Wet-Dry Cycles - Effect on the Hoof
Winter is coming and with it comes the rain and mud and boggy fields. The reality is in the wild horses would never choose to stand in saturated ground, they would roam and find more suitable grazing areas. As we enter these wetter months what should we know about the effects of the wet and often wet-dry cycles, on our horses feet?
To answer this we need to have a basic understanding of the composition of the hoof wall and then explore its response to hydration.
Fig.1 The composition of the hoof wall as it grows from the coronary papillae.
The hoof is made from keratin cells that go through a cycle of programmed cell death, called apoptosis. This means that the external hoof wall is essentially dead tissue and as such has no ability to heal or regulate itself. It therefore becomes a product of its environment. Fig. 1 shows how the cells proliferate from the germinative layer, forming tubules in a bed of undefined structure or rather a series of (crystalline) tubules within an (amorphous) matrix.
Under normal conditions the stiffness and hardness of the tubular areas are greater than in the inter-tubular areas. This indicates that the tubules serve as reinforced structures to support the compressive load created between the weight of the horse and the ground.
However, studies have shown us that the mechanical properties of the hoof are directly affected by the moisture content. A certain amount of moisture is documented as being important for the flexibility of the hoof, keratin materials are brittle without water molecules to plasticize the material. However, excessive soaking has been said to cause the hoof to become too flexible affecting its load bearing capabilities and possibly leading to increased plastic (permanent) deformation over the hoofs natural elastic (temporary) deformation under load.
It is the reinforcing mechanism of the tubular horn that has been shown to be affected with over-saturation of the hoof. Studies have shown us that both the tensile strength and hardness in the tubular and inter-tubular areas decreased significantly after full hydration. Even more interestingly and perhaps relevant is that the stiffness and hardness of tubules become less than in the inter-tubular areas, which is due to the higher water absorption in the tubular areas, this means these structures lose their reinforcing characteristic. A study showed that in a fully saturated hoof sample, the tensile strength and hardness decreased by as much as 98%. In reality a hoof would probably not reach that level of saturation but it illustrates possible implications of leaving our horses out in boggy fields.
So what does this actually mean?
In essence the hoof does become softer and less able to support the weight of the animal above it, it is more likely to collapse/flare. Soft, shod hooves that are taken from a wet environment and hacked down the road may have their shoes become loose