Use of test day yields for the genetic evaluation of production traits in Holstein-Friesian cattle

Bayesian methods and Gibbs sampling techniques have been applied to estimat e genetic parameters for test-day (TD) yields in the Spanish Holstein-Fries ian population. Three models were analyzed: (a) multitrait model on success ive TD yields within the first lactation; (b) multitrait model on the first three lactations considering TD yields as repeated measures within lactati ons: (c) random regression model (RRM) on first lactation TD yield. Two alt ernative RRM were adjusted, RRM1 considered random regression on the geneti c effects only, RRM1 included random regressions for the genetic and perman ent environmental effects and allowed for heterogeneous residual variances. In model (a), heritabilities tended to be larger in middle lactation and g enetic correlations among TD measures were large (> 0.80). Large genetic co rrelations among lactations ( > 0.89) and heterogeneous variances for first vs, other lactations were found for model (b). RRM1 was found to be superi or to the simple repeatability model (b) in terms of reducing residual vari ance, However, RRM1 produced very large estimates of the genetic variance a t the beginning and end of the lactation. Genetic and environmental varianc es estimated under RRM2 tended to be close to the multitrait model (a). Lar ge discrepancies in the genetic correlations among daily yields with respec t to the one observed from the multitrait approach were found for RRM1 and, to a lesser extent, for RRM2. (C) 1999 Elsevier Science B.V. All rights re served.