Relevance of test information in horse breeding

 

The aims of this study were 1) to determine the role of test results of young

horses in selection for sport performance, 2) to assess the genetic diversity

of a closed horse breed and 3) the consequences of inbreeding for male

reproduction. The study was performed using existing databases containing

records collected on young horses during inspections, which were linked to

databases containing records on sport performance. Multivariate animal

models were applied in estimation of genetic parameters. Heritability

estimates of movement and free-jumping traits collected at Studbook Entry

and at First Stallion Inspection were moderate to high. Free-jumping traits

collected at both inspections showed high to very high positive genetic

correlations to show-jumping in competition. Movement traits collected at

both inspections showed favourably genetic correlations to dressage in

competition.

Subsequently, the effect of limb and foot conformation, in particular the

trait uneven feet, as assessed at Studbook Entry Inspection on performance

and length of sport career have been analysed. Limb and foot conformation

had only weak to moderate genetic correlation to sport performance. Some

foot conformation traits could be identified as risk factors for early

retirement from sports; e.g. occurrence of uneven feet shortened the

competitive life at elite level of jumping.

The development of genetic diversity in a closed breed have been studied

using the pedigree structure of the Friesian horse breed. Considerable loss

of genetic diversity have taken place during the history of the studbook,

corresponding to an average inbreeding rate of 1.3% per generation. Loss of

genetic diversity was mainly due to drift from small effective population size

during several generations. In a subsequent analysis the relation of

inbreeding with semen quality of young Friesian stallions was investigated. It

was concluded that low semen quality in Friesian stallions could not be

attributed to inbreeding. Heritability estimates for semen quality traits were

moderate to high and had substantial variation. Selection can be used to

improve semen quality.

Finally, opportunities for improvement of the breeding program have been

discussed. Selection potentials are calculated to gain insight in the relative

importance of each of the young horse tests to the breeding program.

Additional opportunities to increase selection response have been

discussed.