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DISEASES of the hoof capsule and associated internal structures represent a significant health concern in both pet and working donkeys. Degenerative conditions of the foot are very common in the UK donkey population, with laminitis accounting for 13 per cent of the cases euthanased at The Donkey Sanctuary each year. Before discussing these diseases in more detail, it is important to understand the normal anatomy and function of the donkey foot, as they differ considerably from those of the horse in several respects.
Normal anatomy
When compared to a horse, the donkey has a more upright hoof pastern axis and consequently the dorsal hoof wall tends to be more vertical. Fowler (1995) reported that the dorsal hoof wall is 5° to 10° more upright in the donkey. When looking at the solar surface, the frog tends to be more developed but the apex does not extend as far towards the toe ( Fig 1 ). This has implications for the positioning of foot supports in the management of laminitis, and will be discussed in more detail later. The sole is a 'U' shape that is slightly flared at the heels compared to the rounder shape of a horse's hoof. When viewed from the dorsal aspect, the hoof capsule is cylindrical compared with the conical shape of the horse ( Fig 2 ). This difference in shape means that the heels appear narrow and contracted in the normal animal. In contrast to the horse, when viewed from the solar surface, the thickness of the hoof wall is relatively constant from the toe to the heels (Reilly 1997). The sole is also reported to be thicker (Hopegood 2002).
The structural composition of the hoof wall and sole is also different. While the stratum medium does have a zonal pattern to tubule density, in the donkey this can be divided into three zones, whereas the horse has a four-zoned pattern (Hopegood 2002). The anatomical differences in shape and angle of the hoof between the two species may explain the differences in tubule organisation and may result in a different movement of the donkey capsule during weight bearing. The density of tubules also differs, with the donkey having a lower density of tubules. This may also be linked...