Estimation of Genetic Parameters and Variance Components of Milk Traits in Holstein-Friesian and British-Holstein Dairy Cows

Summary The objectives of this study were to estimate the genetic parameters of milk traits of dairy cows and to examine the associations among these traits in both Holstein-Friesian and British-Holstein. The data used in this study was obtained from (LSUK), an organisation for the recording of milk, health and service parameters of dairy cows in Scotland. The data consisted of information on total lactation milk, fat and protein yield. The final number of production records retained in the production database after all edits was 70931. Variance components and genetic parameters for milk, fat and protein yield were estimated using the ASREML program. Analysis for milk, fat and protein yield was conducted for each of the prepared data sets using a univariate animal model. Mean calving age ranged from 29-65 months. The mean lactation length ranged from 300-320 days. The heritabilities of these traits were ranging from 0.22 to 0.52. The heritabilities of milk, fat and protein yield were higher in Holstein-Friesian than British-Holstein. For most of the traits, phenotypic correlations were larger than the genetic correlations. The results showed that there were moderate-strong positive genetic and phenotypic correlations among the production traits. The genetic correlations ranged from 0.38 between milk and fat yield to 0.92 between milk and protein yield.