Insulin Resistance in Horses: Why High Insulin Leads to Laminitis

Insulin resistance in horses is one of the most common — and most dangerous — metabolic conditions veterinarians see today. When insulin levels stay too high for too long, the risk of laminitis increases dramatically. The challenge is that insulin resistance often develops quietly, with few obvious signs until a crisis occurs. Understanding what insulin resistance really is — and catching it early — can prevent devastating hoof damage and protect a horse’s long-term soundness.

At Countryside Equine Hospital, insulin resistance is one of the conditions veterinarians work hardest to identify before laminitis ever appears.

What Is Insulin Resistance in Horses?

Insulin resistance occurs when a horse’s cells no longer respond properly to insulin, the hormone responsible for moving glucose from the bloodstream into tissues for energy.

In a healthy horse:

Glucose rises after eating
Insulin is released
Cells respond appropriately
Blood sugar returns to normal

In an insulin-resistant horse:

Glucose stays elevated
The body produces more insulin
Cells stop responding efficiently
Insulin levels remain dangerously high

This chronic elevation — not just glucose — is what places the horse at high risk for laminitis.

Why High Insulin Causes Laminitis

Insulin has direct effects on blood flow and tissue integrity within the hoof. When insulin remains elevated, it disrupts the delicate structures that suspend the coffin bone inside the hoof capsule.

The result:

Weakened laminar attachments
Reduced blood flow
Inflammation within the hoof
Structural failure over time

This is why insulin resistance is one of the strongest predictors of laminitis, even in horses that have never had hoof problems before.

“I can’t tell you how many times we find some form of metabolic disease behind a laminitis case. If we could catch the insulin resistance earlier, we could prevent so much of the damage we end up seeing.”
— Dr. Dan Carter, Countryside Equine Hospital

What Insulin Resistance Looks Like (and Why It’s Misleading)

One of the biggest misconceptions about insulin resistance is that it only affects overweight horses.

In reality, IR can look very different from horse to horse.

Some horses with IR are:

Overweight with obvious fat deposits
Easy keepers that gain weight easily
“Cresty-necked” or thick through the tailhead

Others may:

Appear thin or ribby
Store fat internally rather than externally
Show few outward signs until laminitis develops

Certain breeds also have a genetic predisposition, including many gaited breeds and ponies, which can store fat internally rather than visibly.

Early Warning Signs of Insulin Resistance

Because insulin resistance doesn’t always show obvious physical changes, early clues are often subtle.

Watch for:

Difficulty maintaining a healthy weight
Fat pads behind the shoulders, tailhead, or crest
Sudden hoof sensitivity
Recurrent foot soreness without clear cause
Abnormal response to steroids

At Countryside, insulin testing is often recommended before administering steroid medications, as steroids can dramatically increase insulin levels and trigger laminitis in at-risk horses.

Stall-Side Testing: Why Speed Matters

Traditional insulin testing often required sending samples to outside laboratories, with results taking days to return.

Today, stall-side insulin testing allows veterinarians to:

Measure insulin levels in 15 minutes
Make immediate decisions
Avoid dangerous treatments when insulin is high

This is especially important when:

A horse is about to receive joint injections
Laminitis is suspected
Rapid intervention could prevent a crisis

Knowing insulin levels now — not days later — can make all the difference.

Medication vs Lifestyle: Why Both Matter

When insulin levels are dangerously high, medication is often necessary to reduce immediate risk.

Common medical options may include:

Metformin
Newer glucose-regulating medications

However, medication alone is not a long-term solution.

Without addressing diet and exercise, horses can:

Become resistant to medication
Require increasing doses
Remain at risk for laminitis

Lifestyle management is essential for lasting improvement.

The Role of Diet in Managing Insulin Resistance

Dietary management focuses on reducing simple sugars and starches while maintaining proper nutrition.

Key principles include:

Forage-based diets
Low-NSC feeds
Ration balancers instead of traditional grain
Avoiding high-sugar hays and grasses

Hay testing — rather than guessing — allows owners and veterinarians to make informed feeding decisions. When necessary, soaking hay can further reduce sugar content.

Why Exercise Is One of the Most Powerful Tools

Exercise is one of the fastest ways to reduce insulin levels.

Physiologically:

Initial activity burns blood glucose
Continued exercise burns stored glycogen
Longer sessions mobilize fat stores

This is why veterinarians often recommend:

At least 30 minutes of exercise
Four or more days per week
Long trotting or brisk walking

Early detection matters — once laminitis develops, exercise may no longer be safe.

When Insulin Resistance Overlaps With Other Conditions

Insulin resistance frequently overlaps with:

Equine Metabolic Syndrome (EMS)
Cushing’s disease (PPID)

If a horse tests positive for one metabolic condition, comprehensive testing for the others is often recommended. These conditions tend to “travel together,” and treating only one can leave another unaddressed.

When Should a Horse Be Tested for Insulin Resistance?

Testing should be considered when:

A horse gains weight easily
Fat deposits appear
Steroids are being considered
Hoof changes occur without explanation
A horse is over 10–12 years old
Laminitis has occurred previously

Metabolic diseases can occur anytime throughout the year. Spring is an especially important time to test due to seasonal changes in metabolism and an increase in pasture sugars.

Prevention Is Always Easier Than Repair

Laminitis caused by insulin resistance can be life-altering. Despite careful management, affected horses may still experience laminitic flares.

Early testing allows veterinarians to:

Adjust management before severe damage occurs
Avoid risky medications
Implement diet and exercise plans early
Protect hoof integrity long-term

At Countryside, we focus on accurate diagnosis and preventive care— addressing issues before they progress, not after.

Commonly Asked Questions

What is insulin resistance in horses?
Insulin resistance occurs when a horse’s cells no longer respond properly to insulin, causing insulin levels to remain elevated and increasing the risk of laminitis.

Why does high insulin cause laminitis?
Chronically high insulin disrupts blood flow and tissue integrity in the hoof, weakening the laminae and increasing the risk of structural failure.

Can thin horses have insulin resistance?
Yes. Some horses store fat internally and may appear thin while still having dangerously high insulin levels.

How is insulin resistance diagnosed?
Insulin resistance is diagnosed through blood testing, including stall-side insulin tests that provide rapid results.

Can insulin resistance be reversed?
In many cases, insulin levels can be significantly improved through diet changes, exercise, and targeted medical management.

If you found this article helpful and want to experience compassionate, diagnostically-driven equine care, Countryside Equine Hospital is the place for you. Locally owned and privately operated, we’ve been proudly serving our local community since 1991. With integrity at the heart of our care, we deliver progressive medicine and exceptional service

Do you have an equine medical question or concern? We’re here for your horse day and night, offering 24/7/365 emergency care when it matters most. Give us a call at (770) 787‑4711 or visit us at 3395 Maughon Road, Covington, GA  30014. You can also learn more and request an appointment on our website at countrysideeq.com.

Published By

Dr. Rachel Akin