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Genetic parameters for Friesian cows were estimated from 9155 lactation records for 3635 cows sired by 184 bulls covered 34 years (1982-2015) in two herds Sakha and El-Karada , belonging to the Animal Production Research Institute, Ministry of Agriculture and Land Reclamation, Egypt. Multi-trait repeated animal models were employed using the REML procedure to estimate covariance components of total milk yield (TMY), service period (SP) and calving interval (CI). There is sufficient genetic variation (indicated by the coefficient of genetic variation) in total milk yield, service period and calving interval traits (15.6, 3.6 and 3.7%, respectively). Estimates of heritability for TMY, SP and CI traits were 0.170, 0.010 and 0.044, respectively. Permanent environmental variance ratios were 0.162, 0.017 and 0.048 for TMY, SP, and CI, respectively. Genetic correlations among SP and CI traits were high (0.998), however genetic correlations of reproductive with productive traits were unfavorable (0.512-0.661). The results indicated the possibility of continued selection for increased milk production which has deleterious effects on reproductive traits. The annual genetic changes were positive for TMY, SP, and CI (7.76 kg/yr, 0.076, and 0.24 d/yr, respectively). These positive trends indicate that there has been success in choosing better sires.The corresponding annual phenotypic changes for the same traits were positive (13.9 kg/yr, 0.029 and 0.82 d/yr, respectively). Positive annual genetic and phenotypic changes for SP and CI indicated that with improving milk yield the SP and CI will be increased. The financial situation of the farm is affected by the extension of the calving interval. The lower the calving interval, the more profitable the farm becomes, and prolonging this period for one day causes a financial loss for the farm.

journal of animal and poultry production

Genetic and Phenotypic Parameters and Trends for Milk Yield, Service Period and Calving Interval and The Economic Impact of Extending A Calving Interval on-Farm Profitability in Friesian Cows in Egypt