EFFECTS OF TRAINING ON COLLAGEN FIBRIL POPULATIONS IN THE SUSPENSORY LIGAMENT AND DEEP DIGITAL FLEXOR TENDON OF YOUNG THOROUGHBREDS

Objective-To determine the effect of a specific galloping exercise reg imen on collagen fibril mass-average diameters (MAD) in the deep digit al flexor tendon (DDFT) and suspensory ligament (SL) of young Thorough breds. Animals-12 Thoroughbred fillies, 21 +/- 1 (mean +/- SD) months old. Procedure-6 horses underwent a specific 18-month treadmill traini ng program involving galloping exercise. The remaining 6 horses served as controls, undertaking low-volume walking exercise over the same pe riod. Sections were excised from the midpoint of the DDFT and SL, and small strips were dissected from central and peripheral locations for each structure. Fibril diameters were measured from micrographs of tra nsverse ultrathin sections, using a computerized image analysis progra m. An MAD value was calculated for the central and peripheral regions of the DDFT and SL for each horse. Values for both regions were compar ed between exercised and control horses. Results-The MAD did not chang e significantly with exercise for either the DDFT or the SL. Conclusio n-Loading of the DDFT as a result of this exercise regimen was not suf ficient to stimulate collagen fibril hypertrophy, in keeping with curr ent data that indicate this tendon, compared with the SL and superfici al digital flexor tendon (SDFT), is subjected to low loads. Microtraum a, in terms of reduction in fibril MAD, may have occurred in the SL at a site different from that sampled. Another possibility is that, betw een the trot and the gallop, loading of the SL does not increase to th e same extent as that of the SDFT.