THE MODULUS OF ELASTICITY OF EQUINE HOOF WALL - IMPLICATIONS FOR THE MECHANICAL FUNCTION OF THE HOOF

During normal weight-bearing and locomotion, the equine hoof wall defo rms in a consistent pattern: the proximal dorsal wall rotates caudo-ve ntrally about the distal dorsal border and there is latero-medial flar ing posteriorly. The aim of this study is to examine whether there are regional differences in the modulus of elasticity of hoof wall materi al and whether such differences correlate with the pattern of deformat ion which occurs in vivo. The modulus of elasticity of equine hoof wal l was determined in tension and compression for samples from six foref eet. Samples were tested at the mid-point of the inner and outer halve s of the wall thickness at two positions along the proximo-distal axis of the dorsal wall, and from the mid-point of its thickness at the la teral and medial quarters, Test samples were oriented both parallel an d perpendicular to the tubules that characterise the microstructure of the wall, The colour of each sample was noted, and the moisture conte nt measured.The range in the mean modulus of elasticity for all sample s and tests was 460-1049 MPa, the dorsal outer wall having the highest values, the dorsal inner wall the lowest, and the quarters having int ermediate values, The mean value obtained for the quarters was similar to the average of the values for the dorsal inner and outer walls, At all sites, the modulus of elasticity was marginally higher in compres sion than in tension, possibly owing to microstructural defects, The d ifference in stiffness between the outer wall and the inner wall was i nversely related to moisture content. The difference in stiffness betw een the dorsal outer and inner walls demonstrates that the equine hoof wall has a comparatively rigid external capsule with a lining of lowe r stiffness, This arrangement presumably provides some stress protecti on to the internally adjacent living tissues, The similarity in stiffn ess between the samples from the quarters and the mean of the two dors al wall sites suggests that the wall at the quarters has a similar cha nge in stiffness across its thickness as the dorsal wall, However, the reduced thickness of the wall at the quarters compared with the dorsa l wall means that, functionally, the quarters are more flexible than t he dorsal wall, This will facilitate the flaring of the lateral and me dial walls which occurs during weight-bearing, Anisotropy was evident only in tensile tests of the dorsal wall samples, Contrary to popular assertions that white hooves are mechanically inferior, horn pigmentat ion had no detectable effect on stiffness.