Abstract:
The aim of this investigation was to investigate the possible influence of early conditioning exercise on the 18-months old Thoroughbreds in terms of lesion development, extracellular matrix and histomorphometric changes in the cartilage and subchondral bone of the midcarpal joint. 12 Thoroughbreds were divided equally into two groups; a treatment (CONDEX) and a control group (PASTEX) at birth. Both were raised in free pasture conditions from birth for 18 months before euthanasia with the CONDEX only receiving the additional imposed exercise from birth. At the end of the trial, both the CONDEX and PASTEX horses were euthanized and their midcarpal joints were harvested. The investigation involved i) mapping and characterising the gross lesions in the midcarpal joint with respect to known sites of high stress and vulnerability, ii) measuring swelling strains in the cartilage matrix with respect to depth from different topographical regions, iii) histomorphometrically quantifying the area and thickness of hyaline and calcified cartilage and vasculatures, while also measuring the preferential angles of the collagen fibrils in these zones, and counting the number of vascular channels proximal to the cement line as well as measuring the cement line irregularity itself. Both the CONDEX and PASTEX were found to contain five different categories of lesions with similar levels in each category. However, the number of sites affected by mild traumatic osteochondrosis was lower in the CONDEX. There was no detectable exercise effect in the extracellular matrix swelling behaviour (P = 0.795) and neither was the overall histomorphometry (P = 0.4271). Conversely, in the CONDEX, the vascular channel area (VCa) showed a significant exercise effect (P = 0.0461) while the histomorphometric variables were found to be highly correlated to each other (P = 0.052). These findings suggest that the imposed early exercise may have resulted in a lower number of mild osteochondrosis lesions in the dorsal region of third carpal bone while significantly increasing the overall subchondral vascular activity and the development of a coherent tissue response between the hyaline cartilage, calcified cartilage and the vascularity. In conclusion, the findings of this study together with those of others [1-3] suggest that early exercise induced a positive response in the CONDEX without increasing deleterious changes in the midcarpal joint when compared with the PASTEX. It is thus recommended that potential benefits of early exercise should be further explored.
