Cushing’s Disease is a common health concern for horses—especially as they age.
However, Cushing’s Disease can even occur in younger horses. That’s why early diagnosis and proper management of Cushing’s Disease in horses is vital.
In this guide, you’ll learn more about the signs and symptoms of Cushing’s Disease, how it’s diagnosed, and the best ways to treat, manage and feed horses with Cushing’s Disease.
What is Cushing's Disease in Horses?
Cushing’s Disease, also known as Pituitary Pars Intermedia Dysfunction (PPID), occurs when a horse’s pituitary gland becomes enlarged and functions improperly. This leads to the excessive production of multiple pituitary hormones, including Adrenocorticotropic Hormone (ACTH).
Although PPID is often considered an “old horse” disease, it has been diagnosed in horses as young as seven years old. When detected early, it can often be treated with medication, diet and other equine management practices.
Signs and Symptoms of Cushing's Disease in Horses
Depending on the severity and stage of Cushing’s Disease in horses, the symptoms of PPID can vary.
Common and early symptoms of Cushing's Disease in horses include:
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Delayed shedding of the winter coat
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Increased hair growth (hirsutism)
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Weight gain
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Muscle wasting
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Lethargy
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Increased thirst and urination
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Laminitis (inflammation of the hoof)
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Recurring infections
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Abnormal fat deposits
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Slow wound healing
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Changes in energy levels or performance
In advanced cases of PPID, horses may also develop symptoms such as:
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An excessively long, non-shedding hair coat
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Abnormal sweating patterns
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Excessive drinking and urination
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Muscle wasting (most noticeable along the topline)
However, it’s important to note muscle loss may occur with or without overall weight loss.
Diagnosing Cushing's Disease in Horses
Diagnosing Cushing’s Disease in horses involves looking at a horse’s health history, clinical signs and performing specific hormone tests.
Unfortunately, the diagnosing of Cushing’s Disease isn’t always straightforward due to a few factors:
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The disease progresses slowly, making it harder to spot early on
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Early tests can often give false negative results
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Tests become more accurate as the disease advances
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Hormone levels can vary with the seasons which could cause false negatives in some seasons
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There isn’t a single foolproof test to confirm the disease
The two tests most commonly used to help diagnose Cushing’s Disease in horses are the dexamethasone suppression test (DST) and ACTH (adrenocorticotropic hormone) stimulation test.
Dexamethasone Suppression Test:
In this test, a veterinarian draws blood, administers a dose of dexamethasone, and then takes another blood sample about 19–24 hours later. The low-dose version is typically used to diagnose Cushing's Disease and determine whether it’s pituitary or adrenal related. A high-dose version can help distinguish Cushing's Disease from other conditions.
ACTH Stimulation Test:
For this test, blood is drawn into an EDTA collection tube, and the plasma is separated from the cells. ACTH levels are then measured to differentiate between ACTH-dependent and ACTH-independent forms of Cushing’s Disease.
Some horses with PPID also develop Equine Metabolic Syndrome. Testing PPID horses for Equine Metabolic Syndrome can provide valuable insight into their metabolic status and help further specify their dietary needs.
Treating and Managing Cushing's Diseases in Horses
While there’s no true cure for Cushing’s Disease in horses, proper medical treatment, care and nutrition can help manage and suppress PPID symptoms or improve the quality of life for a horse with Cushing’s Disease.
One way is to regularly body clip horses with Cushing’s Disease, as their coats can become thick even year-round. This overly long coat can make them uncomfortable during warmer months or for those living in a warmer climate. Exercise, as well as consistent dental and hoof care, are also vital care management strategies for horses with Cushing’s Disease.
