Estimation of Genetic Trends for Test-Day Milk Yield by the Logarithmic Form of Wood Function Using a Random Regression Model
محورهای موضوعی : Camelز. پزشکیان 1 , ع.ا. شادپرور 2 , س. جوزی شکالگورابی 3
1 - Department of Animal Science, Faculty of Agricultural Science, University of Guilan, Rasht, Iran
2 - Department of Animal Science, Faculty of Agricultural Science, University of Guilan, Rasht, Iran
3 - Department of Animal Science, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran
کلید واژه: milk yield, Holstein, wood function, genetic trend, random regression model,
چکیده مقاله :
Estimation of genetic trends is necessary to monitor and evaluate selection programs. The objective of this study was to estimate the genetic trends for milk yield in Iranian Holsteins cows using random regression test day model. Data set was consisted of 743205 test-day records from 1991 to 2008, which were collected by the Animal Breeding Centre of Iran. Breeding, environmental and phenotypic values were estimated using a random regression test-day model. The logarithmic form of Wood function was chosen to fit the additive genetic and permanent environmental effects of milk yield. Genetic, environmental, phenotypic trends were estimated by regressing the mean of breeding values, environmental values and phenotypic values on birth year. The genetic and phenotypic trends were positive and significant, whereas environmental trends were not significant. Genetic trends of sires and dams were estimated separately and it was positive and significant for dams, but it was not significant for sires. The phenotypic, environmental and genetic correlation between each days in milk and total 305 days were estimated. The correlations related to breeding values were weak and it showed that with the logarithmic transformation of milk yield, persistency can be improved independently from milk production.
برآورد روند ژنتیکی جهت نظارت و ارزیابی برنامههای انتخاب ضروری است. موضوع این مطالعه برآورد روند ژنتیکی تولید شیر گاوهای هلشتاین ایران با استفاده از مدل تابعیت تصادفی بود. دادهها شامل 743205 رکورد روزآزمون از سال 1991 تا 2008 بود که توسط مرکز اصلاح نژاد دام ایران جمعآوری شده بود. ارزشهای اصلاحی، محیطی و فنوتیپی با استفاده از یک مدل تابعیت تصادفی برآورد شد. شکل لگاریتمی تابع وود جهت برازش اثرات ژنتیکی افزایشی و محیطی دائمی تولید شیر انتخاب شد. روندهای ژنتیکی، محیطی و فنوتیپی به وسیله تابعیت میانگین ارزشهای اصلاحی، محیطی و فنوتیپی به سال تولد محاسبه شد. روندهای ژنتیکی و فنوتیپی مثبت و معنیدار بود، در حالیکه روند محیطی معنیداری برای تولید شیر مشاهده نشد. روند ژنتیکی تولید شیر برای نرها و برای مادهها به صورت جداگانه محاسبه شد که این روند برای مادهها مثبت و معنیدار بود اما برای نرها معنیدار نبود. همبستگیهای فنوتیپی، محیطی و ژنتیکی بین هر روز شیردهی و تولید کل 305 روز نیز برآورد شد. همبستگیهای مربوط به ارزشهای اصلاحی ضعیف گزارش شد که این بدین معنی است که با تغییر شکل لگاریتمی تولید شیر، میتوان تداوم شیردهی را به طور مستقل از تولید شیر بهبود بخشید.
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