Laminitis is a crippling disease of the equine hoof, says the Merck Veterinary Manual. The laminae that attach the hoof wall to the distal phalanx fail. Often the distal phalanx is displaced by the weight of the horse, causing severe lameness.
There are multiple causes of laminitis. One of the most common is a metabolic disorder seen in overweight horses and ponies, particularly when they are grazed on rich pastures. Diseases associated with sepsis or toxemia, such as colic, a retained placenta, or ingestion of large quantities of grain, commonly lead to laminitis. Placing excessive weight on one limb due to injury can cause laminitis as well.