For horse owners, laminitis or founder can be tragic. “Many of these horses are eventually euthanized due to the chronic pain and the permanent deformity of their hooves,” said Dr. Heidi Ward, Arkansas Extension veterinarian.
Laminitis is inflammation of the lamina, which secures the hoof wall to the skin or dermis that sheathes the horse’s foot. Ward likened the hoof to a single human finger, where the fingernail is the wall, the nail bed is the securing lamina, and the connecting tissue is the subcutis, which attaches everything to the coffin bone. “Excessive inflammation causes degeneration of the lamina, so it is no longer allowing the wall to support the deep structures in response to force,” she said. “As a result, force makes the bone rotate, causing pain and lameness.”
One of the biggest causes of the affliction is diet. Horses can develop laminitis from consumption of lush, green grasses or large quantities of soluble carbohydrates like grain, bread or even black walnut shavings. It can also be the result of systemic disease or severe injury that cause the animal to favor one limb and place more stress on others. Age is a factor as well, and Ward said horses greater than 20 years of age are three times more likely to develop laminitis.
A veterinarian can diagnose laminitis by looking at a radiograph, or X-ray; the higher the degree of rotation of the coffin bone, the worse the diagnosis. The vet also checks the palmar digital artery on the back of the hoof; if the pulse is bounding, that’s a sign that laminitis may be forming. Ward said non-steroidal anti-inflammatory drugs, vasodilators and anticoagulants can decrease the inflammation, and a cold compress along with corrective hoof trimming and shoeing can alleviate the pressure and pain.
As for prevention, “The best thing people can do for their horses is proper condition and care,” Ward said. Make sure hooves are trimmed properly; don’t let them get too much greens or grain. “And of course, if they become ill – particularly with colic or diarrhea – get treatment from the veterinarian right away, because they will already be in danger of laminitis at that point and can be monitored and started on therapy,” said Ward.
Dr. Philip Johnson, professor of equine medicine and surgery at the University of Missouri’s Veterinary Medical Teaching Hospital, said bouts with diarrhea or colic or consumption of rich food “cause a disturbance to the normal bowel functions, and in horses the foot is very sensitive to some of those disruptions, so inflammatory changes that result from intestinal disease often lead to laminitis.”
Some horses, but not all, respond to sugars in their food with high releases of insulin, which is toxic to the foot.
“It’s well recognized that as a general rule, horses are often being fed perhaps more grain or more nutritional energy than they really need for their level of activity,” Johnson told OFN. “Some horses, and especially ponies, are individually sensitive to sugar and starch levels, even in grass.” The susceptible animals’ access to rich spring grass should be restricted.
The Oral Sugar Test is the standardized way of evaluating whether an individual horse or pony in sensitive to ingested sugars. The animal ingests a small quantity of corn syrup, and its blood insulin level is measured; some horses have high insulin responses to the test, and can be identified as being at risk to laminitis.
The connection between insulin and risk of laminitis has only been known since 2007. Like humans with Type 2 diabetes, susceptible horses can be administered the drug metformin, which reduces sugar uptake by the bowel.
