2008م - 1444هـ
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The genetic evaluation o f sport horses is com m on practice on the Continent and in

Ireland but, until now, has not been carried out in Great Britain. The aim o f this

project was to derive m odels for predicting breeding values for British bred sport

horses and hence develop procedures for their evaluation. The research consisted

predom inantly o f the estim ation o f genetic and phenotypic param eters from two

datasets; results from the Young Horse Evaluation Series (YHE), which assesses 4

year old potential sport horses, and com petition data on UK eventing horses. Eleven

traits were m easured in the YHE, including a veterinary score, conform ation, paces

and jum ping ability. A small dataset led to some problem s and m eant that

heritabilities could not be predicted, however, the predicted repeatabilities were

sufficient in m agnitude and precision to indicate that the YHE m ay prove useful as a

test o f individuals. A m uch larger and more com prehensive dataset was available for

UK eventing horses. Penalty points from each o f the three phases - dressage,

show jum ping and cross country - and overall com petition were converted to normal

scores for analysis. Each phase was separated into 4 different grades o f com petition

- pre novice, novice, interm ediate 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 perform ance at advanced level by its perform ance at novice or pre novice

level. For the first tim e, the proportions o f variance attributed to the rider, perm anent

environm ental effect and genetics o f the horse were estim ated separately. These

estim ates showed that for m ost grades and phases the m ost important com ponent was

the perm anent environm ental effect, w ith the rider and genetics becom ing more

im portant as the grades become more challenging. This analysis allowed the

successful prediction o f estim ated breeding values (EBVs), horse values (HVs) 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 o f the phases of

eventing com petition was investigated.