The best way to understand laminitis, or founder, is to think of the healthy coffin bone as "Velcroed" to the inside of the hoof wall by interlocking sensitive and insensitive laminae. When the Iaminae become inflamed, they start to break down--and your horse is said to have laminitis.
As long as the inflammation is mild (as it might be from a stone bruise, say), it's no big problem. But if enough cell death occurs to damage or destroy the interlocking bond between the hoof wall and the coffin bone, the coffin bone can start to rotate, That's when things get serious, with your horse developing one of two conditions:
Acute Founder can result when a healthy horse gets into the grain, has a bad drug reaction, suffers repeated concussion on hard surfaces, undergoes colic surgery, gets exposed to black-walnut wood, or has a leg injury or unsoundness that creates a load-bearing trauma on the other leg. If you and your vet can identify one of these causes, your horse has acute founder. Either he'll get better or he won't (he may do OK for a while, then crash), but you'll usually know within several weeks--days in some cases.
Chronic Founder is characterized by more persistent changes in hoof-wall structure and blood supply. It tends to have a metabolic or hormonal basis (as in Cushing's Disease, a pituitary-gland disorder in which chronic founder is a typical development). It can result from long-term extreme stress from showing, or prolonged medication, or--and this is pretty new thinking--insulin resistance, a condition I liken to human diabetes. Insulin resistance is caused by an inability of insulin to carry glucose into the muscle cells, where it can be used as fuel; this results in a partially reduced ability to utilize carbohydrates. In human diabetes, one complication of insulin resistance is degenerative changes in the small blood vessels?an effect similar to degeneration in the laminae of the foot in horses.
If you and your vet can identify one of the above causes, or if you can't say why your horse has foundered, he's in the chronic category. Although chronic founder can come on suddenly, you may end up struggling with it for years. It may stabilize, improve enough for your horse to function in reasonable comfort, worsen gradually, or vary from day to day or week to week, possibly with repeat acute bouts.
This article apeared in the August 2002 issue of Practical Horseman magazine.