Two-step versus joint analysis of Von Bertalanffy function

Two procedures of analysis of growth data have been compared under the assu mption of the Von Bertalanffy function. The first was based on a two-step p rocedure: initially, estimates of individual growth curve parameters are ob tained, and, then a mixed model is applied to obtain (co)variance component s and breeding values. The second procedure makes use of a joint analysis, obtaining simultaneously growth curve parameters (co)variance components an d breeding values. Within the scope of a simulation scheme, the joint proce dure showed a clear advantage in estimation of (co)variance components and prediction of breeding values, whereas the two-step method showed biased re sults in heritabilities and residual correlations.