Do Horses Need a Low-Carb Diet?

Do Horses Need a Low-Carb Diet?

By Dr Duncan Houston

“Low-carb” can be a useful phrase in horse nutrition, but it can also be misleading.

Horses are designed to eat carbohydrates. Grass, hay, pasture, beet pulp, hay cubes, and forage all contain carbohydrate in some form. The issue is not that carbohydrates are bad. The issue is which carbohydrates, how much, how quickly they are digested, and whether the horse can handle the insulin response.

For a fit horse in work, some starch and sugar may be tolerated well. For an overweight pony with a cresty neck, insulin dysregulation, or a history of laminitis, the same feed or pasture access can be dangerous.

The goal is not a no-carb diet.

The goal is controlled non-structural carbohydrate intake, safe forage, appropriate calories, and a feeding plan built around the horse in front of you.

Quick Answer

Some horses need a low-NSC diet, especially horses with equine metabolic syndrome, insulin dysregulation, obesity, PPID with high insulin, or a history of laminitis. NSC means non-structural carbohydrates, mainly sugars and starches, which can trigger high insulin responses in susceptible horses. EMS is associated with inappropriate insulin regulation, regional fat deposits, difficulty losing weight, and a high risk of laminitis. (ceh.vetmed.ucdavis.edu)

For horses with EMS, the core plan is usually tested low-NSC hay, controlled calories, reduced or eliminated pasture access, no grain or sweet feed, a ration balancer if needed, regular farrier care, and exercise only when the horse is sound. Merck states that diet is the most important part of EMS management and recommends low-NSC hay, elimination of grazing, grains, and treats for EMS patients. (Merck Veterinary Manual)

What Does “Low-Carb” Mean for Horses?

In horse nutrition, “low-carb” usually does not mean removing all carbohydrate.

It usually means reducing the rapidly digested carbohydrates that drive higher insulin responses. These are called non-structural carbohydrates, or NSC.

NSC includes:

• Simple sugars

• Starches

• Fructans, depending on the lab method and forage type

• Other water-soluble or ethanol-soluble carbohydrate fractions

Structural carbohydrates are different. These include fibre components such as cellulose and hemicellulose. They are fermented more slowly by hindgut microbes and are a normal, essential part of a horse’s diet.

So when people say a horse needs a “low-carb diet,” the better phrase is usually:

This horse needs a low-NSC, forage-based diet.

That is a very different thing from trying to remove fibre.

Why Carbohydrate Type Matters

The horse’s digestive system is built around forage.

Fibre is fermented in the hindgut and provides energy steadily. Sugar and starch are digested more rapidly and can create a stronger insulin response. In healthy horses, that may be managed normally. In insulin-dysregulated horses, the response can be exaggerated and prolonged.

UC Davis explains that when EMS horses eat meals high in certain carbohydrates, they produce higher than normal insulin levels and are slow to return to baseline. These horses are at high risk for laminitis, especially with pasture or high-carbohydrate feeds. (ceh.vetmed.ucdavis.edu)

That is the reason low-NSC feeding matters.

It is not diet fashion. It is hoof protection.

What Is Equine Metabolic Syndrome?

Equine metabolic syndrome, or EMS, is a metabolic disorder associated with insulin dysregulation, abnormal fat storage, and high laminitis risk.

Common warning signs include:

• Easy weight gain

• A cresty neck

• Fat pads around the tailhead, shoulders, sheath, udder, ribs, or behind the shoulders

• Difficulty losing weight

• Foot soreness after pasture access

• Recurrent laminitis

• Hoof rings

• High insulin on blood testing

• A “lives on air” type horse or pony

UC Davis notes that EMS commonly affects thrifty equids such as ponies, donkeys, Arabians, and mustangs, although any horse can be affected. (ceh.vetmed.ucdavis.edu)

Not every overweight horse has EMS. Not every EMS horse is massively overweight. That is why testing matters.

