PPID in Horses (Equine Cushing's) Explained
PPID, or equine Cushing's, is the most common hormone disease of older horses. Learn what it is, how ACTH testing and pergolide work, and the laminitis link.
Quick definition: PPID (pituitary pars intermedia dysfunction), historically called equine Cushing's disease, is a slow-progressing hormonal disorder of the pituitary gland that mainly affects horses over 15. The enlarged pars intermedia overproduces hormones such as ACTH, leading to a delayed shaggy coat, muscle loss, increased drinking, and a higher risk of laminitis. It is diagnosed by a blood ACTH test and managed for life with daily pergolide.
If your veterinarian has mentioned PPID or equine Cushing's, you are dealing with the most common hormonal disease of senior horses. It is not a death sentence. With early diagnosis and daily medication, most affected horses stay comfortable and active for years.
PPID develops gradually as a small part of the pituitary gland, the pars intermedia, loses its normal regulation and enlarges. That overgrowth drives the hormone changes behind the signs owners notice, from a coat that will not shed to repeated, unexplained laminitis.
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What PPID Actually Is
The pituitary gland sits at the base of the brain and helps regulate hormones throughout the body. The pars intermedia is one of its lobes. In a healthy horse, the brain chemical dopamine keeps this lobe in check. In PPID, the dopamine-producing nerves degenerate with age, the brake comes off, and the pars intermedia enlarges and overproduces hormones, including ACTH (adrenocorticotropic hormone) and related compounds.
This is why the modern name, pituitary pars intermedia dysfunction, replaced the older equine Cushing's. It names the exact location and the actual problem rather than borrowing a label from a different disease in other species.
Why PPID Matters for Senior Horses
PPID is strongly tied to age. Research suggests the disease is uncommon in young horses but increasingly likely past 15, and a large share of horses in their 20s show some degree of it. Because it progresses slowly, signs can creep in over years and be dismissed as normal aging.
- A long, curly coat that sheds late or incompletely, called hypertrichosis, the most specific sign.
- Loss of topline muscle and a potbellied appearance even when the horse eats well.
- Increased drinking and urination.
- Lethargy, a dull attitude, or reduced performance.
- Repeated or hard-to-explain bouts of laminitis.
- Slow wound healing and a higher rate of infections.
How PPID Is Tested
The first-line test is resting ACTH, measured from a single blood sample. ACTH naturally rises in late summer and autumn, so good labs use season-adjusted reference ranges to avoid false positives. For early or borderline cases, a TRH stimulation test gives a clearer answer. Many vets also run an insulin or oral sugar test, because insulin status drives the laminitis danger.
| Test | What It Shows |
|---|---|
| Resting ACTH | Screening test for PPID; interpret against seasonal ranges |
| TRH stimulation | More sensitive for early or borderline PPID |
| Insulin / oral sugar test | Identifies insulin dysregulation and laminitis risk |
Treatment and Daily Management
The cornerstone treatment is pergolide, given as a small daily oral tablet (marketed for horses as Prascend). It restores some of the missing dopamine signal, calming the overactive pars intermedia. Many horses show a better coat, more energy, and lower laminitis risk within a few months. Treatment is lifelong, and your vet will recheck ACTH to confirm the dose is right.
Medication is only half the plan. Diet matters just as much, especially when insulin is high. A low-sugar, low-starch ration, careful weight control, attentive farrier work, and routine monitoring round out the program. For feeding specifics, see our guide to feeding a Cushing's horse and the broader picture in PPID and Cushing's in senior horses.
The Laminitis Connection
The most serious risk in PPID is laminitis. Many affected horses also have insulin dysregulation, and high blood insulin can directly damage the laminae inside the hoof. That is why controlling diet, monitoring insulin, and keeping up with pergolide are not optional extras. They are the main way to keep a PPID horse sound. Keeping dietary NSC low is central to that effort.
This page is educational and does not replace your veterinarian. PPID is diagnosed and treated by a vet, and every horse needs an individual plan based on its tests, age, and history.
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Frequently Asked Questions
What does PPID stand for in horses?
PPID stands for pituitary pars intermedia dysfunction, the modern name for what owners long called equine Cushing's disease. The pars intermedia is a small region of the pituitary gland at the base of the brain. In PPID it grows and overproduces hormones, most notably ACTH. The condition is most common in horses over 15 and becomes more likely with each year of age.
What are the early signs of PPID in a senior horse?
Early PPID can be subtle: a coat that sheds late or unevenly, slight loss of topline muscle, drinking and urinating a little more, and unexplained bouts of laminitis. The classic long, curly coat that fails to shed, called hypertrichosis, usually appears later. Because early signs are easy to miss, many vets test older horses at the first hint of a delayed shed or a laminitis episode.
How is PPID diagnosed?
The most common test measures resting ACTH in a single blood sample, ideally interpreted against season-adjusted reference ranges since ACTH rises naturally in autumn. A TRH stimulation test can catch earlier or borderline cases. Your vet may also check insulin, since many PPID horses also have insulin dysregulation. Diagnosis combines test results with the horse's age, history, and physical signs.
How is PPID treated?
The standard treatment is pergolide, a daily oral medication sold for horses as Prascend. It acts on the pituitary to reduce hormone overproduction and often improves coat, energy, and laminitis risk within a few months. Treatment is lifelong, and your vet will recheck ACTH to fine-tune the dose. Pergolide is paired with careful diet, hoof care, and routine monitoring.
Why does PPID increase laminitis risk?
Many horses with PPID also have insulin dysregulation, and high circulating insulin is a direct trigger for laminitis. The hormonal changes of PPID can worsen this picture, so an uncontrolled PPID horse may founder seemingly out of nowhere. Managing PPID with pergolide, keeping dietary sugar and starch low, and monitoring insulin all help lower that laminitis risk.
Can a horse live a normal life with PPID?
Yes. With a confirmed diagnosis, daily pergolide, a low-sugar low-starch diet, attentive hoof care, and regular vet rechecks, many PPID horses stay comfortable and active for years. The keys are catching it early, controlling insulin and laminitis risk, and not skipping medication. PPID is managed rather than cured, so consistency matters more than any single intervention.
Is PPID the same as Cushing's disease in dogs and people?
No, the mechanisms differ. In dogs and people, Cushing's usually involves the adrenal glands or a different part of the pituitary and excess cortisol. Equine PPID arises specifically in the pars intermedia and centers on different hormones. The old name stuck for convenience, but PPID is the accurate term and explains why equine testing and treatment are unique to horses.
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