Why Is My Horse Not Eating Grain? Common Causes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-02

A horse that refuses grain but still cleans up hay is telling you something. The most common reasons are mouth pain, stomach ulcers, a recent feed change, or a bad-tasting or spoiled batch. Because grain is a concentrated, high-starch meal, horses are often pickier about it than forage, so a horse not eating grain deserves a close look.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• Mouth pain is a leading cause. Sharp enamel points, loose or broken teeth, and lip wounds all make chewing hard grain uncomfortable [1].
• Gastric ulcers are common in performance horses and often show up as a horse that eats hay slowly but quits grain.
• A sudden feed change, a new bag, or a moldy or off-smelling batch can cause a flat refusal within a day.
• Sand accumulation in the gut can cause inappetence, especially in sandy or arid regions [2].
• If your horse also looks dull, has a fever, is pawing, or has not passed manure, call your veterinarian the same day.

What This Looks Like and What Is Normal

A healthy horse usually eats grain with enthusiasm. Normal grain intake can vary with age, workload, and feed type, but the pattern matters more than the amount. A horse that normally finishes a meal in ten minutes and now walks away after two bites is showing a real change.

Watch for these patterns:

• Slow eating. The horse takes a bite, drops grain, quids it, or holds the head sideways while chewing.
• Hay first, grain last. Some horses eat hay normally but leave grain untouched, which points toward a problem with the concentrated meal itself.
• Dropping feed. Grain falls from the mouth in clumps, called quidding.
• Bad attitude at feeding time. Ears back, head tossing, or backing away from the bucket.
• Weight loss over days to weeks. This follows reduced calorie intake.

Compare your horse to its own baseline. A horse that has always been a slow eater is different from one that changed overnight.

Why Is My Horse Not Eating Grain? Main Causes

Dental and Mouth Pain

The mouth is the first place to look. Wounds of the lips and cheeks are common in horses. They can come from a fall, a kick, an inappropriate bit, or a horse catching its lip or jaw while playing in a stall [1]. A lip laceration may come with a broken jaw or broken teeth, and wounds that penetrate into the mouth need more extensive treatment to avoid complications [1].

Dental disorders also matter for the stomach. Chewing roughage increases alkaline saliva production, which helps buffer stomach acid [3]. Horses with moderate to severe dental disease trended toward lower gastric pH in one study, meaning less natural acid buffering [3]. So a sore mouth can set up a cycle that irritates the stomach too.

Gastric Ulcers

Equine squamous gastric disease and equine glandular gastric disease both cause appetite changes. Gastric pH is a key factor in squamous disease, and low pH may also promote mucosal damage in glandular disease [3]. Omeprazole is currently recommended for both forms by the American and European colleges of veterinary internal medicine [3]. A horse with ulcers often eats hay but refuses grain, because grain stimulates more acid production.

Feed Changes and Palatability

Horses are creatures of habit. Switching brands, changing the amount, or introducing a new batch too fast can cause a refusal. Spoilage matters too. Musty, fermented, or moldy grain smells different, and horses often reject it before you notice the problem.

Forage quality also shifts. Forages differ widely in nutritional quality, and knowing the nutritive value helps you avoid underfeeding or overfeeding [4]. If your hay changed, your horse's overall ration may need adjusting, and that can affect how willing it is to eat grain.

Sand Accumulation

In sandy or arid areas, sand can build up in the gut. Sand enteropathy describes gastrointestinal disease from sand uptake and accumulation, and signs range from colic and fever to inappetence and poor performance [2]. Diagnosis based on signs alone is nearly impossible, and radiographic imaging is considered the gold standard [2]. In one study of desert horses, median sand depth was much greater in horses with sand colic (112.16 mm) than in other groups (10.5 mm and 12.0 mm), and every millimeter of sand raised the odds of sand colic by 2% [5].

Other Causes

• Pain elsewhere. Lameness, back pain, or a hoof abscess can dull appetite.
• Stress. Travel, a new herdmate, or a move to a new barn.
• Medications. Some drugs cause appetite loss.
• Systemic illness. Fever, infection, or organ disease.
• Toxin exposure. Moldy feed or toxic plants.

Red Flags That Make It an Emergency

Call your veterinarian immediately if you see any of these:

• No manure for 12 hours or more.
• Pawing, rolling, or looking at the flank. These are colic signs.
• Fever. A rectal temperature above 101.5°F in an adult horse.
• Severe drooling or inability to swallow.
• A wound that goes through the lip into the mouth [1].
• A swollen jaw or face.
• Rapid weight loss over a few days.
• Toxins. If you suspect moldy feed or a toxic plant, call your veterinarian and your regional poison control center right away.

A horse that stops eating grain but keeps eating hay is usually not in immediate danger. A horse that stops eating everything, or shows pain, is a different situation.

Safe Things You Can Do at Home

While you wait for your veterinarian, keep changes small and safe.

• Offer hay first. Let your horse eat forage while you sort out the grain issue. This helps maintain chewing and saliva flow [3].
• Check the feed. Smell the grain. Look for clumps, mold, or insects. Compare it to a fresh bag if you have one.
• Go back to the last known good batch. If you just opened a new bag, try the previous one.
• Soak the grain. Adding water can soften hard pellets and make chewing easier for a horse with mouth pain.
• Remove the grain for one meal. Skipping a single grain meal is safe for most adult horses. Do not withhold water.
• Check the mouth gently. Look for cuts, swelling, or a broken tooth, but do not pry the mouth open if your horse resists.
• Keep a simple log. Note what the horse eats, how much, and when it last passed manure.

Do not give any medication unless your veterinarian prescribes it. Doses depend on your horse's weight and health, and your veterinarian will calculate them.