For horses diagnosed with Cushing’s Disease, a commonly used medication to manage PPID is Pergolide. This medication acts as a dopamine activator, boosting dopamine levels in the horse’s brain to help regulate the hormone overproduction caused by Cushing’s Disease. Because Pergolide mimics dopamine, it helps restore normal pituitary function, which is disrupted with PPID, leading to reduced cortisol production. By increasing dopamine activity, Pergolide can reduce common signs of Cushing’s Disease, such as excessive hair growth, lethargy, increased drinking and urination, and laminitis. Some horses might experience side effects on Pergolide like a reduced appetite.
However, Pergolide is still typically given alongside a dietary adjustment tailored to the horse’s specific needs.
Adjusting the diet of horses with PPID is a vital part of Cushing’s Disease management in horses. Horses with Cushing’s Disease often struggle with high blood sugar and insulin resistance, meaning their cells don’t respond well to insulin. Insulin is responsible for helping cells absorb sugar, but when it doesn’t work properly, the sugar stays in the bloodstream and gets stored as fat. This results in the abnormal fat distribution commonly seen in horses with PPID.
When feeding horses with Cushing’s Disease, several dietary factors should be considered. Providing high-quality protein is essential to support muscle maintenance, build muscle back, and help mitigate muscle wasting as much as possible. It’s important to be realistic, however—horses in the advanced stages of the disease with significant muscle loss may not fully regain their pre-disease muscle condition.
When aiming to build muscle, people often focus too much on the crude protein percentage in feed. However, switching from a 10% or 12% crude protein feed to a 14% feed typically won’t make a significant difference.
What matters more is the feed’s fortification with key amino acids, such as lysine, methionine, and threonine, which are often deficient in the forage portion of a horse’s diet. Vitamin E and C are also known to be helpful additions to the horse’s diet when they have Cushing’s Disease.
Finding the Best Feed for Horses with Cushing's Disease
Tribute® Superior Equine Nutrition generally recommends feeding horses with Cushing’s Disease, and those horses who also develop Equine Metabolic Syndrome, a low NSC diet. A low NSC (non-structural carbohydrate) diet is also ideal for horses with other metabolic issues such as insulin resistance, laminitis or obesity.
Kalm ‘N EZ® Pellet is ideal for moderate to hard-keeping horses with sugar and starch sensitivities, including those with PPID, Insulin Resistance, PSSM Type 1 and other metabolic disorders. The low sugar and starch (NSC) content also makes it a great choice for hyperactive horses and those with sensitive digestive tracts. Because of high fiber content, Kalm ‘N EZ® is an excellent option when hay quality is poor or hay replacement is needed. This feed is also formulated with prebiotics and probiotics to support your horse’s digestive health.
By significantly reducing sugar and starch intake in their diet, this helps regulate blood sugar levels and supports digestive health, especially for horses with sensitive digestive systems. While managing NSC intake levels in a horse’s grain is important, forage typically contributes to the majority of a horse’s NSC intake and should also be carefully monitored.
Easy-keeper horses with Cushing’s Disease might do better on a ration balancer, such as Essential K®. Essential K® adds a boost of essential vitamins and nutrients, but only minimal amounts of NSC to the horse’s diet. To support PPID horses, Tribute® Nutrition often recommends adding 1 to 2 pounds of Essential K® to their diet for a concentrated boost of topline-supporting amino acids.
Weight loss can also be a symptom of Cushing’s Disease in some horses. These horses will likely need additional calories in addition to their normal forage intake. Adding a fat supplement, like K Finish®, to the horses ration balancer is a great option for adding more calories to the horses diet.
Another option is to feed a full-intake feed that is also low NSC, such as Kalm N’ EZ® or Senior Sport. Kalm ‘N EZ® and Senior Sport® are both popular options to support the harder-keeping horses with Cushing’s Disease. Essential K® can also still be added to either of these feeds to maintain topline muscling as discussed above.
If you need help finding the perfect feed for a horse with Cushing’s Disease, you can also get a personalized feeding plan with Tribute® Superior Equine Nutrition to ensure your horse is getting exactly what they need nutritionally.
