Horses with Cushing’s disease need a diet built around low-sugar forage, with total non-structural carbohydrates (NSC) kept below 10 to 12% in all hay and feeds. The core goal is managing insulin levels, since most horses with Cushing’s develop some degree of insulin dysregulation, which raises their risk of laminitis. Getting the diet right can make a significant difference in comfort, weight, and hoof health.
Why Sugar and Starch Are the Main Concern
Cushing’s disease, formally called pituitary pars intermedia dysfunction (PPID), disrupts hormone regulation in a way that often impairs how the body handles sugar. When a horse with PPID eats feeds high in sugar and starch, blood glucose and insulin spike more than they should. Chronically elevated insulin is one of the primary drivers of laminitis, and horses with Cushing’s are already at heightened risk.
This means the entire diet needs to be evaluated through the lens of NSC content. NSC is the combined measure of sugars and starches in a feed or forage. Avoid any concentrate feed with more than 20% NSC or more than 3% added molasses. For hay, the target is even tighter: under 10 to 12% NSC.
Choosing and Testing Your Hay
Hay is the foundation of any horse’s diet, and for a Cushing’s horse it deserves extra scrutiny. You can’t tell NSC content by looking at hay or smelling it. The only reliable way to know is to send a sample to a forage testing laboratory. On the report, look for the NSC value, which combines water-soluble carbohydrates (WSC) and starch. You want that combined number under 10 to 12%.
If your hay tests above that threshold, soaking it in water before feeding can help. Soaking for 15 to 60 minutes pulls soluble sugars out of the hay. Research from the University of Minnesota Extension found that grass hays starting above 12% NSC dropped to around 10 to 12% after just 15 to 30 minutes of soaking. It’s not a perfect fix for extremely high-sugar hay, but it’s a practical tool. Drain the water completely before feeding, and in warm weather, soak in smaller batches to prevent fermentation.
Mature grass hays tend to be lower in sugar than lush, early-cut hay. Timothy, orchard grass, and Bermuda are commonly available options, but the specific NSC still varies by cutting, climate, and growing conditions. Testing is always worth the small cost.
Managing Pasture Access
Fresh grass is often the most dangerous sugar source for a Cushing’s horse, and many owners underestimate it. Sugar levels in pasture grass fluctuate dramatically throughout the day and across seasons.
Plants produce sugars during photosynthesis while the sun is shining, then burn through those sugars overnight to fuel growth. This means NSC levels are highest at the end of the afternoon and lowest in the early morning before sunrise. If you allow any grazing at all, early morning turnout is the safest window.
There’s an important exception: when overnight temperatures drop to around 40 to 45°F, the plant’s ability to use up its stored sugars slows dramatically. The sugars that normally deplete overnight stay locked in the grass, so even early morning levels remain high. Spring and fall are particularly risky seasons for this reason. Many owners of Cushing’s horses use a grazing muzzle or switch to a dry lot during these periods to eliminate the risk entirely.
Short, stressed, or frost-damaged grass can also concentrate sugars. A sparse pasture is not necessarily a safe one.
Safe Ways to Add Calories
Many horses with PPID lose muscle and body condition, especially as the disease progresses. Replacing those calories with grain or sweet feed would spike insulin, so you need alternative energy sources that are low in sugar and starch.
Unmolassed beet pulp is one of the best options. Despite coming from sugar beets, the sugar has been extracted during processing, leaving a highly digestible fiber source that provides roughly the same calories per pound as oats. It’s low enough in NSC to be safe for insulin-sensitive horses, as long as you buy the version without added molasses. Beet pulp also has good calcium content and protein comparable to grass hay (8 to 12%), making it a solid all-around addition.
Soy hulls are another fiber-based feed that provides energy without a sugar load. Both beet pulp and soy hulls are sometimes called “super fibers” because they ferment efficiently in the hindgut, delivering steady energy rather than a glucose spike.