Why Low-NSC Diets Matter for Laminitis Prevention

Laminitis is one of the biggest reasons veterinarians care about insulin and NSC.

High insulin is strongly linked to endocrinopathic laminitis. Merck describes endocrine dysfunction as probably the most common underlying cause of laminitis in horses today, with hyperinsulinaemia considered the predisposing condition. (Merck Veterinary Manual)

Laminitis damages the sensitive tissues that suspend the coffin bone inside the hoof. Severe cases can lead to rotation or sinking of the coffin bone and may become life-threatening. Merck describes laminitis as one of the most important and catastrophic diseases in horses. (Merck Veterinary Manual)

This is why the diet needs to change before the horse is crippled.

A cresty, overweight, pasture-sensitive horse is not just “a good doer.” That horse may be standing at the edge of a hoof crisis.

Are Grain and Sweet Feed the Main Problem?

Sometimes, yes.

Grain, sweet feed, molasses-heavy feeds, and high-starch concentrates can be a major problem in metabolic horses. But they are not the only problem.

Pasture is often the bigger issue.

A horse may receive no grain at all and still be at serious laminitis risk if they are eating lush, high-sugar grass. UC Davis specifically notes that EMS horses are at high risk for laminitis when given access to pasture or high-carbohydrate feeds. (ceh.vetmed.ucdavis.edu)

Cornell’s equine obesity and EMS guidance is blunt: if a horse is not exercising, it does not need grain and should be fed hay, with hay weighed carefully. It also recommends grass hay with NSC below 10% for EMS horses and warns that grass sugar content varies. (Cornell Vet College)

So the common myth is:

“My horse does not get grain, so the diet is safe.”

The reality is:

Pasture and hay can still be too high in sugar and starch for the wrong horse.

What NSC Level Is Safe?

For EMS horses, the commonly used target is hay below 10% NSC on a dry matter basis.

Merck recommends low non-structural carbohydrate hay at 10%, determined by feed analysis, for EMS patients. (Merck Veterinary Manual)

UC Davis also recommends that hay for EMS horses ideally be below 10% NSC on a dry matter basis. (ceh.vetmed.ucdavis.edu)

This is why hay testing is so useful. Looking at hay does not reliably tell you the NSC level.

Do not assume:

• Grass hay is always safe

• Alfalfa is always unsafe

• Mature hay is always low sugar

• Pale hay is safe

• Green hay is too rich

• Soaking always fixes the problem

The lab test beats the guess.

Can Hay Soaking Help?

Yes, sometimes.

Soaking hay can reduce some water-soluble carbohydrates, but the effect is variable. Merck lists soaking hay for 60 minutes as one strategy to decrease NSC content in EMS management. (Merck Veterinary Manual)

Cornell notes that soaking hay for 30 minutes before feeding can reduce water-soluble carbohydrates, but the safer message is still to test hay where possible. (Cornell Vet College)

Important points:

• Soaking does not reliably turn unsuitable hay into safe hay.

• Soaking can leach minerals, so the mineral plan may need adjustment.

• Soaked hay should not sit around and spoil.

• In cold weather, soaked hay can freeze.

• In hot weather, soaked hay can ferment.

Soaking is a tool, not a guarantee.

Is Alfalfa Safe for Metabolic Horses?

Sometimes.

Alfalfa is often lower in sugar and starch than people assume, but it is also higher in protein, calcium, and calories than many grass hays. It may be useful for some horses and inappropriate for others.

For metabolic horses, the decision should be based on:

• NSC level

• Total calories

• Body condition

• Laminitis history

• Protein needs

• Calcium and phosphorus balance

• Whether the horse needs weight loss or weight gain

The problem is not the name of the hay. The problem is the full nutrient profile and the horse’s risk.

A test result beats stable-yard folklore every time.

Risk Framework: How Worried Should You Be?

