Fall Laminitis in Horses: Why Autumn Grass Can Founder Your Horse

Fall laminitis in horses: why autumn grass can be risky

Fall laminitis in horses happens when grass that looks tired and half-dormant is actually loaded with sugar, and a sensitive horse's insulin spikes after eating it. Sunny autumn days let grass keep making sugar, while cold nights below about 40°F (4°C) stop the plant from burning it off, so levels stay high into the next day.

The question is timely. The Horse is hosting a free webcast, Understanding Laminitis in Horses, on Thursday, Sept. 24, 2026, at 8 p.m. EDT, where Ohio State University internal medicine specialist Dr. Teresa Burns will cover warning signs, risk factors and prevention.

Laminitis is inflammation and damage in the laminae, the tissue that bonds the coffin bone to the hoof wall; "founder" is the barn word for it, usually once the bone has shifted. It is painful, tends to come back and is far easier to prevent than to fix. Our anatomy guide shows how the hoof is built.

Why fall grass gets so sugary

Grass makes sugar during the day and spends some of it overnight to grow. In fall, that balance tips toward storage:

• Sunny days keep sugar production high.
• Cold nights slow the plant down, so it holds on to sugar instead of using it. University of Minnesota (UMN) Extension notes that grass collects sugar when temperatures drop below 40°F.
• Frost can lock sugars in the plant for more than a week, per UMN Extension.
• Stress from drought or overgrazing pushes sugar higher, and most forage grasses store it in the bottom 3 to 4 inches, right where a horse on a short pasture is grazing.

What are fructans?

Cool-season grasses such as fescue, orchardgrass, ryegrass, bluegrass, timothy and brome store extra energy as fructans. Horses can't digest fructans in the small intestine, so they ferment in the hindgut. Fructans, simple sugars and starch together make up a forage's nonstructural carbohydrates, or NSC.

Here is the update many older articles miss. The Equine Endocrinology Group (EEG), an international panel of specialists, says more than 90% of laminitis cases are hyperinsulinemia-associated laminitis, triggered by high insulin, and that NSC is the main driver of insulin release. For a sensitive horse, the goal is simple: keep total grass sugar low.

Can fall grass cause founder?

Yes, in susceptible horses. Risk depends on the weather, the pasture and, above all, the horse.

Which horses are most at risk

Most horses handle fall grass fine. The ones to worry about:

• Horses with equine metabolic syndrome (EMS) or insulin dysregulation, often easy keepers with a cresty neck or fat pads near the tail.
• Overweight horses of any breed. Score body condition monthly on the 1-to-9 Henneke scale and track weight with a tape.
• Ponies, miniature horses and donkeys, which tend to be easy keepers.
• Any horse that has had laminitis before, because it often recurs.
• Older horses with PPID, also called equine Cushing's disease.

Cushing's disease in horses: why fall matters

PPID is a slow, age-related disease that affects the pituitary gland. The EEG estimates it affects about 20% of equids over 15. Affected horses overproduce ACTH, a stress-related hormone.

Every horse's ACTH naturally rises in late summer and fall. In PPID horses that rise can be exaggerated, and about 30% of horses with PPID also have insulin dysregulation, a combination that raises laminitis risk.

Early signs, listed by the EEG, are easy to miss:

• Patches of long hair or a coat that sheds late.
• Some loss of topline muscle along the back.
• Being duller or less willing to work.
• Sweating more or less than usual.

The EEG also lists laminitis linked to high insulin as a possible complication, so an unexplained bout in an older horse is worth raising with your vet.

Ask your vet about PPID testing in fall if your horse is older and shows any of these signs; the EEG does not recommend testing horses with no signs. Fall testing is fine: the guidelines use season-specific ranges with higher cutoffs from late summer through autumn, and retesting in the same season each year keeps results comparable. Treatment, dosing and follow-up are decisions for your veterinarian.

One more nuance: not every Cushing's horse needs a strict low-sugar diet. The EEG notes many PPID horses are lean and need more calories; carbohydrate restriction is for those that also test positive for insulin dysregulation.

