Brazilian Sport Horse: genetic parameters for approval of Brasileiro de Hipismo stallions

摘要

The aim of this study was to evaluate genetic parameters for subjective scores given at the Brazilian Sport Horse (BSH) Stallion Approval by estimating heritability (h(2)) for morphological, gait, and jumping traits and genetic correlations (gamma(g)) among the functional ones and by verifying selection feasibility. The analysis included 1179 complete evaluations from 294 horses, by 4.26 +/- 0.96 judges. Each trait was evaluated using mixed models in SAS (R) v9.2, considering the individual as a random effect. Variance components and genetic parameters were obtained by single and two-trait animal models in a derivative-free restricted maximum likelihood analysis. Since many jumping traits were not described in Breed Regulation, mixed model results were used to enlighten the criteria adopted in the assignment of scores. Balanced bodies and conformations that favor collection were preferred by judges and presented moderate heritabilities. Additive variation was found for most jumping traits, with heritability equal to 0.74 (se = 0.04) for overall jump, and estimates for the separate aspects of the jump movement ranging from near null to 0.43 (se = 0.07) for temperament. Morphological scores had little effect over gait and jump scores while trot may be indicative of some additive value for jump distance and canter for hind limb mechanics. Conformation evaluations of separate body regions presented heritability estimates similar to previous studies and may provide more informative breeding values.