Genetic Evaluation of Sport Horses in Britain

Abstract

The genetic evaluation of sport horses is common practice on the Continent and in Ireland but, until now, has not been carried out in Great Britain. The aim of this project was to derive models for predicting breeding values for British bred sport horses and hence develop procedures for their evaluation. The research consisted predominantly of the estimation of genetic and phenotypic parameters from two datasets; results from the Young Horse Evaluation Series (YHE), which assesses 4 year old potential sport horses, and competition data on UK eventing horses. Eleven traits were measured in the YHE, including a veterinary score, conformation, paces and jumping ability. A small dataset led to some problems and meant that heritabilities could not be predicted, however, the predicted repeatabilities were sufficient in magnitude and precision to indicate that the YHE may prove useful as a test of individuals. A much larger and more comprehensive dataset was available for UK eventing horses. Penalty points from each of the three phases – dressage, showjumping and cross country – and overall competition were converted to normal scores for analysis. Each phase was separated into 4 different grades of competition – pre novice, novice, intermediate and advanced. Results showed heritabilities significantly different from zero for all phases (0.02–0.23). Correlations between the grades for each phase were high, suggesting that it should be possible to predict a horse’s performance at advanced level by its performance at novice or pre novice level. For the first time, the proportions of variance attributed to the rider, permanent environmental effect and genetics of the horse were estimated separately. These estimates showed that for most grades and phases the most important component was the permanent environmental effect, with the rider and genetics becoming more important as the grades become more challenging. This analysis allowed the successful prediction of estimated breeding values (EBVs), horse values (HVs) and rider values (RVs). Using these values, the intensity of selection on sires, horses and riders progressing from the pre novice to advanced grades in each of the phases of eventing competition was investigated. The highest selection intensities were observed between intermediate and advanced grade (0.634-1.163). The lowest selection intensities were observed between pre novice and novice (0.018-0.352).