Fat is another useful calorie source. Feeds with more than 6% fat content are preferred for Cushing’s horses because they rely less on carbohydrates for energy. You can also top-dress meals with vegetable oil, starting at half a cup twice daily and working up to one cup twice daily. Stabilized rice bran is an alternative, fed at roughly double the volume of oil. Adding 1 to 2 ounces of a marine-derived fish oil per day may offer additional benefit: the omega-3 fatty acids EPA and DHA have been shown to improve glucose tolerance in horses on higher-fat diets.
Alfalfa hay or chaff can also help a thin horse. It’s calorie-dense and higher in protein than grass hay, which supports muscle maintenance. Some owners worry about alfalfa for metabolic horses, but its NSC is generally moderate, and the protein and calorie density can be valuable for horses struggling to hold weight. Use it as a supplement to your tested grass hay rather than a full replacement.
Protein and Muscle Loss
Muscle wasting along the topline, neck, and hindquarters is one of the hallmark signs of Cushing’s. This happens partly because the hormonal imbalance shifts the body toward breaking down muscle tissue. Research has found that horses with poorly controlled PPID have significantly elevated levels of glutamine, an amino acid involved in regulating muscle synthesis and breakdown, suggesting the disease actively disrupts normal muscle metabolism.
Supporting muscle maintenance means providing adequate quality protein. Look for feeds or supplements that supply essential amino acids, particularly lysine, methionine, and threonine, which are the most commonly limiting amino acids in typical horse diets. A ration balancer designed for metabolic horses can fill this gap without adding excess sugar. These products deliver concentrated protein, vitamins, and minerals in a small serving size.
Minerals and Supplements Worth Considering
Horses with Cushing’s often benefit from a few targeted additions beyond their base diet. Magnesium plays a role in insulin signaling, and many horse diets are marginally deficient in it. Chromium, a trace mineral, is also involved in carbohydrate metabolism and is commonly included in supplements marketed for metabolic horses. A typical metabolic supplement provides around 10 grams of magnesium and 12 milligrams of chromium per daily serving for an average-sized horse.
A good vitamin and mineral supplement or ration balancer is important regardless, since low-NSC diets that restrict concentrates and pasture can leave gaps in copper, zinc, selenium, and vitamin E. Salt should be available free-choice, and fresh water is especially critical because Cushing’s horses often drink and urinate more than normal.
What About Chasteberry Supplements?
Chasteberry (Vitex agnus-castus) is widely sold as a natural treatment for Cushing’s, but the clinical evidence is discouraging. A study directly comparing chasteberry extract to the standard medication pergolide found that chasteberry did not lower elevated ACTH levels or improve clinical signs. Only 1 of 14 horses in the study remained stable on chasteberry, and in most horses, ACTH levels actually doubled over four to six months of treatment. Pergolide, by contrast, reduced ACTH to less than half of pre-treatment values in four out of six horses within a month. The researchers explicitly advised against using chasteberry for Cushing’s. Diet matters enormously, but it works alongside veterinary treatment, not as a replacement for it.
Putting It All Together
A practical feeding plan for a Cushing’s horse looks something like this: tested grass hay with NSC under 12% as the dietary backbone, fed at 1.5 to 2% of body weight daily. If the hay runs high in sugar, soak it for 30 to 60 minutes before feeding. Limit or eliminate pasture access, especially during spring, fall, and any period when overnight temperatures drop below 45°F. If the horse needs more calories, add unmolassed beet pulp, soy hulls, or vegetable oil rather than grain. Use a ration balancer or vitamin-mineral supplement formulated for metabolic horses to cover protein and micronutrient needs. Keep molasses-containing feeds, sweet feeds, and treats like apples and carrots to a minimum or avoid them entirely.
Feeding a horse with Cushing’s takes more planning than feeding a healthy horse, but the principles are straightforward: keep sugar and starch low, provide calories through fiber and fat, and make sure protein and mineral needs are met. Consistent dietary management, combined with appropriate veterinary care, gives these horses the best chance at staying comfortable and sound.