Low Risk

This is usually lower risk if your horse:

• Has ideal body condition

• Has no cresty neck

• Has no fat pads

• Has no laminitis history

• Has normal insulin testing

• Exercises regularly and is sound

• Eats mostly appropriate forage

• Does not receive unnecessary grain or sweet feed

This horse may not need a strict low-NSC plan, but forage-first feeding and body condition monitoring still matter.

Moderate Risk

This is more concerning if your horse:

• Is an easy keeper

• Has mild fat pads

• Has a slight crest

• Gains weight on pasture

• Gets grain despite low workload

• Has not had hay tested

• Has not had insulin checked

• Becomes slightly pottery after grass

This is the stage where prevention should start. Do not wait for laminitis to prove the point.

High Risk

This is high risk if your horse:

• Is overweight or obese

• Has a firm cresty neck

• Has regional fat deposits

• Has confirmed insulin dysregulation

• Has EMS

• Has PPID with high insulin

• Has had laminitis before

• Becomes footsore after pasture

• Is still eating pasture, grain, molasses, or untested hay

This horse needs a veterinary-guided metabolic diet and hoof plan.

Critical

This is urgent if your horse:

• Is suddenly lame

• Is reluctant to walk

• Rocks back onto the hindlimbs

• Has heat in the hooves

• Has strong or bounding digital pulses

• Lies down more than normal

• Refuses to turn

• Has known EMS or PPID and any new foot soreness

This is not a feed adjustment for next week. This is possible laminitis and needs veterinary care.

When Is This an Emergency?

Call your vet urgently if your horse has signs of laminitis.

Red flags include:

• Short, pottery steps

• Reluctance to walk on hard ground

• Reluctance to turn

• Heat in the hooves

• Strong digital pulses

• Rocked-back stance

• Repeated lying down

• Refusal to pick up one foot because the others hurt

• Sudden lameness after pasture access

• Known EMS or PPID with any new foot soreness

UC Davis lists increased digital pulses, increased hoof temperature, weight shifting, lameness, an uncomfortable stance, unwillingness to move, and reluctance to rise as signs of acute laminitis. (ceh.vetmed.ucdavis.edu)

Do not exercise a horse with active laminitis. Do not turn them out on grass to “loosen up.” Do not wait a few days to see whether it settles.

The feet need urgent protection.

What Else Can Look Like a Carb Problem?

Not every overweight, footsore, or dull horse has the same issue.

Important rule-outs include:

• Equine metabolic syndrome

• PPID

• Insulin dysregulation

• Obesity without confirmed EMS

• Overfeeding calories

• High-NSC pasture

• High-NSC hay

• Grain or sweet feed

• Hoof abscess

• Poor farriery

• Arthritis or chronic pain limiting movement

• Dental disease affecting diet

• Poor exercise tolerance

• Hidden treats or multiple people feeding

• Pregnancy

• Medication effects

• Chronic laminitis

• Supporting-limb pain from another injury

Cornell notes that EMS and PPID can occur together, so middle-aged or older horses with laminitis and insulin resistance may need testing for both disorders. (Cornell Vet College)

This is why the best plan is not just “remove carbs.”

It is diagnose the risk, then feed accordingly.

How Is Insulin Dysregulation Tested?

Testing depends on the horse, the vet, and the clinical picture.

Common tests include:

• Resting insulin

• Resting glucose

• Oral sugar test

• Oral glucose test

• Leptin in some cases

• ACTH testing if PPID is possible

Cornell lists insulin, the oral sugar test, and leptin as recommended tests for EMS diagnosis and follow-up. It also notes that EMS and PPID can be seen separately or together. (Cornell Vet College)

Michigan State University notes that the oral sugar test is more sensitive than resting insulin and glucose for assessing insulin and glucose metabolism. (MSU Veterinary Medicine)

A normal resting insulin does not always end the conversation if the horse looks metabolically suspicious. Your vet may recommend dynamic testing.

What Should You Do Next?

