Estimation of Variance Components for Milk Production Traits in Iranian Holstein Cows

In this research, estimation of genetic parameters for milk production trait was performed by using collected data from 1991 to 2010 in Iranian Holstein dairy cattle. Genetic parameters were estimated by MATVEC Microsoft, using animal model, with univariate and multivariate analysis. The data set were including 161328, 123369 and 81013 records for first, second and third lactations, respectively. Based on univariate analysis, heritability estimates for three lactations were 0.25, 0.20 and 0.15, respectively. Multivariate analysis was performed twice for each lactation and variances and heritability estimates were averaged. Heritability estimates of milk yield were 0.25, 0.21 and 0.15 in first, second and third lactation, respectively, with multivariate analysis. Genetic correlation were 0.95, 0.98 and 0.91 between first-second, second-third and first-third lactations and phenotypic correlations between them were 0.65, 0.62 and 0.55, respectively. Results showed that the heritability estimates of milk yield were decreased from the first to the third lactation; also, genetic and phenotypic correlations between consecutive lactations (first-second and second-third) were more than inconsecutive lactations (first-third) lactations.