Douglas J E, Mittal C, Thomason J J, Jofriet J C
Equine Research Centre, University of Guelph, Ontario, Canada.
J Exp Biol. 1996 Aug;199(Pt 8):1829-36. doi: 10.1242/jeb.199.8.1829.
During normal weight-bearing and locomotion, the equine hoof wall deforms in a consistent pattern; the proximal dorsal wall rotates caudo-ventrally about the distal dorsal border and there is latero-medial flaring posteriorly. The aim of this study is to examine whether there are regional differences in the modulus of elasticity of hoof wall material and whether such differences correlate with the pattern of deformation which occurs in vivo. The modulus of elasticity of equine hoof wall was determined in tension and compression for samples from six forefeet. Samples were tested at the mid-point of the inner and outer halves 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 lateral and medial quarters. Test samples were oriented both parallel and perpendicular to the tubules that characterise the microstructure of the wall. The colour of each sample was noted, and the moisture content measured. The range in the mean modulus of elasticity for all samples and tests was 460-1049 MPa, the dorsal outer wall having the highest values, the dorsal inner wall the lowest, and the quarters having intermediate 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 compression than in tension, possibly owing to microstructural defects. The difference in stiffness between the outer wall and the inner wall was inversely related to moisture content. The difference in stiffness between the dorsal outer and inner walls demonstrates that the equine hoof wall has a comparatively rigid external capsule with a lining of lower stiffness. This arrangement presumably provides some stress protection to the internally adjacent living tissues. The similarity in stiffness between the samples from the quarters and the mean of the two dorsal wall sites suggests that the wall at the quarters has a similar change in stiffness across its thickness as the dorsal wall. However, the reduced thickness of the wall at the quarters compared with the dorsal wall means that, functionally, the quarters are more flexible than the dorsal wall. This will facilitate the flaring of the lateral and medial 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 pigmentation had no detectable effect on stiffness.
在正常负重和运动过程中，马蹄壁会以一致的模式变形；近端背侧壁围绕远端背侧边缘向尾腹侧旋转，且在后方有内外侧扩张。本研究的目的是检查马蹄壁材料的弹性模量是否存在区域差异，以及这种差异是否与体内发生的变形模式相关。对来自六只前蹄的样本进行拉伸和压缩试验，测定马蹄壁的弹性模量。在背侧壁近远轴线上的两个位置，分别在壁厚内外半部分的中点进行测试，以及在外侧和内侧四分之一处的壁厚中点进行测试。测试样本的方向既平行又垂直于表征壁微观结构的小管。记录每个样本的颜色，并测量其含水量。所有样本和测试的平均弹性模量范围为460 - 1049兆帕，背侧外壁的值最高，背侧内壁的值最低，四分之一处的值居中。四分之一处获得的平均值与背侧内外壁值的平均值相似。在所有部位，压缩时的弹性模量略高于拉伸时，这可能是由于微观结构缺陷。外壁和内壁之间的刚度差异与含水量呈负相关。背侧外壁和内壁之间的刚度差异表明，马蹄壁有一个相对刚性的外部包膜，其衬里刚度较低。这种结构大概为内部相邻的活组织提供了一些应力保护。四分之一处样本的刚度与两个背侧壁部位平均值之间的相似性表明，四分之一处的壁在整个厚度上的刚度变化与背侧壁相似。然而，与背侧壁相比，四分之一处壁的厚度减小意味着，在功能上，四分之一处比背侧壁更灵活。这将有助于在负重过程中发生的外侧和内侧壁的扩张。各向异性仅在背侧壁样本的拉伸试验中明显。与普遍认为白色蹄在机械性能上较差的观点相反，角色素沉着对刚度没有可检测到的影响。
