The aim of this study was to compare and evaluate the use of on-test age (ONA), off-test age (OFA), on-test weight (ONW), and off-test weight (OFW) as covariates for analysing average daily gain (ADG) in Landrace (LD), Large White (LW) and Pietrain (PT) swine breeds. One- and two-traits analyses were carried out using Restrict Maximum Likelihood method, with a statistical model that included the fixed effect of contemporary group, the random genetic effects of animal and maternal (the latter just for LD breed), and the random effect of litter. Genetic correlations between ONW and ADG and, OFW and ADG were, respectively, 0.46 and 0.96 for LD, 0.40 and 0.96 for LW, and 0.51 and 0.97 for PT. The heritability estimates for ADG were similar for the three breeds and around 0.28 and 0.10, respectively, when ONA and OFW were included as covariates in the model. The use of ONA or OFA would permit the comparison of animals ADG at the same physiologic age, without affecting genetic analyses. Using ONW or OFW (mainly the latter) would cause large decrease on genetic variability of ADG in the populations studied.
off-test age; off-test weight; on-test age; on-test weight
