Cushing's (PPID) in the horse

What is PPID?

Pituitary Pars Intermedia Dysfunction (PPID) — commonly known as 'Cushing's in the horse' — is a progressive neurodegenerative disorder of the pituitary gland. Due to the gradual death of dopaminergic inhibitory neurons, the pars intermedia produces excessive amounts of hormone precursors, of which ACTH is the most well-known. The condition affects almost exclusively horses older than 15 years and is not curable, but can be stabilised [3].

Recognition and diagnosis

The earliest and most recognisable sign is hypertrichosis: a long, sometimes curly coat that does not shed or sheds incompletely. Other characteristics include:

• Muscle loss along the back and upper thigh
• Increased water and urine production
• Delayed wound healing and recurring infections
• Laminitis, sometimes outside the growth season

ACTH measurement in the blood is the standard diagnostic test [2]. Important: healthy horses exhibit a physiological ACTH peak in autumn. Season-specific reference values are therefore essential to prevent over- or under-diagnosis. In early or mild PPID, the TRH stimulation test significantly increases diagnostic sensitivity [2].

What works — and what does not

Pergolide (Prascend)

Pergolide, a dopamine agonist, is the only registered medicinal product for PPID in horses. Clinical improvement occurs in more than three-quarters of treated horses [1]. However, most studies are observational and lack a placebo group, which limits the strength of the evidence. Nevertheless, pergolide is the only proven effective option and forms the basis of every PPID treatment.

Chasteberry (Vitex agnus-castus)

Chasteberry is commercially offered as a natural alternative to pergolide. In controlled studies, chasteberry does not demonstrably lower ACTH levels [3]. There is no evidence that it slows disease progression or reduces clinical signs. Chasteberry must therefore never replace pergolide, not even as a supplement without veterinary supervision.

Nutrition and management

Although nutrition does not treat PPID, the management of insulin dysregulation — a common complication — is crucial. Horses with PPID have an increased risk of laminitis due to insulin dysregulation. A low-sugar and low-starch diet, regular hoof care and weight management are supportive measures with broad veterinary consensus, although they have not been specifically investigated in PPID trials.

Supplementary ≠ replacement

PPID is a progressive condition where delay of correct treatment causes direct damage, particularly through laminitis. Supplementary measures can support quality of life, but do not replace pergolide. Regular monitoring of ACTH levels — also in treated horses — is necessary to evaluate the dosage and detect complications early [1][3].

When to go to the vet immediately?

See the red flags below. If PPID is suspected — even without all symptoms — early diagnosis is important: the earlier treatment starts, the better the prognosis for hoof health and muscle preservation.

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Sources: [1] The Veterinary Journal 2020 · [2] Equine Veterinary Journal 2022 · [3] PLoS One 2021