کاربرد تابع نمایی ویلمینک در تحلیل ژنتیکی صفات شیر اوج شیردهی و زمان اوج شیردهی گاوهای هلشتاین خراسان رضوی

Background: estimation of genetic parameters is of central importance as an animal breeding is planed and monitored. objectives: this study aimed to genetically analysis of peak milk yield (pmy) and peak time (pt) traits. methods: a total of 130,668 test day milk records belonging to 15,183 first parity holstein cows from 131 dairy herds of razavi khorasan during calving year 2000-2009 were used. for computing pmy and pt, estimated parameters of wilmink's exponential function were applied. the function parameters were estimated using sas software. additive genetic, environmental variance components as well as heritability of the traits were estimated through a single trait animal model using dmu program. genetic trend was estimated based upon a weighted linear regression of average predicted breeding value on calving year. results: heritability of pmy and pt were found to be 0.17±0.018 and 0.051±0.011, respectively. a negative annual and significant (p < 0.05) genetic trend (-0.014 kg) was revealed for pmy. for pt, genetic trend was 0.006 day per year and not statistically significant. conclusions: with respect to the heritability of py trait it could be utilized in genetic selection of the cows in razavi khorasan dairy herds.