Genetic (co)variance components across age for Show Jumping performance as an estimation of phenotypic plasticity ability in Spanish horses.

The purpose of this study was to study phenotypic plasticity ability for Show Jumping performance in horses according to age differences. For this study, 11 352 participations, belonging to 1085 horses grouped by age (4-, 5- or 6-year olds), were analysed. repeatability animal models (RAM) and multiple trait animal models (MTAM) were compared. RAM assumed the same covariance components for all age groups, whereas MTAM considered the results of every animal at every age group as different (but correlated) traits. The age, sex, starting order and training level were included as fixed effects. The random effects were the animal, the individual permanent environment, the competition and the rider. Six models were compared, and the rider-horse interaction was added as a random effect; furthermore, heterogeneous residual variance was taken into consideration only for MTAM. The study of the genetic correlations between age groups highlighted the presence of an age-genotype interaction and, therefore, an underlying environmental effect. This study may allow us to select horses with a plastic response, which show either a gradual response or a precocious response and thus gain or lose genetic potential with age, respectively.