Depending on the severity, horses with founder, also called laminitis, are reluctant to move and may appear to walk on eggs when they do. The foot may feel warm to the touch, and the horse may appear anxious and tremble.
The pain that causes the reluctance to move and the warmth of the foot results from swelling (inflammation) of the tissue (the laminae) between the foot bone and the wall of the hoof. When this soft tissue swells, it is compressed between the hard underlying bone and overlying hoof. If the swelling is severe, blood flow to the laminae may stop, and the tissue may die. When this happens, the laminae separate and the foot bone becomes disconnected from the hoof and may rotate downward, while the tip of the hoof wall curls upward.
Many causes of founder are recognized that are not related to nutrition, including running on hard ground, abortion, high fever, infections, retained placenta, and exposure to some drugs. Nutritional causes of founder include rapid consumption of excessive amounts of grain, of cold water after exercise, or of lush grass or legume pastures.
If one of these circumstances has occurred, a veterinarian should be called at once, before signs develop, to care for the animal. Like obesity, founder can be difficult to treat and is better prevented. Locking up grains, cooling horses out before permitting access to water, feeding hay to decrease appetite before horses are turned out onto lush pastures, and providing restricted access to such pastures should prevent most diet-related cases of founder.