Horse Cushing's Disease (PPID): Managing Endocrine Disease for Welfare

Pituitary Pars Intermedia Dysfunction (PPID) is the most common endocrine disease of older horses. With correct diagnosis and treatment, affected horses can live comfortably for years.

Key Facts

PPID (Cushing's disease) occurs in approximately 20-25% of horses over 15 years of age, making it extremely common in the older horse population.
It is caused by hypertrophy of the pars intermedia of the pituitary gland, leading to excess ACTH and cortisol production.
Classic signs include a long, curly non-shedding coat (hypertrichosis), muscle wasting, pot-bellied appearance, polydipsia/polyuria, and laminitis.
PPID significantly predisposes horses to laminitis — this is one of the most serious welfare consequences of unmanaged PPID.
Diagnosis uses resting ACTH measurement or a TRH stimulation test, with seasonal adjustment for normal late-summer ACTH peaks.
Treatment with pergolide mesylate (Prascend) effectively controls PPID in most horses and reduces laminitis risk.
Regular monitoring (bi-annual ACTH testing) is required to adjust pergolide dose as the condition progresses.

Welfare Considerations

Unmanaged PPID causes a cascade of welfare problems. The long coat prevents normal thermoregulation and causes heat stress in warm months. Muscle wasting leads to weakness and reduced activity tolerance. Most significantly, PPID greatly increases laminitis risk — and laminitis, as discussed in other sections, is among the most painful conditions in equine medicine. Many horses with PPID experience their first episode of laminitis as the presenting complaint that leads to diagnosis. With pergolide treatment, PPID is highly manageable — many horses maintain excellent quality of life and remain rideable. Treatment must begin early and doses adjusted regularly. Annual coat clipping and careful nutritional management (low-sugar, high-fibre diet) complement medical treatment.

What You Can Do

Screen horses over 15 years for PPID annually with an ACTH blood test — early diagnosis prevents serious complications.
Watch for the classic signs: long non-shedding coat, muscle wasting, pot belly, and increased water intake.
Start pergolide treatment promptly when PPID is diagnosed — it is highly effective and well-tolerated.
Clip the coat of PPID horses in spring if they fail to shed — this significantly improves thermoregulation and comfort.
Feed a low-sugar, low-starch diet and restrict grazing to minimize laminitis risk in PPID horses.
Schedule bi-annual ACTH monitoring to ensure the pergolide dose remains appropriate as the disease progresses.