SELECTION INDICES FOR LIMITING DETERIORATION IN REPRODUCTIVE PERFORMANCE ACCOMPANYING SELECTION FOR MILK YIELD TRAITS IN LACTATING COWS

Abstract

This study was conducted with the aim of constructing restricted selection indices to limit the deterioration in the reproductive performance traits accompanied with selection to increase milk yield in Holstein cows in a commercial herd under the Egyptian conditions. The study can be summarized in the following points: Materials and methods - Data of Productive (305-day yields of milk, MY305; fat, FY305 and protein, PY305) and reproductive performance traits (days open, DO; calving interval, CI and number of inseminations per conception, NSC) estimated on 3398 lactation records of 1054 Holstein cows, daughters of 94 bulls and 691 dams were used in this study. - During the period from 1997 to 2011, cows were fed on a Total mixed ration (TMR) according to their needs based on its body weight, milk season and milk production. They were artificially inseminated at 375 kg live weight. Their calves were artificially suckled from birth to weaning at three months of age. - The data were analyzed using a multi-trait animal model with repeated records. The model included the fixed effects of the year-month of calving and parity, as well as the random effects of animal, the permanent environmental effect and the error. Variance and covariance components were estimated using VCE-6 software program package. - Means, coefficient of variabilities, and genetic and phenotypic correlations for productive and reproductive traits were estimated. - Yields of milk (MY305), fat (FY305) and protein (PY305) were included in the aggregate genotype, then the true breeding value