1. Remove the Obvious Sugar and Starch Sources

For high-risk horses, remove or avoid:

• Sweet feed

• Grain mixes

• Molasses

• High-starch concentrates

• Large carrot or apple treats

• Sugary commercial treats

• Unrestricted pasture

• Unlabelled feeds

• “Conditioning” feeds unless they are genuinely low-NSC and appropriate

The feed bucket should become boring. Boring is good. Boring protects hooves.

2. Test the Hay

If your horse has EMS, laminitis history, insulin dysregulation, obesity, a cresty neck, or pasture sensitivity, test the hay.

Ask for values including:

• Dry matter

• ESC

• WSC

• Starch

• NSC, if reported

• Digestible energy

• Protein

• Minerals

For high-risk horses, target hay below 10% NSC on a dry matter basis where possible. (Merck Veterinary Manual)

3. Weigh the Forage

Do not feed by flakes.

For EMS horses at ideal body condition, Merck recommends low-NSC hay divided into multiple small meals or slow feeders, with a daily total of 2% of body weight when body condition score is 5 out of 9. In obese horses, the daily total can be reduced to 1.5% of body weight, but severe restriction can be harmful and increase hyperlipemia risk. (Merck Veterinary Manual)

If using an ideal weight target, work with your vet so the horse loses weight safely.

4. Control Pasture

Pasture is often the biggest risk.

Options include:

• Dry lot turnout

• Track system

• Grazing muzzle

• Strip grazing

• Very limited supervised turnout

• No pasture during high-risk periods

• Tested low-NSC hay instead of grass

Merck notes that pasture nutrient composition can change from hour to hour, and decisions about grazing in EMS horses should depend on clinical signs, body condition, and post-meal insulin response. (Merck Veterinary Manual)

For high-risk horses, “just a little grass” can still be too much.

5. Use a Ration Balancer if Needed

A low-NSC hay-only diet may not provide enough minerals, vitamin E, salt, selenium, copper, zinc, or amino acids.

Many metabolic horses do not need grain. They need a low-calorie ration balancer or mineral supplement that fills nutrient gaps without adding sugar, starch, or unnecessary calories.

Merck recommends a low-sugar ration balancer as one dietary strategy in EMS management. (Merck Veterinary Manual)

6. Exercise Only When the Horse Is Sound

Exercise can improve insulin regulation and weight loss, but only after laminitis has resolved.

Merck notes that once laminitis has resolved, exercise helps improve insulin sensitivity by building muscle and reducing fat, but it is essential that increasing exercise does not make the horse lame. (Merck Veterinary Manual)

If the horse is footsore, do not work them.

The feet come first.

7. Involve the Farrier Early

EMS is not only a diet problem. It is a hoof-risk problem.

Merck states that skilled farriery is essential in all EMS cases, even without obvious acute laminitis, and recommends regular trimming in at-risk horses. (Merck Veterinary Manual)

Hoof radiographs may be useful if there is laminitis history, hoof rings, chronic soreness, or suspected coffin bone movement.

What About Supplements?

Be careful.

Magnesium, chromium, cinnamon, omega-3s, and other supplements are often marketed for insulin sensitivity. Some may have roles in specific horses, especially if there is a documented deficiency or another reason to use them. But they are not the foundation of EMS management.

Merck states that supplements including cinnamon, chromium, and magnesium have been suggested to improve insulin regulation, but none have been shown to do so in horses in experimental situations. (Merck Veterinary Manual)

This is the hierarchy:

1. Diet

2. Pasture control

3. Weight management

4. Hoof care

5. Exercise when sound

6. Testing and monitoring

7. Supplements only if they make sense

Do not let a supplement distract from hay and grass control.

That is expensive hoof roulette.

Common Mistakes Owners Make

Thinking “Low-Carb” Means No Fibre

Fibre is essential. The goal is lower sugar and starch, not removing forage.

Removing Grain but Leaving Pasture Uncontrolled

For many metabolic horses, grass is the real problem.

Not Testing Hay

Hay can look safe and still be too high in NSC.

