period of milk production were 0.27, 0.19 and 0.13; and for milk fat were 0.18, 0.15 and 0.14 respectively. the heritability values under repeatability models for milk production and milk fat were 0.21 and 0.15، respectively. the repeatability value for milk production was 0.46 and for milk fat was 0.35. also، the genetic، phenotypic and environmental correlations between these traits were 0.84، 0.79، and 0.78، respectively.