the effect of milking frequency on milk and fat yield, and their curves in holstein dairy cows of iran

milk and fat yields in 3x and 4x milking schedule in holstein cows of iran were investigatedusing 374170 milk and fat yield test day records measured on the 1st and 2nd lactions of 54580 dairycattle coming from 205 herds. the records had been collected from 2007 to 2009 by the iraniananimal breeding center (iabc). the results indicated that an increases in the milking frequency from3x to 4x increases milk and fat yields during the lactation periods by 14 and 12.6%, respectively.these values amounted to 15.6 % and 17 % during the lactation peaks. estimated of co (variance)components were derived from a random regression model using asreml. heterogeneous structurewas used for the residual variance. a value of 0.25 was estimated for the heritability of milk yield in3x and 4x milking schedules. the heritability of fat yield in the 3x and 4x milking times wererecorded as 0.11 and 0.17, respectively.