A fall grazing plan that lowers the risk

1. Know your horse's risk. Ask your vet whether an insulin test makes sense, especially for easy keepers and horses over 10.
2. Watch the forecast. Nights below 40°F followed by sunny days are the classic setup, so tighten grazing then.
3. Graze early. UMN Extension points to roughly 3 a.m. to 10 a.m. as the lower-sugar window. After a frosty night, morning grass stays high too.
4. Wait out the frost. UMN Extension recommends waiting up to a week after a killing frost before turning horses back out. Oregon State University Extension is stricter for laminitis-prone horses: keep them off pasture for several weeks after the first fall freeze. Ask your vet which fits your horse.
5. Skip short, stressed pasture. Don't let a metabolic horse mow down an overgrazed field or graze seed heads, which are also high in carbohydrates.
6. Use a dry lot. A small paddock with little or no grass, hay and a companion is the EEG's starting point for obese metabolic horses.
7. Keep sound horses moving. The EEG says any exercise helps weight loss and insulin sensitivity unless laminitis is present. Ask your vet first if your horse has ever had it.

Grazing muzzles for laminitis that don't rub

A muzzle lets a horse stay out with the herd while eating less grass. A University of Minnesota study found muzzles cut grass intake by about 30%, and UK research in ponies measured reductions as large as 85%.

Rubs are the top complaint, and they are usually a fit problem:

• Two-finger gap. You should fit two fingers between the muzzle and the face all the way around.
• Rubs mean a bad fit. A muzzle that rubs is usually too small. Pad pressure points with fleece or sheepskin, and check the nose, chin and cheeks daily.
• Breakaway safety. Choose a breakaway crownpiece or safety halter so a snagged horse can get free.
• Time limit. Keep wear to about 10 to 12 hours a day, then use a stall or dry lot with hay.
• Go slow. Most horses adjust within about a week when the muzzle is introduced gradually.
• Test the water. Make sure your trough or automatic waterer works with the muzzle, and watch your horse drink before you leave.
• Watch the teeth. Some owners worry about front-tooth wear from grazing through the muzzle floor, so ask your vet or equine dentist to check incisors at routine visits.

A muzzle is not a free pass. On a high-risk day a muzzled horse still eats sugary grass, and a horse with active or recent laminitis should not graze until your vet says so.

Low-sugar hay for a metabolic horse

When grass is off the menu, hay is the whole diet, and you can't judge its sugar by eye.

• The target: the EEG recommends grass hay with NSC under 10% on a dry-matter basis. Some nutritionists use sugar (ESC) plus starch under 10% instead.
• Test it. Core-sample several bales of the same cutting and send them to a forage lab. Your county extension office can help.
• Soak if unsure. For untested hay or hay over 10%, the EEG advises soaking in cold water for at least 60 minutes. Dump the soaking water afterward, since the dissolved sugar stays in it.
• Don't starve the horse. Use slow feeders or small, frequent meals so your horse never goes long without forage. Crash diets can trigger hyperlipemia, a dangerous fat disorder, especially in ponies, minis and donkeys.
• Cut the extras. Skip grain and sugary treats, and ask about a low-sugar ration balancer for vitamins and minerals.

Your vet can set the right amount; our nutrition guide explains forage-first feeding.

Signs of laminitis and when to call the vet

The EEG notes laminitis can occur without obvious lameness. Watch for:

• Reluctance to walk, or short, careful steps, especially on turns or hard ground.
• The "sawhorse" stance: front feet stretched forward, weight rocked back.
• Shifting weight from foot to foot, or lying down more than usual.
• Warm hooves and a stronger, bounding digital pulse at the back of the fetlock.
• A pained, worried expression.

Laminitis is an emergency. Call your vet right away. While you wait, take the horse off grass, stand it on soft footing or deep bedding, don't force it to walk far, and give no medication unless your vet tells you to. Ask your vet to show you where to feel the digital pulse on a calm day, and see our health basics page for everyday checks.

What to do this week and what to watch next

• Sept. 24, 8 p.m. EDT: register free for The Horse's laminitis webcast with Dr. Teresa Burns.
• The first frost: check your local forecast and plan a dry lot for at-risk horses.
• Body condition: score and tape your horse now, then monthly through winter.
• Winter hay: test it as it arrives, before the whole supply is stacked.
• Hoof care: keep your farrier on schedule, and ask your vet whether X-rays make sense for a horse with a laminitis history.
• Older horses: ask about PPID and insulin testing if you've noticed a late-shedding coat or topline loss.

In the Southern Hemisphere the same risk arrives with autumn, roughly March to May. Everywhere, it returns with spring grass, so the habits you build now pay off all year.