What is PPID (Cushing’s Disease) and how do I recognise and support my horse who has it?

PPID, short for Pituitary Pars Intermedia Dysfunction, is what most people mean when they say a horse has Cushing's disease. It's a disorder of the pituitary gland, the small structure at the base of the brain that controls hormone output, and it's one of the most common conditions we diagnose in older horses.

Here's the mechanism, in plain terms. A cluster of nerve cells in the hypothalamus produces dopamine, and dopamine normally keeps one part of the pituitary gland, the pars intermedia, in check. In horses with PPID, age-related oxidative stress damages those dopamine-producing cells [1]. Once that brake fails, the pars intermedia enlarges and starts overproducing hormones, including adrenocorticotropic hormone, or ACTH.

ACTH tells the adrenal glands to make cortisol. In a healthy horse that's a short, self-limiting loop. In a horse with PPID, it runs almost continuously, so cortisol stays elevated day after day. That constant cortisol exposure is what causes the damage: it disrupts metabolism, muscle maintenance, fat distribution, coat growth, and insulin sensitivity, all at the same time.

A blood test is the only way to confirm it. Your vet will measure ACTH, ideally against a reference range adjusted for the season, since ACTH rises naturally in every horse, healthy or not, between August and October [2]. Testing in autumn without accounting for that seasonal rise is a common reason horses get missed, or get flagged when they shouldn't be.

What is the role of nutrition in managing PPID symptoms?

Pergolide is still the frontline treatment: a dopamine receptor agonist that lowers ACTH production directly. But medication rarely tells the whole story on its own. Diet, tailored to body condition, insulin status, age, and workload, is now recognised as just as important for controlling symptoms and cutting laminitis risk [4]. We walk through that feeding plan step by step, with worked examples, in our companion article on nutrition for horses with PPID.

What are the main symptoms of PPID?

Symptoms vary a lot from horse to horse, and they shift as the disease progresses. Early on, the signs are easy to miss. Later, they're not.

Watch for these signs

• Laminitis, often in horses whose insulin function is already impaired.
• Hypertrichosis: a long, wavy or curly coat.
• Hirsutism: trouble shedding out fully in spring.
• Weight loss and muscle wasting, sometimes alongside a pot belly at the same time.
• Abnormal fat distribution: pads above the eyes, a cresty neck, fat on the tail head.
• Lethargy, tied to both the loss of dopamine signalling and the constant cortisol load.
• Polyuria and polydipsia: drinking and urinating noticeably more than usual.
• More frequent infections, since chronic high cortisol suppresses immune function.

A long, curly coat has traditionally been treated as the giveaway sign of PPID, but that mainly holds once the disease is advanced [1]. Earlier on, the only clue might be a coat that looks slightly duller than normal, or a horse that just seems a bit flat. Owners usually notice the coat change before I do on a routine exam, which is exactly why regular observation at home matters more than waiting for something dramatic. If something looks off, book the blood test rather than watching and waiting another season.

What is the link between PPID and insulin dysregulation?

Insulin's job is to move sugar out of the blood and into cells so they can use it for energy. In insulin dysregulation, cells stop responding properly to that signal, so glucose lingers in the blood longer than it should. The pancreas reads that as "not enough insulin" and pushes out even more, which only adds to the problem.

In horses with PPID, the same broken feedback loop that lets ACTH run high also keeps cortisol elevated, and cortisol makes cells less sensitive to insulin in the first place. The two conditions reinforce each other. About one in three horses with PPID go on to develop insulin dysregulation, and that group carries a meaningfully higher laminitis risk than PPID horses with normal insulin function [5].

How is PPID treated?

PPID is a chronic condition. It can't be cured, but it can be managed. Pergolide, a dopamine receptor agonist, reduces ACTH production and, in turn, cortisol output, which usually softens the severity of symptoms over weeks to months.

Nutrition and regular veterinary follow-up matter just as much as the medication itself. Body condition, insulin status, age, and activity level all shift over time, so a feeding plan built for a 16-year-old horse at diagnosis often needs revisiting a few years later. That's the detailed, practical part, and it deserves its own space rather than a rushed paragraph here, so we've put the full step-by-step approach in the companion nutrition article linked above.

Conclusion

Recognising PPID early rarely comes down to one dramatic symptom. It's usually a coat that sheds a little later than it used to, a horse that's slightly flatter than usual, or a vague sense that something isn't quite right. None of that is a diagnosis on its own, but it's reason enough to ask your vet for an ACTH test.

Combined with the right medication, a feeding plan matched to your horse's body condition and insulin status, and regular follow-up, most horses with PPID keep a good quality of life for years after diagnosis.