Laminitis is a serious hoof disease found in equines (e.g. horses, ponies, donkeys). Although it is very rare for laminitis to kill a horse directly, severe cases can result in the horse being put down for humane reasons (horse is in pain) or economic factors (horse is crippled and can no longer be used). Such euthanasia is sufficiently common that laminitis has become the second most common cause of premature horse death.

The term ‘laminitis’ refers to damage to the ‘laminae’, which is the connective tissues between the hoof bone (also known as the pedal bone) and the hoof wall. In mild cases of laminitis this tissue becomes inflamed and starts to break down. In more severe cases this connective tissue is sufficiently damaged that the hoof bone separates partly or completely from the hoof wall, rotating and sinking within the hoof. In extreme cases, the bone will actually penetrate the sole of the hoof. As the bone moves, it may also tear blood vessels and other tissues. Longer term, the damage to the hoof can result in permanent damage to the hoof growth and repair mechanisms, resulting in abnormal growth (e.g. flat or convex sole, rings in hoof wall, separation between hoof wall and sole).

One hears the term ‘founder’ in relation to ‘laminitis’. Unfortunately, not everyone uses the term in the same way. Some people use both terms interchangeably, while others use founder to describe the more serious cases of laminitis (e.g. bone penetration of the sole).

There are two main sources of damage to the laminae, leading to laminitis. One is toxins, which enter the blood and travel to the laminae, where they cause inflammation and tissue breakdown. The other is mechanical, where the laminae is damaged due to repeated shocks to the hoof (e.g. from running or jumping on hard surfaces).

Excessively rich feed results in changes to the bacteria population in the digestive system, causing the release of toxins by the bacteria. It occurs when a horse has too much carbohydrates or nitrogen, either from excessive amounts of rich feed (e.g. grain) or lush pasture. Pasture is most likely to be excessively rich in spring, when rain follows a drought, or if it has been fertilized. As some breeds (in particular, ponies) are more sensitive than others, one should take special care with sensitive breeds to restrict the amount of rich food and to keep them off rich pasture. Alternatively, one can put them on pasture for a limited time but use a grazing muzzle to restrict the amount they eat.

Mechanically caused laminitis most often occurs in competition horses, such as jumping horses or race horses, which are worked on hard ground. However, it can also occur to pleasure horses, if they are worked or travel on hard surfaces. One should try to avoid use of a horse on hard surfaces and when it is necessary to travel on hard surfaces try to reduce the pace as a walking horse will have less shock to its feet than a running horse. Ensure that the feet are correctly trimmed; in particular avoid over-trimming or trimming for long toes as these reduce the shock resistance of the feet. If the horse has shoes, ensure that the shoeing is done by a competent professional. Shock absorbing shoes (e.g. horse shoes with a rubber component) and boots are increasingly used, even in competitive sports, to reduce not only the risk of laminitis but also other shock related injuries.

The third major cause of laminitis is toxins which are unrelated to overly rich feed. This includes toxins which are ingested (e.g. through moldy hay, or grass which has been treated with herbicides) or toxins which are produced due to an infection within the horse. Ensure that food does not contain fungus, mold or chemicals. Ensure that any infections are promptly and aggressively treated, before they can result in toxin overload leading to laminitis.

Doug Stewart is the author of Laminitis and Founder.

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