The modulus of elasticity of equine hoof wall: implications for the mechanical function of the hoof.

The research article investigates the differences in elasticity in various parts of horse hooves and their correlation to patterns of deformation observed in these animals. The findings suggest that different areas of the hoof wall have varying stiffness, which may be structurally essential for stress dispersion during weight bearing in horses.

Research Objectives and Methodology

• The primary objective of the study was to understand if there are regional differences in the modulus of elasticity (a measure of the stiffness of a material) in the horse hoof wall.
• The researchers also sought to correlate these elasticity variations with changes observed in the hoof during normal weight-bearing and locomotion.
• The modulus of elasticity was determined for both tension (stretch) and compression (squeeze) for samples collected from six horse forefeet.
• These samples were tested from various points along the hoof wall, including the middle of the inner and outer wall halves, the lateral and medial quarters, and two positions along the dorsal wall. The samples were also oriented both parallel and perpendicular to the tubules, the tiny structures that characterize the hoof wall’s microstructure.
• The research team also noted the color of each sample and measured the moisture content.

Findings and Interpretations

• The mean values for the modulus of elasticity ranged between 460-1049 MPa, with the outer dorsal wall showing the highest values and the inner dorsal wall the lowest. The lateral and medial quarters had intermediate values.
• At all sites, the modulus of elasticity was slightly higher under compression than tension, suggesting potential microstructural defects.
• The stiffness difference between the outer and inner wall was found to be correlated inversely with moisture content.

Implications

• The disparity in stiffness between the outer and inner hoof wall suggests that horse hooves have a notably rigid external shell with a softer interior layer. This structural arrangement may protect the delicate tissues residing internally from stress.
• The similarity in stiffness between the samples from the quarters and the mean values from the two dorsal wall sites indicates that the quarter wall has similar stiffness variation across its thickness as the dorsal wall. However, due to its reduced thickness, the quarters are functionally more flexible than the dorsal wall. This facilitates the flaring of the lateral and medial walls under weight-bearing.
• Horn pigmentation was found not to affect hoof stiffness, contradicting popular beliefs that white hooves are mechanically inferior.