مطالعه اثر تغییر اندازه گله، نوع اسپرم، هم پوشانی نسل ها و اهداف اصلاحی بر پیشرفت ژنتیکی گاوهای شیری هلشتاین با استفاده از شبیه سازی تصادفی

The effects of herd size, semen type, generation overlapping and breeding goal on genetic gain in Holstein cows were studied through stochastic simulation. Three levels of herd size (100, 200, and 400), two levels of semen type (unsexed and sexed), three levels of generation overlapping (low, average and high) and two levels of breeding goal (narrow and broad) were combined together to make 36 scenarios. A base population of 5000 cows recorded for 6 traits (milk, fat and protein production, age at first calving, calving interval and somatic cell score) were simulated for 30 years. Each year 50 young bulls, 10 active sires and 200 bull dams were selected from the population based on economical selection index. The genetic gain changes, inbreeding rate and generation interval were examined for all scenarios. The results showed that genetic gain for broad breeding goal, unsexed semen, herd size 400 and low generation overlapping were higher by 0.6, 3.6, 0.4, 0.5 percent compared with narrow breeding goal, sexed semen, herd size 100 and high generation overlapping, respectively. Inbreeding changes for broad breeding goal, unsexed semen, herd size 100 and average generation overlapping were more than the other levels of these factors. Estimated breeding value for cow dams (CD) were 34.3 % higher when sexed semen was used compared with the unsexed semen. These results were suggested that broad breeding goal, large herd size, sexed semen and high generation overlapping should be noticed in Holstein selection programs.