Laminitis and Founder in Horses: Causes, Early Signs and Long-Term Management

What happens inside the hoof

Inside each hoof, the coffin bone, the bone that gives the hoof its shape, is attached to the inner hoof wall by thousands of interlocking leaf-like folds called laminae. Think of them as Velcro holding the bone in place while the horse's whole weight presses down through it.

In laminitis, these laminae become inflamed and damaged, and the bond weakens. The tissue is trapped inside a rigid hoof capsule, so swelling has nowhere to go, which is part of why it's so painful.

If the bond fails badly, the coffin bone can:

• Rotate, with the tip pulled down and back by the tendon behind it, sometimes until it pushes through the sole.
• Sink, dropping straight down inside the hoof.

Founder is the term most people use for this structural damage. In everyday use, "laminitis" and "founder" are often used interchangeably, but laminitis is the disease process and founder is what can follow.

What causes laminitis

Researchers now group the causes into three main types.

Endocrine laminitis is by far the most common. It's linked to high insulin levels in the blood:

• Equine metabolic syndrome (EMS) affects many easy keepers. These horses often carry fat on the crest of the neck, around the tail head and behind the shoulder, and their bodies overreact to sugar and starch with a big insulin spike.
• PPID (Cushing's disease) in older horses also raises the risk, often through insulin problems. See senior horse care.
• The trigger is often sugary grass, especially in spring and fall, or a feed high in starch.

Inflammatory or septic laminitis follows a serious illness elsewhere in the body, such as severe colitis, a retained placenta after foaling, pneumonia, or a horse breaking into the feed room and gorging on grain.

Supporting-limb laminitis happens when a horse can't bear weight on one leg because of an injury, and the opposite foot is overloaded for weeks.

Hard work on hard ground, sometimes called road founder, can also cause it, though less commonly.

Which horses are at risk

• Ponies, miniature horses, donkeys and "easy keeper" breeds such as Morgans, Arabians, Paso Finos and many Quarter Horses
• Overweight horses, especially with a thick, hard crest on the neck
• Horses with diagnosed EMS or PPID
• Horses that have had laminitis before
• Horses switched suddenly onto lush pasture or grain

Early signs

Laminitis usually affects both front feet most, though it can hit all four. Watch for:

• Reluctance to walk, especially on hard ground or when turning. The horse may walk as though it's "on eggshells."
• Shifting weight from foot to foot.
• A rocked-back stance: front legs stretched forward, hind legs tucked under, trying to put weight on the heels.
• Warm hooves, compared to normal or to other horses.
• A strong digital pulse. Feel the back of the fetlock, on either side, where an artery runs down the leg. Normally the pulse is faint or hard to find. In laminitis it's often strong and bounding.
• Lying down more than usual, or not wanting to get up.
• Reluctance to lift a front foot for the farrier, because it puts more weight on the other painful foot.

Mild cases can look like general stiffness or sore feet after a trim. Take any of these signs seriously in an at-risk horse.

What to do right away

Laminitis is an emergency. Early treatment can limit damage to the laminae.

1. Call your vet the same day. They'll examine the horse, may take X-rays of the feet to look for rotation or sinking, and will start treatment.
2. Take the horse off grass and grain. Feed only plain grass hay, ideally soaked, until your vet advises otherwise.
3. Move the horse to a deeply bedded stall or small pen with soft footing, such as deep shavings or sand, so it can stand and lie down comfortably. Don't force it to walk.
4. Ice the feet if your vet recommends it. Standing the lower legs and feet in ice water in the early stage reduces damage in some types of laminitis.
5. Give pain relief only as directed by your vet.

Your vet and farrier may add frog and sole support with pads, special shoes or boots, and recheck X-rays over the following weeks.

Long-term management

Many horses recover from laminitis and return to work, but a horse that has had it once is at higher risk of a repeat. Long-term management focuses on the cause.

Diet

• Feed low-sugar hay. Have your hay tested. A common target for at-risk horses is under about 10 to 12 percent combined sugar and starch.
• Soak hay in cold water for 30 to 60 minutes, or warm water for less, if you can't find low-sugar hay. Soaking removes some of the sugar. Discard the soaking water.
• Avoid grain and sweet feed. Use a ration balancer or a vitamin and mineral supplement to supply nutrients without calories.
• Feed by weight. For overweight horses, around 1.5 percent of body weight in hay a day, spread out in a slow feeder or hay net. See how much to feed a horse.

Grass

• Limit grazing or keep the horse in a dry lot during high-risk times.
• Use a grazing muzzle, which lets a horse graze and move with the herd while cutting how much it eats.
• Be careful in spring and fall, and on sunny days after cold nights. Grass stores the most sugar then, often peaking in the afternoon.

Weight and exercise

• Get overweight horses to a healthy weight, slowly, under your vet's guidance.
• Exercise once the feet are sound. Regular exercise improves how the body handles insulin.

Medical care

• Test for EMS and PPID. Your vet can measure insulin and other hormones. PPID is treated with daily pergolide.
• Keep regular farrier visits. A short toe and supported heel reduce the leverage on the laminae. See hoof care and trimming.

Sources

• University of Minnesota Extension: Grazing Horses Prone to Laminitis
• Merck Veterinary Manual: Laminitis in Horses
• The Horse: Current EMS and PPID Testing Recommendations
• University of Minnesota Extension: Caring for the Overweight Horse