Volume 3, Issue 6 (3-2013)
Res Anim Prod 2013, 3(6): 46-63 |
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Mohammadi A, Alijani S, Rafat S A, Taghizadeh A, Buhloli M. (2013). Comparison of Fitting Performance of Polynomial Functions in Random Regression Model for Test Day Milk Yield in of Iranian Holstein Dairy Cattle. Res Anim Prod. 3(6), 46-63.
URL: http://rap.sanru.ac.ir/article-1-122-en.html
URL: http://rap.sanru.ac.ir/article-1-122-en.html
1- M.Sc. Student, University of Tabriz
2- University of Tabriz
2- University of Tabriz
Abstract: (7039 Views)
In this research, 701212 test day record for milk yield of first lactation of 199903 Holstein cows from 2006 to 2010 that were collected by Karaj breeding center were used. Random regression model with Legendre polynomials fitting order 2 to 5 of additive genetic effects and permanent environmental effects, Wilmink and Ali-Schaeffer functions were compared under homogeneous residual variance assumption throughout lactation. Genetic parameters were estimated using restricted maximum likelihood (REML). For comparison of models, from -2logL, Akaike’s information criterion (AIC), Bayesian information criterion (BIC), Residual Variance (RV) and Likelihood ratio test (LRT) was used. Based on obtained results, random regression model with Legendre polynomial function (2,5) were chosen as better model. Residual variance decreased as the increase of fitting order for permanent environmental effects in Legendre polynomials. Permanent environmental variance was estimated higher in early lactation than the other lactation stages and additive genetic variance in the early lactation was lower than at the end of lactation. Phenotypic variance of milk yield during lactation was not constant, it was higher at the beginning and the end of lactation. The heritability during lactation did vary among different functions, range from 0.08 to 0.23.
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