Summary

Among the species affected by osteochondrosis dissecans, horses are particularly concerned, with around a third of sport horses affected. With the aim of limiting the prevalence of this condition in the Walloon sport horse population, three main areas were investigated in the studies presented in this thesis: the evolution of the prevalence of osteochondrosis dissecans, the evolution window of the lesions and the identification of phenotypic traits correlated with the presence of osteochondral fragments.

These areas were investigated on the basis of data collected since 2006 on more than 1,000 walloon sports foals. The information collected included standardised radiographic examinations, a medical history and an assessment of breeding conditions.

Studies carried out as part of this thesis have shown that the window of appearance and evolution of lesions in the various joints extends beyond the age of 12 months in sport horses. Furthermore, despite the selection of breeding males free of osteochondrosis dissecans in Warmblood studbooks, the prevalence of this disease in the population studied does not appear to have decreased over a period of 19 years. Furthermore, the number of affected individuals was significantly correlated with breeding conditions (feeding and housing) and the presence of sepsis during growth. Finally, certain phenotypic traits, notably a high height at the withers and a large diameter of metacarpal III, were correlated with the presence of lesions, particularly at the tarso-crural and metatarso-phalangeal levels.

The results of these studies suggest that, in order to reduce the prevalence of OCD in the sport horse population, genetic selection based on the exclusion of breeding males with OCD alone would not be sufficient. Furthermore, the observation that the window of evolution of lesions extends beyond one year should be taken into account when carrying out radiographic assessments and choosing treatment, and underlines the importance of maintaining adequate housing and feeding conditions beyond this age. Finally, phenotypic characteristics such as a limited height at the withers could be taken into account in selection strategies.

Link to the full manuscript: https://hdl.handle.net/2268/327926