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 o f genetic and phenotypic parameters from two
datasets; results from the Young Horse Evaluation Series (Y H E), 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, how ever, the predicted repeatabilities were
sufficient in magnitude and precision to indicate that the Y HE may prove useful as a
test o f individuals. A much larger and m ore comprehensive dataset was available for
U K eventing horses. Penalty points from each of the three phases - dressage,
show jumping and cross country - and overall com petition w ere converted to normal
scores for analysis. Each phase was separated into 4 different grades of com petition - pre novice, novice, intermediate and advanced. Results show ed heritabilities
significantly different from zero for all phases (0.02-0.23). Correlations between the
grades for each phase w ere 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 o f variance attributed to the rider, permanent
environmental effect and genetics o f the horse w ere estimated separately. These
estimates showed that for m ost grades and phases the m ost important component was
the perm anent 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 (H V s) and
rider values (RVs). Using these values, the intensity o f 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 w ere observed between pre novice and novice (0.018-0.352).
The main aim of this research was to create a model for the prediction of breeding
values for British bred sport horses, an objective that was successfully achieved.
Genetic and phenotypic parameters were estimated for the traits analysed and these
w ere consistent with those contained in the literature. There were a number of novel
aspects to this study, such as the separation of horse and rider in the model, allowing
values to be assigned to each. This led on to another novel aspect o f the research
which was the analysis o f within generation selection of sires, horses and riders
moving through the grades of eventing competition. This study has met its
objectives and also provided a platform for the launch o f further research into sport horse breeding in Britain
