Determination of optimum Holstein inheritance in crossbred dairy cattle based on combined productive and reproductive traits

In dairy cattle breeding, in addition to milk yield, consideration of other productive and reproductive traits is necessary. In order to determine optimum Holstein inheritance in Iranian crossbred dairy cattle, first lactation records of 4917 crossbred dairy cattle collected by Animal Breeding Center between 1991 to 2007 were utilized. Crossbred cows were consisted of different Holstein inheritance including 12.5, 25, 37.5, 50, 62.5, 75 and 87.5 percent. Phenotypic and genetic (co) variance components for milk yield, fat yield, lactation length and age at first calving were estimated by restricted maximum likelihood using single and multiple traits animal models. Then, a selection index was constructed to combine these traits. Optimum Holstein inheritance based on this index was determined by least squares mean comparisons of the index for different Holstein inheritance and simple linear regression. Results indicated that 87.5 percent Holstein inheritance was the optimum level.