an estimation of genetic parameters and trends for milk and fat yields and fat percentage for holstein dairy cattle in khorasan province using univariate and repeatability animal models

genetic parameters and trends for milk and fat yields as well as for fat percentage were estimated from 35,438 milk production records (305d, 2x) of 17,971 holstein dairy cattle in 133 herds during the period of 1990-2003 in khorasan province. variance components were estimated using restricted maximum likelihood statistical method applying univariate and repeatability animal models. for the univariate animal model, the heritability estimates for milk, fat yield, and fat percentage were 0.28, 0.23 and 0.26 respectively while for the repeatability animal model the heritability estimates were respectively 0.23, 0.19 and 0.26. for the traits, repeatability estimates were 0.46, 0.36 and 0.42 respectively. based upon predicted breeding values, the estimated annual genetic trends estimated for sires were 14.33 kg, -0.11 kg and -0.061 % for milk fat yield, and fat percentage respectively while, the corresponding respective figures for daughters were 11.06 kg, -0.076 kg and -0.005 %.