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Laminitis and Its Causes

Knowing the causes can help minimize the risk.

Laminitis, or inflammation of the laminae that attach the horny hooves to the sensitive internal structures of the foot, is a serious cause of lameness and reduced performance in horses. Typical signs of early, or acute, laminitis (also called “founder”) include a horse’s reluctance to turn or pick up its feet and a “walking on eggshells” gait. The feet may feel warm, and the digital pulses in the pastern are increased. Severely affected horses are reluctant to move at all and may lie down much of the time. Horses with chronic laminitis often show growth rings on the hoof that widen at the heel, and ponies’ feet may develop an “elf shoe” appearance. Causes include:

1. Carbohydrate Overload: Horses can founder if they get loose and gorge on grain or are suddenly switched to a new rich diet. Laminitis is also common in the spring or after a period of heavy rain when horses or ponies consume lush pasture.

2. Endotoxemia or Infection: Laminitis is a big worry whenever any horse suffers severe inflammation of the intestine, bloodstream, or uterus. Potomac horse fever, colic surgery, and retained placentas in foaling mares are all problems that can cause laminitis because circulating toxins can result in severe hoof damage.

3. Support Laminitis: Any horse that bears most of its weight on one leg because of severe lameness or a fracture in the other leg is at constant risk for developing laminitis in the supporting leg.

4. Black Walnut Shavings: Black walnut wood contains a potent toxin called juglone that can induce laminitis in horses just hours after exposure. Even a 10% concentration of black walnut shavings in a load of bedding can potentiate the problem.

5. Trimming the Hooves Too Short or Excessive Road Concussion: Bruised soles that result
from excessive concussion or a radical trim can cause laminitis.

6. Pituitary Adenomas (Cushing’s Disease): These tumors, common in aged horses with long, curly hair coats, are often associated with a chronic, insidious form of laminitis that can be debilitating and very difficult to treat.

In addition to the above direct causes, many risk factors have been identified for laminitis. The most common factor is obesity, especially if it is associated with a heavy, cresty neck and low circulating thyroid hormone (T4). Some horses develop laminitis as a reaction to certain medications. Systemic corticosteroid treatment carries a slightly increased risk of laminitis. Certain breeds of horses are more prone to the condition than others, and ponies are notorious for foundering on lush grass.

Some horses do founder for no apparent reason at all, but many others can be linked to a direct cause such as contact with black walnut or grazing in a lush pasture. Understanding and avoiding the above risks whenever possible is important for every horse owner as treatment of laminitis is expensive, time consuming, and sometimes unrewarding.

Look at your own situation and assess your risk factors—if your horse is heavy, put him on a diet! Be careful of lush pasture grazing, and keep those grain bins securely locked. Assure that all foaling mares deliver their placentas within a few hours of foaling, and if your “senior citizen” is suddenly looking like a shaggy dog, call the vet to test for Cushing’s disease. And if your horse does show signs of laminitis, seek veterinary help right away!

laminitis

This stance is typical of a horse with severe laminitis. Notice how he has shifted his weight to his hindquarters to minimize the pain. Illustration from The Handbook of Horseshoeing, Dollar, 1898.

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