Early exercise advances the maturation of glycosaminoglycans and collagen in the extracellular matrix of articular cartilage in the horse

Summary Reasons for performing study: Training at a very young age may influence the characteristics of the collagen network of articular cartilage extracellular matrix (ECM) in horses. Objectives: To investigate whether increasing workload of foals results in significant changes in the biochemical composition of articular cartilage ECM. Methods: Thoroughbred foals (n = 33) were divided into 2 different exercise groups from age 10 days‐18 months. One group (PASTEX; n = 15) was reared at pasture; the other (CONDEX; n = 18) underwent a specific additional training programme that increased workload by 30%. At mean age 18 months, 6 animals from each group were subjected to euthanasia. The proximal articular surface of the proximal phalanx of the right hindlimb was examined for the presence of damage using the cartilage degeneration index (CDI). Samples were taken from 2 sites with known different loading patterns. Slices were analysed for DNA, glycosaminoglycans (GAG), collagen and post translational modifications of collagen (formation of hydroxylysylpyridinoline [HP] and pentosidine crosslinks, and hydroxylysine [Hyl]), and exercise groups and different sites compared. Results: There were no differences in CDI between PASTEX and CONDEX animals, indicating the absence of extra joint damage due to the exercise regimen. There were site‐related differences for most biochemical variables, corroborating earlier reports. All biochemical variables showed differences between PASTEX and CONDEX groups at one of the sites, and some at both. GAG and collagen levels were lower in the CONDEX group whereas Hyl, HP crosslinks and pentosidine crosslinks were higher. Conclusions and potential relevance: A measurable effect of the conditioning exercise was demonstrated. The margin between too much and too little work when training foals may be narrower than intuitively presumed.