Equine Performance Veterinary Practice
Delayed shedding, loss of topline, and repeated infections should not automatically be attributed to old age. Pituitary pars intermedia dysfunction, usually shortened to PPID and commonly called equine Cushing’s disease, is a progressive endocrine disorder. Recognizing it allows treatment and daily care to be directed toward the changes occurring inside the horse. [1]
How the disease develops
The pituitary is a small hormone-producing gland at the base of the brain. One region, the pars intermedia, normally receives inhibitory signals from nerve cells that release dopamine. With PPID, these nerve cells deteriorate and their regulating influence declines. Cells in the pars intermedia become more active and may multiply and enlarge. [1]
This changes production of a group of hormone fragments made from a larger precursor protein called POMC. ACTH, the hormone commonly measured in a PPID blood test, is one of these products. ACTH is therefore a useful marker of abnormal pituitary activity, but it is not the entire disease. [2]
Although the name Cushing’s is familiar, equine PPID is not simply a condition of continuously high blood cortisol. Cortisol concentrations can remain within the normal range. The location and regulation of the pituitary abnormality are central to understanding why the disease is treated with a medication that acts on dopamine receptors. [3]
What owners may notice
Early coat changes can be subtle, such as persistent longer hair under the jaw or on the legs. More advanced disease may produce a long, sometimes curly coat that fails to shed normally. Muscle loss, a more pendulous abdomen, reduced energy, excessive thirst or urination, and recurrent infections may accompany these changes. A horse does not need to show every sign to warrant evaluation. [1]
Laminitis risk requires particular attention. PPID can occur alongside insulin dysregulation, an abnormal insulin response that increases susceptibility to laminitis. Checking insulin status helps guide feeding and hoof protection; a PPID diagnosis alone does not tell us how the horse responds to dietary sugar. [2]
Why diagnosis requires interpretation
A resting ACTH test is often the starting point. Results are interpreted alongside the examination and the season, because ACTH normally changes through the year. Borderline values are not an automatic diagnosis or an automatic all-clear. Clinical context determines whether to monitor, repeat testing, or investigate further. [2]
A TRH stimulation test measures the ACTH response after administration of a stimulating hormone. It can provide additional information when early disease is suspected or the initial result is inconclusive. Testing protocols and interpretation should follow current veterinary guidance rather than a single numerical cutoff found online. [2]
How pergolide helps
Pergolide stimulates dopamine receptors, helping restore inhibitory control over pituitary hormone production. It is the standard medical treatment for PPID. Its purpose is long-term disease control, not reversal of every age-related change. Medication and monitoring generally continue throughout the horse’s life. [3, 4]
Response is evaluated through both clinical observations and blood testing. Coat quality, energy, appetite, and muscle condition should be considered alongside hormone values. Reduced appetite and lethargy can occur after starting treatment; contact your veterinarian promptly if these develop so the introduction or dose can be adjusted appropriately. Do not make ongoing dose changes based only on how the horse looks that week. [4]
Supporting the whole horse
Nutrition should reflect body condition, dental function, muscle loss, and insulin status. An underweight older horse needs adequate calories and quality protein, while a horse with insulin dysregulation also needs careful carbohydrate management. One standard diet will not meet every PPID horse’s needs. [1]
Regular dental examinations, hoof care, parasite management, and prompt attention to infections remain important. Clipping a retained coat can improve comfort in warm weather. Medication does not replace these measures, and a better coat does not necessarily mean all metabolic risks have resolved. [3]
Contact Equine Performance Veterinary Practice if changes in shedding, muscle, or health suggest PPID. A useful treatment plan connects the laboratory results to the horse’s comfort, function, and day-to-day quality of life.
Sources and further reading
[1] UC Davis Center for Equine Health — PPID
[2] Equine Endocrinology Group — 2025 PPID recommendations
[3] Merck Veterinary Manual — PPID and hypertrichosis
[4] DailyMed — Prascend prescribing information
This information does not replace veterinary advice for your individual horse.