In vitro effect of horseshoe length on hoof wall deformation, expansion, and strain

Shoeing techniques have the potential to affect hoof growth, causing abnormal hoof conformations, which in turn put affected horses at risk for lameness and injury. Racehorses are often shod with shorter shoe branches which may predispose them to underrun heel hoof conformation. Horseshoe branch length was tested to determine the effect on hoof wall deformations, expansion, strain and fetlock extension during midstance limb loading. Our hypotheses were that shortening of the shoe branch length would increase fetlock extension, increase compressive strains at the heel, and change principal strain directions in a proximodorsal direction. Nine cadaveric forelimbs were loaded in vitro to simulate mid-stance from walk to canter loads. Analysis of variance was used to assess the effect of horseshoe (no shoe, short shoe, full shoe, and long shoe) on outcome variables. Hoof wall expansion and lateral hoof wall distortion did not differ among treatments. Principal compressive hoof wall strain magnitudes were greater than principal tensile strain magnitudes. As shoe length increased principal compressive strains decreased, except for the middle quarter location; shear strains increased for distal locations and decreased at the proximal heel location; and principal strain directions viewed on the lateral side of the right hoof rotated in a counterclockwise direction at middle and distal quarter locations. Results do not provide evidence that a shorter shoe increases fetlock extension. Additionally, as the shorter shoe had similar strain results to that of an unshod hoof, it is unclear if a shorter shoe could lead to the development of abnormal hoof conformations. Other factors that may play a role in changes of hoof conformation including surface type, amount of exercise and frequency of trimming as well as other planes within the xyz coordinate system for the fetlock and hoof should be investigated.