Insulin Dysregulation in Horses: Why Fit Sport Horses Can Have It Too

Can a fit sport horse have insulin dysregulation?

Yes. Insulin dysregulation in horses is not just a problem of fat ponies: a North Carolina State University study found it in 22.8% of 180 sport horses, and how the horses looked did not predict who had it. EquiManagement reported the findings on Oct. 5, 2026, and they matter right now, as fall grass puts at-risk horses on the edge of laminitis.

What the NC State team found

The study, led by Kimberly Hallowell, DVM, with Lauren Schnabel's group at NC State's College of Veterinary Medicine, was published in the Equine Veterinary Journal in 2026. Here are the headline numbers:

• Who: 180 sport horses, at least 2 years old, with no known history of equine metabolic syndrome or laminitis. 140 came in for orthopedic (lameness) evaluation at the university hospital; 40 were tested at local farms.
• How: each horse had an oral sugar test, a vet-run challenge that measures how much insulin the body releases after a set dose of sugar.
• Result: 41 horses (22.8%) had insulin dysregulation.
• The surprise: only 11 of those 41 (26.8%) had high fasting insulin. The other 30 were found only because the sugar challenge was done.
• Looks didn't help: 60.5% of the horses were overweight, yet neither body condition score nor cresty-neck score predicted ID.
• One predictor: in males only, a higher ratio of two fat-tissue hormones (leptin to adiponectin) was linked to ID. It didn't hold for mares.

In the authors' words, vets can't rely on a horse's appearance to make decisions about ID.

The stall-side test

The team also compared a quick stall-side insulin test with a validated lab assay. They agreed well (correlation r = 0.81), and the quick test was excellent at sorting horses into ID or not ID. But it read higher on average, by about 13.6 µIU/mL, and varied more at high insulin levels.

For owners, the takeaway is simple. A stall-side result can be useful, but your vet needs to know which test was used, because the numbers aren't interchangeable.

What insulin dysregulation is, in plain language

Insulin is the hormone that clears sugar from the blood after a meal. In a horse with ID, the body overreacts and pumps out far too much insulin, either all the time or only after a sugary or starchy meal. You may also hear the related, older term insulin resistance.

ID is the core feature of equine metabolic syndrome (EMS). The Merck/MSD Veterinary Manual describes EMS as ID plus a raised risk of laminitis, often with obesity or fat pads, though lean versions exist.

Risk is higher in some types. MSD lists ponies, Saddlebreds, Tennessee Walking Horses, Paso Finos, Morgans and Mustangs, usually between about 5 and 16 years old. But the NC State study is a reminder that sport horses in regular work are not exempt.

Why ID matters: the link to laminitis

High insulin can damage the laminae, the tissue that holds the coffin bone inside the hoof. This is called hyperinsulinemia-associated or endocrinopathic laminitis. MSD estimates it accounts for about 90% of laminitis cases in horses.

Laminitis doesn't always arrive as a dramatic founder. It can start quietly, as a horse that's a little short-strided on hard ground or "just not right." In an earlier 2025 report on this same project, Hallowell said nearly half of the first 100 horses showed at least one X-ray sign linked to laminitis, a preliminary finding the team was still studying.

That's why ID belongs on the radar of anyone with a horse in work, not just owners of chubby ponies. For the full picture on hoof warning signs, read Fall Laminitis in Horses.

Why fall pasture matters now

Cool-season grasses, which grow in spring and fall, carry more sugar and starch (NSC) than warm-season grasses, according to University of Georgia Extension. A horse with ID that grazes lush fall regrowth can get a big insulin spike day after day.

Practical ideas to discuss with your vet:

• Limit grass: dry lot, a track system or strip grazing.
• A grazing muzzle: a small Kentucky study found muzzles roughly halved the insulin peak after grazing. See Grazing Muzzle for Horses: Do They Lower Insulin?.
• Test your hay: UGA suggests keeping NSC near 10% of the diet for horses with ID. A forage analysis shows what's actually in your hay.
• Don't muzzle part-time and assume it works: UGA notes horses often make up for it by eating more when the muzzle comes off.

Our nutrition section covers forage basics.

Insulin resistance horse signs: when to call the vet

There is no reliable way to spot ID by eye, as the study shows. Still, these signs should start a conversation with your vet:

• Subtle lameness or footsoreness, especially on hard or stony ground, or after time on grass.
• A history of laminitis, even one mild episode.
• Regional fat: a cresty neck, fat pads behind the shoulders, around the tailhead or above the eyes, or fat around the sheath or udder.
• A horse that won't lose weight despite a sensible diet and work.
• Unusual growth rings on the hooves, which can point to past bouts of laminitis.
• Drinking and urinating more than usual, a sign the British Horse Society lists.
• Breed or type at higher risk, or an easy keeper.

Call the vet right away, not at the next routine visit, if your horse is reluctant to walk, rocks back off the front feet, has hot feet or a strong pulse at the hoof. Those are laminitis warning signs. Our health basics page explains how to check digital pulses.

Use our body condition score guide to track weight. Just remember: in this study, a good score didn't rule out ID.

Why a fasting test alone can miss cases

A single resting (fasting) insulin test is easy, but it only catches horses whose insulin is high all the time. Many horses with ID look normal at rest and only overreact after a sugar load. MSD makes the same point: some horses are normal in every way except how they handle oral sugar.

That's exactly what the NC State team saw: nearly three-quarters of the ID horses would have been missed by a fasting result alone. A dynamic test, such as the oral sugar test, adds a controlled sugar challenge.

This is a vet-run test. Timing, preparation and interpretation matter, and the BHS notes that travel alone can raise insulin. Don't try to run it yourself; ask your vet whether it fits your horse.

What to do next: a vet checklist

Take these questions to your next appointment, ideally before the fall flush:

1. Should my horse be tested for ID, and would a dynamic test make more sense than resting insulin?
2. If we already tested, which method was used, and should we retest?
3. Was the result from a stall-side test or a lab, and how should I compare future numbers?
4. Does my horse's lameness, hoof shape or past soreness raise your concern?
5. Would hoof X-rays help?
6. How much grass is safe this fall: dry lot, muzzle or limited hours?
7. Should I test my hay?
8. How should exercise fit in, given my horse's feet?
9. Which signs mean I should call you the same day?

Costs and timelines depend on your vet and lab, so ask for a quote.

What to watch next

This is one hospital population, and many of the horses came in for lameness work, so the real rate in all sport horses may differ. Watch for follow-up papers from the NC State group on hoof X-ray findings and on how the stall-side test performs in the field.

Meanwhile, the message is clear: you can't judge insulin by looks. If your athlete fits any of the risk signs above, talk to your vet. More guides live in Trends.