Why Is My Horse Losing Weight Even With Ample Hay?

You’re doing everything right. You’ve got a round bale in the corner, or you’re throwing flake after flake of good grass hay. Yet your horse’s ribs are starting to show, and the topline is melting away. It’s frustrating, worrying, and honestly, it can make you feel like you’re failing. But here’s the truth: a horse losing weight on plenty of hay is a puzzle with many possible pieces, and most of them are fixable. Let’s work through this together, owner to owner, and figure out what might be going on and what to do next.

Check the Hay Quality First, Not Just the Quantity

Before you blame your horse, take a hard look at the hay itself. Not all hay is created equal. A bale that looks green and smells sweet might still be low in digestible energy if it was cut late, rained on, or stored poorly. Mature, stemmy hay is high in fiber but low in the calories your horse can actually use. If your horse is a hard keeper, especially a performance horse, plain grass hay often won’t cut it. You might need to switch to a legume mix like alfalfa, or add a concentrated feed. Also, think about what your horse is eating day to day. If you’re training for events, their energy needs are much higher than a pasture puff. A good starting point is to get your hay tested for nutrient content, and ask your vet or an equine nutritionist about balancing it. For horses in heavy work, you’ll want to look at feeding plans that match their output, similar to what you’d find in a guide on what eventing horses eat.

Dental Pain Is a Silent Weight Killer

Horses grind their food with a side-to-side motion, and if they have sharp points, hooks, or a loose tooth, they will avoid chewing properly. They might drop wads of half-chewed hay, or you might see them dunking hay in water to soften it. Even if they swallow, they aren’t breaking down the plant material enough to extract nutrients. The result? The hay goes in, but the calories don’t get absorbed. A dental exam by a qualified equine veterinarian or equine dental technician, usually with sedation and a speculum, is non-negotiable if you’re seeing weight loss. This is not something you can eyeball by looking at the front teeth. Schedule a float at least once a year, and twice a year for seniors or horses with known issues. A horse that can chew comfortably will often start gaining weight within a few weeks.

Parasites and Gut Health Are the Hidden Thieves

Internal parasites are a classic cause of unexplained weight loss. Even with a regular deworming program, resistance is a real problem. If you’re using a single product year-round, you might be selecting for resistant worms. A fecal egg count test tells you if your horse is shedding a high load, and if so, which dewormer will actually work. Beyond worms, the hindgut is where fiber fermentation happens. If that environment is off, due to stress, antibiotics, or a sudden feed change, your horse won’t extract energy from hay properly. Look for signs like loose manure, undigested grain in the stool, or a dull coat. Adding a good probiotic or prebiotic supplement can help rebuild the good bacteria. Also, consider hindgut ulcers, which are common in performance horses and can cause poor appetite and weight loss. If your horse is in training and also showing signs of discomfort, you might want to read up on signs of lameness in eventing horses, as pain anywhere can suppress appetite.

Teeth, Worms, and Ulcers: The Triple Threat

Sometimes it’s not one thing, but a combination. A horse with mild dental issues might still eat, but not enough. Add a moderate worm burden, and now they’re losing ground. Then throw in a stressful training schedule, and you have a recipe for gastric ulcers, which can cause a horse to stop eating altogether. This is especially common in eventers and other performance horses. If you notice your horse is grumpy when you put on the girth, or seems anxious at feeding time, ulcers could be part of the puzzle. Talk to your vet about a trial of antacids or a prescription ulcer medication. Also, review your horse’s overall management. Are they getting enough turnout? Is their stable too small or too isolated? Stress is a major factor in weight loss. A calm, comfortable environment is just as important as feed. For horses in heavy work, even their stable size and setup can affect how well they rest and digest.

Age, Metabolism, and Underlying Disease

Older horses, especially those over 20, often struggle to maintain weight due to a decrease in digestive efficiency. They might have Cushing’s disease (PPID), which can cause muscle wasting and a poor coat. Or they could have insulin resistance, which makes them prone to laminitis and weight loss in odd patterns. If your horse is older, a simple blood test for ACTH and insulin can rule these out. Also, consider chronic conditions like liver or kidney disease, or even a slow-growing tumor. These are less common but shouldn’t be ignored if other causes are ruled out. Your vet is your best partner here. They can do a full workup, including bloodwork and possibly an ultrasound of the abdomen. Don’t guess with these. If your horse is also showing signs of discomfort or a change in gait, that pain can reduce appetite, so check out whether your horse’s training load is appropriate for their age and fitness level.

Practical Steps to Turn It Around

Start by weighing your hay. A flake can weigh anywhere from 3 to 6 pounds, and you need to know exactly how much your horse is getting. A typical horse needs 1.5% to 2% of their body weight in forage daily, but a hard keeper might need more. Offer hay free-choice if possible, or at least multiple small meals. Add a high-fat supplement like vegetable oil (up to 1 cup per day) or a commercial calorie booster. Beet pulp is another excellent, digestible fiber source that adds calories without sugar. Soak it or feed it dry, but always introduce it slowly. And don’t forget to check your horse’s body condition score weekly, using a chart and your hands, not just your eyes. If you’re also dealing with training issues, like a horse that’s refusing jumps or seems dull, that could be a sign of pain or fatigue, so review why your eventing horse might refuse jumps as part of a holistic check.

“A horse that is losing weight is telling you something. Listen with your eyes, your hands, and your vet’s stethoscope.”

When to Call the Vet

If your horse is losing weight rapidly, has a fever, is lethargic, or has diarrhea, call your vet immediately. Also, if you’ve addressed teeth, parasites, and feed and there’s no improvement in 4 to 6 weeks, a full veterinary workup is essential. Weight loss is a symptom, not a diagnosis. Your vet can help you create a safe, effective plan. Remember, you know your horse best. Trust your gut. With patience and a systematic approach, you can get those pounds back on and see that healthy, shiny coat again.