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’ comes from ‘laminae’, which is the tissue which connects the hoof bone (correctly known as the pedal bone) to the hoof wall. Damage to this tissue is known as ‘laminitis’. In mild cases the tissue becomes inflamed and begins to break down, reducing the strength of the bone-wall connection. In more severe cases the connection is reduced to the point that the bone begins to move, rotating within the hoof and sinking down. In extreme cases, the hoof will actually go through the sole of the hoof. As the bone moves, it can cause further damage to blood vessels and other surrounding tissues. Longer term, this damage affects the hoof repair and growth mechanisms, resulting in various types and degree of abnormal growth (e.g. convex or flat sole, hoof wall rings, separation of sole and hoof wall). In mild cases, the horse can return to normal activities. In more severe cases, the horse will need to be retired or put down.

The term ‘founder’ is associated with laminitis but can be used in several different senses. Some people use founder as the lay term for laminitis, while others use it to describe the more serious forms of laminitis (e.g. when the pedal bone penetrates 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.

Competition horses, such as jumping or racing horses, which are frequently worked on hard ground, are relatively likely to eventually develop laminitis. However, it can also occur in pleasure horses, if they work or travel on hard surfaces. Try to avoid use of your horse on hard ground. If it is necessary to travel on hard surfaces, try reducing the pace since a walking horse will have less hoof shock than a running horse. Ensuring that hoof trimming is correctly done, especially avoid trimming for long toes or over-trimming as these reduce the ability of the hooves to absorb shocks. If the horse is shoed, it should be done by a competent professional. Consider using shock-absorbing shoes (e.g. horse shoes with a rubber component) or shock absorbing boots during competitions (both are increasingly being used, even at the professional level).

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.

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