Horses with Cushing’s disease need a low-sugar, low-starch diet to avoid dangerous spikes in insulin that can trigger laminitis. The core rule is simple: keep non-structural carbohydrates (NSC) below 10 to 12 percent of the total diet on a dry matter basis. That single threshold guides almost every feeding decision you’ll make, from hay selection to treats to pasture access.
Why Sugar and Starch Are Dangerous
Cushing’s disease, formally called pituitary pars intermedia dysfunction (PPID), disrupts your horse’s ability to regulate insulin. When a horse with this condition eats a meal rich in sugar or starch, insulin levels spike and can stay elevated for longer than normal. Roughly 90% of acute laminitis cases are linked to this kind of hormonal dysfunction, with high circulating insulin being the common thread.
That insulin doesn’t just float around harmlessly. Prolonged exposure damages the lamellar tissues inside the hoof, the delicate structures that connect the coffin bone to the hoof wall. The damage involves disrupted cell signaling, structural changes to the tissue, and reduced blood flow. The excessive consumption of non-structural carbohydrates is the primary dietary factor driving this process, which is why controlling what goes into your horse’s mouth matters so much.
Grains and Sweet Feeds to Eliminate
Cereal grains are the biggest offenders. Oats, corn, barley, and wheat are all high in starch and cause rapid blood sugar spikes. Whole oats, for example, have a glycemic index of 100, meaning they cause a significant insulin response. Some commercial sweet feeds score even higher, with glycemic index values reaching 129. These feeds were designed to pack calories into performance horses, not to be safe for metabolically compromised animals.
Remove from your feed room:
- Sweet feeds with molasses coating or syrup binders
- Whole or processed cereal grains like oats, corn, and barley
- Pelleted feeds with grain-based ingredients or added molasses
- Sugary treats including apples, carrots in large quantities, sugar cubes, and candy
If you need to add calories, a small amount of fat works better than grain. Half a cup of rice bran oil or corn oil twice a day provides energy without triggering an insulin response. Soaked, molasses-free beet pulp is another safe option for adding bulk and calories.
Reading Feed Labels for Hidden Sugars
Molasses is the most common hidden sugar source in commercial horse feeds. It’s added as a binder and flavor enhancer, and it shows up in products you might not expect, including some “complete” feeds and vitamin pellets. Always check the ingredient list, not just the front label. A feed marketed as “low starch” can still contain molasses or other sugar sources that push the NSC content above safe levels.
Look for feeds that list their NSC percentage directly. If the label only shows crude fiber, protein, and fat, you can estimate NSC by adding the starch and water-soluble carbohydrate values if they’re available. When in doubt, contact the manufacturer and ask for the full nutritional profile. For a Cushing’s horse, the combined sugar and starch content of any feed or supplement should stay well below 12%.
Choosing Safe Hay
Hay is the foundation of a Cushing’s horse’s diet, but not all hay is safe. The goal is hay with an NSC content below 10 to 12 percent on a dry matter basis. You cannot tell this by looking at it or smelling it. The only reliable way to know is a forage analysis, which most agricultural extension labs offer for a modest fee.
Mature grass hays tend to be lower in sugar than lush, early-cut hay. Timothy and orchardgrass are commonly used, but the sugar content varies enormously depending on when the hay was cut, the weather during growth, and how it was cured. A beautiful bale of timothy can test at 18% NSC while a less impressive-looking one tests at 8%. Testing is the only way to know.
If you can’t get your hay tested, soaking it in cold water reduces the sugar content. A quick 20-minute soak removes roughly 5% of water-soluble carbohydrates, which helps but isn’t dramatic. Soaking for 16 hours removes about 27%, a meaningful reduction. The practical approach is to soak for as long as you reasonably can. Hot water dissolves sugars faster than cold, so if time is limited, warm water for a shorter soak is a reasonable compromise. Drain the water completely before feeding, as it’s now sugar water you don’t want your horse drinking.
Pasture: The Overlooked Risk
Fresh pasture grass is one of the most dangerous feeds for a Cushing’s horse, and it’s the one owners most often underestimate. Lush grass can contain NSC levels well above 20%, far beyond the safe threshold. Carbohydrate-rich pasture can quickly lead to laminitis in horses with Cushing’s.
Sugar levels in grass change throughout the day and across seasons. Grass produces sugar through photosynthesis during daylight hours, so levels climb steadily and peak in the late afternoon and evening. They’re lowest in the very early morning before the sun has been up long. Cool nights make the problem worse: normally the plant uses its stored sugar overnight to fuel growth, but when nights are cold, that growth slows and the sugar stays in the leaves, ready to be eaten the next morning.
The highest-risk times of year are spring (during rapid growth) and early fall (when rain follows a dry summer and triggers a second flush of growth). Stressed grass is also dangerous. Overgrazed paddocks, drought conditions, and salty soil all cause grass to accumulate more fructans, a type of sugar that’s particularly problematic.
For many Cushing’s horses, the safest option is no pasture access at all, replaced with a dry lot and tested hay. If you do allow grazing, limit it to early morning hours, use a grazing muzzle, and avoid turnout entirely during spring growth surges and after autumn rains.
Iron-Containing Feeds and Supplements
Research in humans has shown that excess dietary iron worsens insulin resistance, and there’s reason to believe the same applies to horses. Most horses get plenty of iron from forage alone. Adding iron through supplements, mineral blocks with high iron content, or well water with elevated iron levels may be counterproductive for a horse already struggling with insulin regulation.
Check your vitamin and mineral supplements for iron content. Many broad-spectrum equine supplements include it, but a Cushing’s horse typically doesn’t need extra. A balanced vitamin and mineral supplement that complements your hay analysis, without piling on unnecessary iron, is a smarter choice.
Building a Safe Diet
The ideal diet for a Cushing’s horse is straightforward once you know the rules. Start with tested hay below 10 to 12% NSC as the primary feed. Add soaked, molasses-free beet pulp if your horse needs more calories or fiber. Include a balanced vitamin and mineral supplement to cover gaps that hay alone won’t fill. Use a small amount of oil for additional energy if needed.
Skip the grain entirely. Skip the sweet feeds, the molasses-coated anything, and the bucket of carrots as treats. Limit or eliminate pasture access depending on the time of year and your ability to monitor grass conditions. And test your hay at least once per batch, because what looks identical to last year’s delivery could have a completely different sugar profile. The effort of managing diet closely is one of the most effective things you can do to keep a Cushing’s horse sound and comfortable long-term.