Equine hoof mechanics and function have been investigated for many years. One of the most reliable methods with which to assess hoof wall distortion is extensometry, a technique that uses electrical resistance strain gauges to identify changes in length of a given material (ie, a measurement of its deformation). In such circumstances, the forces acting on the surface of the material are translated into compressive (negative) or tensile (positive) strains.
Investigation of forelimb hoof wall strains in equids has led to the description of a pattern of deformation that is widely accepted. During stance, the front hoof wall is predominantly under compression. There is a palmar movement and flattening of the dorsal wall and flaring of the quarters, and the combination of these movements causes biaxial compression at the toe.1,a Compressive strains increase following impact and reach a peak close to midstance, before decreasing to the initial values. However, most of the information collected to date relates to horses that were walking and trotting at low speeds or, rarely, cantering slowly. There is little information as to how the front hoof responds to loading at high speeds,2 to our knowledge.
The relationship between equine hoof strains and shape has also been investigated and is not a simple issue. Various studies3–6 have revealed conflicting findings concerning the effect of TA on front hoof wall strains. Although results of a study3 indicated that strains decreased dorsally and increased laterally and medially with increasing TA, other investigations4,5 have provided data indicative of different effects. More recently, the redistribution of strains with unloading of the medial side at the expense of the lateral side of the front hoof with increasing TA at the trot has been proposed.6
Toe angle has been shown to decrease over time in exercising racehorses7 and warmbloods.8 In a study9 involving Standardbreds, TA increased following a period of mild trotting exercise, but that effect could not be related to exercise, given that similar changes were observed in nonexercised horses in the control group. These studies7–9 involved primarily the forelimb hooves of hoof-trimmed and shod horses, implying some degree of human-induced hoof changes. Toe angle changes in untrimmed unshod horses that undergo exercise have not been reported, to our knowledge. A decrease in the PHC of the forelimb hooves of racehorses in training has also been observed,10 but a pilot studyb investigating the same variable in the forelimb hooves of unshod horses exercised at various gaits on a treadmill failed to produce conclusive results.
The purpose of the study reported here was to investigate forelimb hoof wall strains and shape changes in unshod horses undergoing regular moderate exercise on a treadmill at selected speeds and gaits. The intent was to test the hypothesis that the pattern of deformation of the forelimb hoof wall during high-speed exercise would be the same as that found during low-speed exercise. Second, variation in TA and PHC in untrimmed unshod horses in response to a regular exercise regimen that included medium-rate galloping was investigated. Third, the effect of forelimb hoof shape changes on hoof wall strains was assessed to determine whether strains remained consistent in an individual horse despite a change in hoof shape.
Minimum principal peak strain
Minimum principal midstance strain
Proximal hoof circumference
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