Starving the Horse

EMS horses need controlled calories, not crash dieting. Severe restriction can be dangerous.

Exercising a Laminitic Horse

Exercise helps only when the horse is sound. Active laminitis needs rest, pain control, hoof support, and veterinary care.

Trusting Supplement Marketing

No supplement can outwork lush grass, high-NSC hay, grain, and excess calories.

Forgetting PPID in Older Horses

Older horses with insulin problems, laminitis, coat changes, topline loss, or increased drinking and urination may need PPID testing as well.

How To Prevent Diet-Related Laminitis

Prevention is much easier than treating a painful laminitis case.

Focus on:

• Body condition scoring every 2 to 4 weeks

• Monitoring the neck crest and fat pads

• Testing insulin in high-risk horses

• Testing ACTH in older horses or PPID suspects

• Feeding tested low-NSC hay

• Weighing forage

• Restricting pasture

• Avoiding grain, sweet feed, molasses, and sugary treats

• Using a ration balancer instead of calorie-heavy feed

• Keeping water and salt available

• Scheduling regular farrier care

• Checking digital pulses in high-risk horses

• Exercising only when sound

• Adjusting the plan before spring and autumn pasture risk

The best metabolic plan is boring, consistent, and measured.

Very dull. Very effective.

Will My Horse Be Okay?

Many horses with EMS or insulin dysregulation do well when the problem is recognised early and managed properly.

The outlook is better when:

• Laminitis has not occurred yet

• Insulin can be controlled

• Pasture can be restricted

• Hay can be tested

• Body weight improves slowly

• Farriery is consistent

• The horse can exercise safely

The outlook is more guarded if the horse has repeated laminitis, coffin bone rotation, severe obesity, uncontrolled insulin, PPID, or ongoing pasture access.

The key is early action.

A cresty neck is not cosmetic. Foot soreness after grass is not normal. A horse that “lives on air” may still be eating too much sugar and starch for their metabolism.

FAQs

Do all horses need a low-carb diet?

No. Healthy horses in appropriate body condition and regular work may not need strict low-NSC feeding. Low-NSC diets are most important for horses with EMS, insulin dysregulation, obesity, PPID with high insulin, or laminitis risk.

What is the best hay for a metabolic horse?

The best hay is clean, mould-free, lower calorie where weight loss is needed, and tested below 10% NSC on a dry matter basis if possible. Merck recommends low-NSC hay at 10% for EMS management. (Merck Veterinary Manual)

Can metabolic horses eat pasture?

Some high-risk horses should have pasture eliminated, especially during active laminitis or weight loss. Others may later tolerate limited, muzzled, carefully monitored turnout. The decision should be based on insulin status, body condition, hoof history, and veterinary advice.

Does soaking hay make it safe?

Soaking can reduce some water-soluble carbohydrates, but the reduction is variable. It may help when hay is borderline, but it does not replace testing or a full metabolic plan.

Should I give magnesium or chromium for EMS?

Do not rely on them. Merck notes that magnesium, chromium, cinnamon, and similar supplements have not been shown to improve insulin regulation in horses in experimental settings. Diet and pasture control matter far more. (Merck Veterinary Manual)

Final Thoughts

Low-carb diets for horses are often misunderstood.

Horses need carbohydrate. They need fibre. They need forage. What some horses cannot safely handle is excess sugar and starch, especially if they have EMS, insulin dysregulation, obesity, PPID, or laminitis risk.

The safest plan is not “no carbs.”

It is tested low-NSC forage, controlled calories, restricted pasture, no unnecessary grain, a balanced mineral plan, regular farrier care, and exercise only when the horse is sound.

The horse does not need a trendy diet.

They need a diet their insulin and hooves can survive.

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If you are unsure whether your horse needs a low-NSC diet, hay testing, pasture restriction, insulin testing, or urgent laminitis care, ASK A VET™ can help you work through the risk signs and decide what needs veterinary attention.