The very first sign of Cushing’s disease in horses is usually a change in the hair coat: it sheds later than normal in spring, or patches remain long and wavy well into summer. This subtle shift is easy to dismiss as a quirk of aging, but it’s the earliest and most reliable indicator of pituitary pars intermedia dysfunction (PPID), the condition commonly called equine Cushing’s disease. The disease is slow and progressive, meaning early signs can appear months or years before the more dramatic symptoms that most owners recognize.
Delayed Shedding: The Earliest Red Flag
Mildly affected horses may only show delayed or incomplete shedding, and even experienced horse owners can miss it. Instead of dropping their winter coat on a normal spring timeline, affected horses hold onto patches of longer hair, particularly along the jaw, belly, and legs. In the earliest stages this doesn’t look like the classic “curly, shaggy coat” associated with advanced Cushing’s. It just looks like a horse that’s a little slow to shed out.
As the disease progresses, delayed shedding develops into true hypertrichosis: a long, thick, often wavy coat that doesn’t shed at all without clipping. In pooled data from 13 studies, hypertrichosis was the single most common clinical sign in horses with PPID, present in about 70% of confirmed cases. But by the time a coat looks obviously abnormal year-round, the disease is no longer in its early stages.
What’s Happening Inside the Horse
Cushing’s disease in horses is a neurodegenerative condition, not a simple hormonal imbalance. Nerve cells in the hypothalamus that produce dopamine gradually deteriorate due to oxidative damage. Normally, those neurons send dopamine to a specific region of the pituitary gland (the pars intermedia), keeping it in check. When dopamine drops, that region becomes overactive, producing excess hormones that cascade into the symptoms owners eventually see.
Over time, the pituitary tissue itself changes, with cells first enlarging and multiplying, then eventually forming benign tumors. This is why the disease is progressive and why early detection matters: catching it when dopamine loss is mild gives treatment the best chance of controlling symptoms before the pituitary undergoes more permanent structural changes.
Early Body Shape Changes
Alongside coat changes, subtle shifts in body condition often appear early. The most common is loss of muscle along the topline, the area over the back, loin, and hindquarters. Owners frequently attribute this to aging or reduced exercise, but in a horse over 15, progressive topline wasting combined with a slow shed should raise suspicion.
Fat redistribution is another early indicator. Horses may develop abnormal fat deposits above the eyes, along the crest of the neck, or over the tailhead, even while losing muscle elsewhere. Some develop a mildly pendulous abdomen, giving them a pot-bellied appearance that wasn’t there before. These changes in fat and muscle happen gradually enough that they’re hard to notice unless you’re comparing photos over several months.
Increased Thirst and Urination
Many owners notice their horse drinking more water and producing more urine than usual. In a pasture setting this can be hard to quantify, but stalled horses will go through water buckets faster and have wetter bedding. This sign tends to appear alongside or shortly after the coat and body changes, though in some horses it’s the first thing an owner picks up on.
Excessive Sweating and Lethargy
Abnormal sweating is an underappreciated early sign. Affected horses may sweat heavily at rest or with minimal exertion, sometimes in patches rather than evenly across the body. Paired with this, many horses become noticeably more lethargic. They may seem dull, less interested in their surroundings, or slower to respond than they used to be. Both signs are easy to chalk up to heat or age, which is part of what makes early Cushing’s so easy to miss.
Laminitis: A Serious Warning Sign
Laminitis is the second most common clinical sign in PPID horses, occurring in roughly 49% of confirmed cases. Horses with PPID have nearly five times the odds of developing laminitis compared to age-matched horses without the disease. Any horse over 15 that develops unexplained laminitis, especially repeated episodes or laminitis that occurs outside of typical risk scenarios like grain overload, should be tested for Cushing’s.
The connection between Cushing’s and laminitis runs through insulin. Over a third of horses with PPID develop abnormally high insulin levels, and research has shown that laminar damage only occurs in PPID horses that also have elevated insulin, not in those with normal insulin. This means that managing insulin through diet and medication is one of the most important things you can do to protect your horse’s feet if Cushing’s is suspected or confirmed.
Recurrent Infections and Slow Healing
Because excess pituitary hormones suppress normal immune function, early-stage Cushing’s horses often develop recurrent infections. Hoof abscesses that keep coming back, skin infections that heal slowly, or respiratory infections that linger can all be early clues. Wounds that would normally close up in a week or two may take significantly longer. If your horse seems to catch everything and recover from nothing, particularly in combination with any of the signs above, it’s worth pursuing testing.
How Veterinarians Confirm the Diagnosis
The standard screening test measures a hormone called ACTH in the blood. Normal horses have ACTH levels below 29 pg/ml for most of the year, but there’s a natural seasonal rise between August and October when the upper limit shifts to 47 pg/ml. This seasonal variation matters: a result that looks borderline in March might be completely normal in September. Your vet will account for the time of year when interpreting results.
For horses with subtle or early signs where resting ACTH is borderline, a stimulation test can improve accuracy. The horse receives an injection that stimulates the pituitary, and ACTH is measured again 10 minutes later. Horses with early PPID produce an exaggerated response, making the test more sensitive for catching the disease before resting levels become obviously abnormal. Testing during the autumn rise (August through October) can also increase sensitivity for detecting early cases.
What Happens After Diagnosis
Treatment centers on replacing the dopamine the brain is no longer producing in adequate amounts. The standard medication is given orally once daily, and most horses start to show measurable improvement within the first three months. Coat changes respond best: in clinical trials, about 33% of horses showed improvement in hair coat by day 90, climbing to 89% by day 180. Other signs improve more modestly. About 46% of horses showed improvement in muscle wasting by six months, and roughly 34% showed reduced drinking and urination.
Treatment is lifelong and the dose may need adjustment over time as the disease progresses. Your vet will typically recheck hormone levels around 90 days after starting medication to determine whether the dose is adequate. Beyond medication, dietary management plays a critical role, particularly limiting sugars and starches in feed and forage to control insulin and reduce laminitis risk.
What to Watch in an Aging Horse
Because Cushing’s is a disease of older horses, every sign overlaps with normal aging. The key is pattern recognition: not one sign in isolation, but a cluster that develops over months. A horse over 15 that sheds late, loses topline muscle, drinks more, and develops a dull attitude isn’t just getting old. Taken together, those signs paint a clear enough picture to justify a blood test, and early treatment can meaningfully slow the progression of symptoms and protect against laminitis.