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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 horse hoof contains connective tissue which holds the hoof bone (the pedal bone) in place and connected to the hoof wall. This tissue is known as laminae and if it becomes damaged the result is known as ‘laminitis’. Minor damage results in inflammation of the tissue and temporary pain. More severe cases reduce the strength of the connective tissue, allowing the pedal bone to rotate and sink within the hoof. In the most extreme cases, the pedal bone will actually penetrate the sole of the hoof and be visible. In mild cases the horse can return to normal duties but in more severe cases (depending on the amount of rotation and sinking of the pedal bone) the horse will have to be retired, with the worst cases requiring that the horse is immediately put down. Although there are a number of treatments for laminitis, once the damage is done they can provide only minor improvements, so the emphasis needs to be on prevention rather than treatment.

The term ‘founder’ is related to ‘laminitis’, but is used in different ways by different people. Some people use the term founder interchangeably with laminitis, others to describe the more advanced forms of laminitis (e.g. substantial hoof bone movement or the bone penetrating the sole).

There are three main causes of laminitis. The first is toxins from excessively rich feed, the second is mechanical separation and the third is toxins from internal infections or external poisoning. In both toxin categories, the toxins are carried through the blood stream to the laminae, where they cause inflation and tissue breakdown. The mechanical category is associated with laminae damage through repeated shocks to the hooves (e.g. from jumping or running 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.

Ensure that your horse goes not get external toxins from food which has mold, fungus or chemicals. Do not let them eat grass which has been chemically treated (e.g. with herbicides). Any serious infections should be promptly and aggressively treated, to prevent the infection from releasing toxins into the blood.

This Laminitis and Founder article is part of the Horse Care series by Dr. Doug Stewart

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