The influence of exercise during growth on ultrasonographic parameters of the superficial digital flexor tendon of young Thoroughbred horses

Abstract

Reasons for performing study: Conditioning by early training may influence the composition of certain musculoskeletal tissues, but very few data exist on its effect during growth on tendon structure and function.

Objectives: To investigate whether conditioning exercise in young foals would lead to any ultrasonographically detectable damage to the superficial digital flexor tendon or an increase in cross-sectional area (CSA).

Methods: Thirty-three Thoroughbred foals reared at pasture were allocated to 2 groups: control (PASTEX) allowed exercise freely at pasture; and CONDEX, also at pasture, began conditioning exercise from mean age 21 days over 1030 m on a purpose-built oval grass track, for 5 days/week until mean age 18 months. Foals were observed daily, and underwent orthopaedic examination monthly. Ultrasonographic images of the superficial digital flexor tendon (SDFT) at the mid-metacarpal level of both forelimbs were obtained in all foals at ages 5, 8, 12, 15 and 18 months. CSA was validated (r2 = 0.89) by determining CSA from digital photographs of the transected SDFT surface from 12 of the horses necropsied at age 17.1 months.

Results: There was no clinical or ultrasonographic evidence of tendonopathy in either group and the greatest increase in mean CSA in both groups occurred between age 5 and 8 months. Across all age categories, there was no significant difference in mean CSA between the left and right limbs, or colts and fillies; there was a trend towards a larger CSA in the CONDEX group (P = 0.058).

Conclusions: There was no conclusive evidence for a structural adaptive hypertrophy of the SDFT, probably because the regimen was insufficiently rigorous or because spontaneous pasture exercise may induce maximal development of energy storing tendons.

Potential relevance: A moderate amount of early conditioning exercise against a background of constant exercise at pasture is not harmful to the development of the flexor tendons.