The effect of loading upon hoof wall growth and hoof shape in the Thoroughbred foal

Abstract

The hoof wall is adapted to take most of the weight-bearing of the foot and is anisotropic and homogeneous. Foals appear to be born with symmetrical paired feet which by maturity are frequently unequal in angle and width. They stand within minutes of birth subjecting the hoof wall to loading. Hoof growth rate and hoof compression may be factors affecting hoof shape. The effect of conformation changes during maturation upon loading and differential hoof growth was unknown. The aims were to; quantify and evaluate the epidermal structure, hoof growth rate, hoof renewal, dorsal hoof wall angle, plastic hoof compression, and hoof loading, during paediatric development.
Hoof growth rate, renewal, and hoof angle were recorded in foals (n=80) and weanlings/yearlings (n=12) and the hoof wall structure of histological samples of fetuses and paediatric foals (n=15) was determined. Solar loading, hoof growth, and hoof angle was recorded in healthy foals (n=18) and compared to a group with acquired flexural deformity (n=9).
Horn tubule size and number increased significantly, and density decreased significantly during maturation. The dorsal hoof wall angle declined with age. Hoof renewal in newborn foals was 145±15 days whereas weaning/yearlings were 283±26 days. A relationship between plastic hoof compression and time was found (r = 0.46, P = 0.002). Hoof compression in foals was 0.039±0.022mm per day and in weanling/yearlings 0.03±0.016mm per day. Hoof growth rate, hoof compression, and dorsal hoof wall angle, all correlated to ageing and differed between the healthy and acquired flexural deformity foals.
The original findings in this thesis give a broad understanding of the developing equine hoof wall. Knowledge of renewal times allows predictions of healing in cases of partial hoof wall avulsion. Original data recording the structure of the developing hoof wall may lead to a greater understanding of its response to loading, while improved recognition of the angles of the digit and hoof during maturation will allow a more accurate assessment of conformation. Hoof distortion is affected by loading, hoof compression and hoof growth and comprehending the link between these factors may lead to enhanced treatment strategies for all ages of horse.