The stratum medium of the equine hoof wall is a keratinized tissue with material characteristics and material properties that facilitate the accommodation of forces associated with static and dynamic weight bearing. The mechanical properties of keratinized structures are modulated by their hydration state.1–3 Water content affects the stiffness and fracture resistance of the hoof wall.1 Although excessive dehydration causes fractures in the hoof, swelling attributable to excess water absorption into the hoof wall is linked to a high incidences of hoof damage.4 In other studies,1,5,6 the water content of the hoof wall has been examined by gravimetric changes via various drying techniques because limited methods exist for determination of water distribution in the tissue. It is difficult to detect localization patterns for water in specimens with these techniques. Therefore, we attempted to use NMR microscopy, which can reveal water localization through visual results.
Nuclear magnetic resonance microscopy is a method that provides enhanced spatial resolution because of the use of a strong static magnetic field and high magnetic field gradients. In NMR microscopy, spatial resolution is provided to submillimeter dimensions,7,8 whereas that in traditional MRI is on the order of 1 mm. Magnetic resonance imaging, including NMR microscopy, is suitable for visual localization of water molecules in tissue specimens.
Magnetic resonance imaging or NMR microscopic investigation of equine hoof specimens has been reported.9,10 In these studies,9,10 the lamellae of the inner hoof wall (stratum internum) and the coronary papillae of the coronet were clearly visible; however, structures in the stratum externum and stratum medium of the hoof wall were less clearly visible. The stratum medium has a characteristic structural organization of individual horn tubules surrounded and separated by intertubular horns. The horn tubules are elongated cylinders approximately 0.1 to 0.2 mm in diameter that morphologically consist of 2 components: the outer circular layer, known as the cortex, and the central area (marrow). These tubules are believed to be involved in regulating the mechanical properties of the hoof wall as well as the gradient of water content11 and water transfer12 in the hoof wall on the basis of their morphology and distribution pattern. These beliefs raise the possibility that water distribution in the hoof wall may be associated with these tubules; however, the relationship of horn tubules to water distribution or permeation in the hoof wall has not been determined, but has been evaluated via an indirect observation with horseradish peroxidase as a water-soluble tracer.13
The objective of the study reported here was to determine via sequential NMR microscopic observations the distribution of water in equine hoof wall specimens and changes in this distribution during hydration. The process of water absorption from the surface of the horn specimen contacting the water and the relationship between the absorption pattern of the horn tubules and intertubular horns in this process were analyzed to assess the involvement of horn tubules in water transfer.
Nuclear magnetic resonance
2114C, Makita Co Ltd, Aichi, Japan.
Parafilm, Pechiney Plastic Packaging Inc, Chicago, Ill.
NM-AIM imaging equipment, JEOL, Tokyo, Japan.
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