Records of 152 145 test-day (TD) milk yields, from 7,317 complete first lactations of Holstein cattle raised in Brazil were analysed. Estimate covariance functions for additive genetic and permanent environmental effects, as well as the genetic parameters for TD milk records using random regression models. Variance components were estimated using DFREML. A model including a step function with 17 variances was the most adequate to model the changes in residual variances. The seventh order random regression model for the additive genetic and permanent environmental effects was shown to be the most adequate. However, a sixth order covariance function for the additive genetic effects and a seventh order covariance function for the permanent environmental effect could be sufficient.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 01.49, 2006
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