Equine Cushing's Disease (PPID): Welfare Management

Pituitary Pars Intermedia Dysfunction (PPID) in Horses

Pituitary Pars Intermedia Dysfunction (PPID), commonly called Equine Cushing's Disease, is the most common endocrine disorder of horses, ponies, and donkeys. It occurs due to progressive loss of inhibitory dopaminergic neurons controlling the pituitary pars intermedia, leading to overproduction of ACTH and related hormones. PPID is predominantly a disease of older animals — prevalence rises sharply after age 15, with estimates suggesting 15–25% of horses over 15 years are affected. As equine lifespans increase with improved healthcare, PPID welfare management becomes increasingly important.

Clinical Signs and Welfare Impact

PPID produces a wide range of clinical signs, many of which cause ongoing welfare compromise:

Classic Signs

Hypertrichosis: Long, curly, often wavy coat that fails to shed (most recognisable sign); causes heat stress, sweat accumulation, and skin infections
Laminitis: Recurring or persistent laminitis is one of the most serious welfare consequences; caused by insulin dysregulation associated with PPID
Muscle wasting: Progressive loss of topline musculature despite maintained appetite
Pot-belly: Loss of abdominal muscle tone
Polydipsia/polyuria: Increased drinking and urination
Sweating: Abnormal, often patchy sweating

Less Obvious Signs (often underappreciated)

Immunosuppression — increased susceptibility to infections (dental disease, skin infections, respiratory disease)
Neurological signs — blindness, seizures in advanced disease
Poor wound healing
Subtle behavioural changes — reduced responsiveness, apparent lethargy

Diagnosis

PPID diagnosis is primarily clinical, supported by laboratory testing:

Resting plasma ACTH: Most widely used; elevated in PPID. Seasonal reference ranges required (ACTH rises naturally in autumn — using non-seasonal thresholds misclassifies horses)
TRH stimulation test: More sensitive for early/mild PPID; measures ACTH response to TRH injection. Gold standard for early diagnosis
Insulin measurement: Important for laminitis risk stratification; many PPID horses have concurrent insulin dysregulation

Treatment: Pergolide (Prascend)

Pergolide mesylate (Prascend — licensed equine formulation) is the mainstay of PPID treatment, acting as a dopamine agonist to restore pars intermedia regulation. Key clinical evidence:

Reduces circulating ACTH and associated clinical signs
Coat quality improves in 60–80% of treated horses within 3–6 months
Laminitis occurrence reduced in horses on treatment
Immunosuppression partially reversed — treated horses show fewer secondary infections

Starting dose: 2 μg/kg daily; titrate based on clinical response and ACTH reassessment at 4–6 weeks. Treatment is lifelong — dose requirements often increase over time as disease progresses.

Welfare-Centred Management Beyond Medication

Coat and Skin Care

Clip horses with severe hypertrichosis — prevents hyperthermia in warm months, allows monitoring of body condition and skin health
Regular body clip (every 4–8 weeks in severely affected animals)
Manage rugging carefully — balance warmth need (older horses) against overheating (retained coat)

Laminitis Management

Dietary management: restrict non-structural carbohydrates (NSC <10% DM total diet)
Regular farriery — every 4–6 weeks; appropriate breakover modification
Soft ground or deep bedding for laminitic horses
Monitor foot pulses and digital temperature daily during laminitic episodes

Dental and Weight Management

PPID horses frequently have accelerated dental disease. 6-monthly dental examinations are recommended. Monitor body weight and body condition monthly — both obesity and wasting can develop.

Quality of Life and End-of-Life Considerations

Many horses with well-managed PPID maintain good quality of life for years. However, advanced disease — particularly intractable laminitis, severe neurological involvement, or extreme debilitation — requires honest assessment of quality of life. Work with your veterinarian to establish welfare thresholds for euthanasia in advance of crisis.