For more on matching feed to your horse's needs, see Feeding Horses: Forage, Grain, and Body Condition. If you are rethinking your feeding routine, Common Horse Feeding Mistakes to Avoid covers the most frequent errors.

What Your Veterinarian Will Check and Test

Your veterinarian will start with a full physical exam, including temperature, heart rate, respiratory rate, and gut sounds. Then they will focus on the mouth and digestive tract.

Mouth and dental exam. A full oral exam with a speculum lets the veterinarian see sharp points, loose teeth, fractures, and wounds. Lip and cheek wounds may need repair, and broken teeth or bones may need additional treatment [1].

Gastroscopy. This is a camera exam of the stomach. It is the standard way to diagnose squamous and glandular gastric disease [3]. Your veterinarian may also measure intragastric pH [3].

Radiographs. For sand, radiographic imaging is considered the gold standard [2]. Your veterinarian may also use ultrasound or other imaging.

Bloodwork. A complete blood count and chemistry panel can reveal infection, organ problems, or dehydration.

Fecal and manure checks. These help rule out parasites and other digestive issues.

Feed analysis. A forage nutritive analysis can show whether your hay is meeting your horse's needs [4]. This is useful if the appetite change came with a hay switch.

Treatment depends on the diagnosis. Dental work, omeprazole, a diet change, or sand evacuation with psyllium and a laxative given by nasogastric tube are all possibilities [2][3]. Your veterinarian will choose based on the exam and test results.

Prevention and Monitoring

You cannot prevent every cause, but you can lower the odds.

• Schedule dental exams. Most adult horses need a dental check at least once a year, and more often if they have known problems.
• Change feed slowly. Mix new grain with old over several days.
• Store feed properly. Keep it dry, cool, and sealed. Use it within a reasonable time.
• Test your forage. A nutritive analysis helps you feed the right amount and spot gaps [4].
• Manage sand. If you live in a sandy area, feed from mats or raised feeders and talk to your veterinarian about sand surveillance [2][5].
• Watch the pattern. Track how long your horse takes to eat grain. A change in speed is often the first sign.
• Keep a weight tape handy. Monthly weights catch slow declines before they become serious.

If your horse is not finishing grain, write down the date it started, what changed that week, and any other signs. That history helps your veterinarian narrow the list fast.

Limitations and When to Contact a Veterinarian

This article covers common causes, but it cannot tell you what is wrong with your specific horse. Individual cases need a veterinarian who can examine the mouth, listen to the gut, and run tests.

Call the same day if:

• Your horse has refused grain for more than 24 hours.
• There is drooling, quidding, or a visible mouth wound.
• Your horse seems painful or girthy.
• You see weight loss or a dull coat.

Call now (emergency) if:

• Your horse stops eating hay too.
• There is no manure, or the manure is very dry or very loose.
• You see pawing, rolling, or flank watching.
• There is a fever, severe drooling, or a wound through the lip [1].
• You suspect sand colic or toxin exposure [2][5].

Schedule a routine visit if:

• The refusal is mild and your horse still eats hay and drinks normally.
• You want a dental exam or a forage analysis [4].
• You need help adjusting the ration.

Frequently Asked Questions

Should I be worried if my horse eats hay but not grain?

Not immediately, but it is a real sign worth investigating. Many horses with mouth pain or gastric ulcers will eat forage and refuse grain because grain is harder to chew and stimulates more acid. If the refusal lasts more than a day, call your veterinarian.

Can ulcers cause a horse to stop eating grain?

Yes. Gastric disease is a common reason for appetite changes, and grain meals tend to make stomach acid worse. A horse with ulcers may eat hay slowly and walk away from grain. Diagnosis usually requires gastroscopy, and treatment often includes omeprazole [3].

How long can a horse go without grain?

Most healthy adult horses can skip grain for a day or two without harm as long as they have good hay and water. The bigger concern is why they stopped. If your horse also cuts back on hay or water, that is urgent.

Is it safe to switch grain brands suddenly?

No. Sudden feed changes can cause refusal and digestive upset. Mix the new grain with the old over several days, increasing the new portion gradually. If your horse refuses the new feed entirely, go back to the old one and call your veterinarian.

What if my horse lives in a sandy area?

Sand accumulation is a real risk in sandy or arid regions, and it can cause inappetence and colic [2]. Feed from mats or raised feeders, and ask your veterinarian about monitoring. Radiographs are the gold standard for detecting sand [2].

If your horse's appetite change comes with other symptoms, or if you are unsure, it is always reasonable to call your veterinarian. For a broader look at appetite loss in another species, see Why Is My Dog Not Eating?.

Related Articles

• Why Is My Dog Not Eating?
• Feeding Horses: Forage, Grain, and Body Condition
• Why Is My Snake Not Eating? Causes and Solutions
• Why Does My Dog Eat Grass?
• Common Horse Feeding Mistakes to Avoid
• Dog Not Pooping but Eating Normally: Causes and Solutions

References

1. Disorders of the Mouth in Horses - Horse Owners. Merck Veterinary Manual.
2. Sand Enteropathy-What We Know So Far and Why There Is Still So Much to Learn. Animals : an open access journal from MDPI, 2026.
3. Association of Equine Squamous and Glandular Gastric Disease with Dental Status in 54 Horses. Animals : an open access journal from MDPI, 2024.
4. Forage nutritive analysis in practical equine feeding: challenges and opportunities. Journal of equine veterinary science, 2026.
5. Depth and distribution of colonic sand accumulation in a desert population of horses and its association with diagnosis of sand colic. Journal of the American Veterinary Medical Association, 2026.

Further Reading

• Merck Veterinary Manual: Horse Owners