Many dairy cattle organisations consider to introduce a test-day model for breeding value estimation for milk production traits. Several authors have used random regression models to estimate genetic parameters, which have the advantage that the covariance matrices are estimated directly from the data. However, some authors have reported increasing variances at the beginning and end of the lactation trajectory, which were not consistent with multi-trait results (van der Werf et al. 1998; Jamrozik and Schaeffer 1997; Pool 2000; Kettunen et al. 2000). To reduce this effect, Gengler and Wiggans (2001) have suggested to add a random effect of herd x lactation stage to the model. The aim of this study was to analyse the effect of herd specific random regression curves on the estimated genetic parameters in a test-day model for protein yield

A. PW de Roos, A. GF Harbers, Gerben de Jong

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.05, 2002
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