The term ‘Developmental Orthopaedic Diseases’ (DOD) encompasses all orthopaedic problems encountered in the growing animal. One of the major pathologies included in this group is osteochondrosis (OC) which is not only a clinical problem for many horses but also affects owners and breeders financially due to the loss of value of the affected animals. The aetiopathogensis of DOD is known to be multifactorial and includes hereditary aspects. Therefore radiological examination of horses is often included in the process of a pre-purchase examination or in stallion selection protocols performed by studbooks. Radiological screening of large groups of animals may however prove difficult and does not necessarily reflect the osteo-articular status of the individual animal. However measurement of blood biomarkers involved in cartilage metabolism could be an interesting alternative to widespread radiographic screening. Veterinarians are often faced with the question: What is the implication of a particular lesion found during radiological screening? The clinical impact of most lesions has been largely described for racing populations but since performance ‘measurements’ are more difficult to obtain in Warmbloods, information on non-racing populations is lacking. Furthermore and independently of the athletic capacities of the animal, any joint pathology that will ultimately lead to degenerative joint disease will hinder the affected individual in daily life. The increased availability and interest in biomarkers reflecting joint disease may reveal the impact of osteochondral fragments discovered during routine radiographic screening on the cartilage of the affected joint. The aims of the present study were multiple. Firstly, we have investigated the prevalence of DOD lesions in a local population prior to the start of athletic activity. A measure of performance in jumping horses was then used in order to investigate the clinical impact of DOD on future performances of affected horses. Biochemical markers (Coll2-1, Coll2-1NO2, myeloperoxidase, IGF-I) known to play a role in cartilage homeostasis and inflammation will be used in order to investigate their ability to predict the overall osteoarticular status of horses. Finally, biochemical markers will be investigated for their capacity to differentiate affected from non-affected animals and for their capacity to reflect the extent of cartilage degradation.
The studied population consisted of a group of horses with a mean age of three years that have not yet been subjected to degenerative processes occurring in joints due to enrollement in an athletic career. This population therefore does not permit any investigation on the aetiopathogenic aspects of DOD lesions as it is known that they occur early in life and remain stable after the age of 24 months. Nevertheless they constitute a perfect population to investigate the impact of DOD on the future career of the animals and on degenerative changes they are able to produce in the joint. The prevalence of DOD in the present population was 38.9%, which is similar to other warmblood populations. A high percentage of horses suffered from effusion of the distal interphalangial joint which may be related to an early and intensive workload put on this joint. This hypothesis that can be supported by the elevated levels of Coll2-1, a marker of cartilage degradation, found in this group of horses. While the different biochemical markers used in this study were not found to predict the overall osteoarticular status of the horses but they provide interesting information individually. IGF-I was shown to be lower in horses with radiological findings compared to unaffected animals. Serum Coll2-1NO2, which is a prognostic marker used in human osteoarthritis, showed a tendency to predict the radiological status of the animals; an increase in Coll2-1NO2 reflected an increased probability that the affected horse would belong to a less favourable osteoarticular status.
Regarding Coll2-1, our work has demonstrated the pertinence of this marker in the horse. Firstly, Coll2-1 was revealed to be elevated in joints affected by an osteochondral fragment which enabled the discovery of a degenerative process inside of the affected joint. This marker was also shown to correlate with macroscopic cartilage degradation measured by arthroscopy. It is therefore understandable that these fragments have the capacity to induce osteoarthritis. These results support the current concept of prophylactic removal of the osteochondral fragments discovered during routine radiographic screenings. As in human medicine, Coll2-1 in the horse can be attributed the term of ‘diagnostical and burden of disease marker’. This means that this marker not only has the potential to differentiate affected from non-affected joints but also can be used to evaluate the severity and extent of the pathology in affected individuals.
Finally, horses affected with osteochondrosis of the stifle were revealed to have poorer jumping performances compared to controls. Conversely, no relation has been found between performance and the presence of DOD in the hock or fetlock. Nevertheless, it should be pointed that a large number of animals involved in the study have probably been operated on after the radiographic screening and before enrolling them in athletic activity. Medical confidentiality and the lack of willingness of owners to discuss the individual surgical status of their animal did not permit the formation of healthy, operated and non-operated groups. The absence of any effect of fetlock or hock DOD on performance may therefore be the result of surgery, as the inciting cause of osteoarthritis and lameness has been removed.
In conclusion, considering the hereditary components of the investigated pathologies, the impact some have on the athletic career of the affected individuals and their capacity to induce joint degeneration, it seems logical to continue selection of healthy animals for reproduction in order to decrease prevalence of the disease. As the aetiology is known to be multifactorial it is certainly as important to continue research into methods that may limit the appearance or severity of the disorder.