Effects of exercise on the diameter of collagen fibrils in the central core and periphery of the superficial digital flexor tendon in foals

Objective-To determine the effects of exercise on collagen fibril diameter distribution In the superficial digital flexor tendon (SDFT) of foals. Animals-43 Dutch Warmblood foals. Procedure-From 1 week until 5 months of age, group-1 foals (n = 14) were ho used in stalls and not exercised, group-2 foals (14) were housed in stalls but were exercised, and group-3 foals (15) were maintained at pasture. Biop sy specimens were collected from the SDFT at 2 months, and 8 foals in each group were euthanatized at 5 months. Remaining foals were housed together i n a loose stall and paddock until euthanatized at 11 months. After euthanas ia, specimens were collected from the SDFT, all specimens were analyzed by use of electron microscopy. Collagen fibrillar index (CFI), mass average di ameter (MAvD), and area dependent diameter (ADD) were compared among groups . Results-Exercise-related differences in fibril distribution were not detect ed among groups at 2 months. At 5 months, ADD in peripheral specimens was s ignificantly greater in group 1 than group 3. At 11 months, MAvD in core sp ecimens was significantly less in group 3, compared with the other groups. However, in peripheral specimens, MAvD was significantly less in groups 2 a nd 3. Conclusions and Clinical Relevance-Collagen fibril restructuring in the SDF T of foals is In part an exercise-driven process. Withholding exercise may cause a delay in fibril development that can be partially overcome by Incre asing exercise at a later age. Exercise type may also affect remodeling of the SDFT In foals.