Equine Cushing’s Disease | Causes, Symptoms, and Treatment

14 January 2026

Cushing’s in horses, more correctly known as Pituitary Pars Intermedia Dysfunction (PPID), is the most common hormonal disorder of older equines. It is the condition most likely to be sitting quietly behind a scruffy looking coat, an unexplained laminitis episode, or a senior pony that is just not quite right. It is thought to affect around 20% of horses and ponies over the age of 15, which is a figure most yards underestimate badly.

This guide explains how Cushing’s disease in horses develops, the early warning signs vets actually look for, how the condition is diagnosed and treated, and how to manage an affected horse day to day. It is written for UK and South African owners, and the dosing, testing and competition rules quoted here are taken directly from the UK product licence, the Equine Endocrinology Group recommendations and the current FEI Equine Prohibited Substances List.

A note on this update. This article was rewritten in August 2026 after a full fact-check against primary sources. Three figures in the previous version were wrong, including the pergolide starting dose, which was stated at roughly half the licensed amount. They have been corrected against the UK Summary of Product Characteristics and are flagged in the relevant sections below. Dosing decisions are always your vet’s to make, never an article’s.

What Is Cushing’s Disease in Horses?

Cushing’s disease in horses is a progressive endocrine disorder caused by degeneration of the dopamine-producing neurones in the hypothalamus. Normally these neurones release dopamine to suppress the pars intermedia, the middle lobe of the pituitary gland sitting at the base of the brain. When dopamine production falls with age, the pars intermedia is left unrestrained and enlarges, releasing excessive quantities of pro-opiomelanocortin (POMC) derived hormones, most importantly ACTH (adrenocorticotropic hormone) along with alpha-MSH and beta-endorphin.

Despite the raised ACTH, blood cortisol concentrations in a horse with PPID usually stay within the normal range, although they lose their normal daily rhythm (Merck Veterinary Manual), and it is this disrupted hormone signalling that produces the clinical picture. The mechanism is genuinely different to human Cushing’s syndrome, which the NHS describes as too much cortisol, most often from long-term high-dose steroid medicines and sometimes from a growth in the pituitary or adrenal glands: in the horse, dopaminergic neurodegeneration is the primary fault. That is why the modern preferred term is PPID, and why the treatment of choice is a dopamine agonist rather than surgery.

It is worth being clear about one thing that trips owners up. PPID is not a disease of overfeeding and it is not the owner’s fault. It is an age-related neurodegenerative condition, closer in mechanism to Parkinson’s disease in people than to any dietary disorder. Diet matters enormously in managing it, but diet did not cause it.

Which Horses Get PPID? Age, Breed and Risk Factors

PPID is overwhelmingly a disease of the older equine. Cases under 10 are rare, and most horses are diagnosed in their late teens or older. Donkeys are commonly affected and tend to be diagnosed later, because their heavy winter coats hide the early hair coat changes.

Native and pony breeds appear over-represented in clinical caseloads, though it is debated whether this reflects a true breed predisposition or simply that natives live longer and are more likely to be insulin-dysregulated to begin with. Breeds frequently flagged include:

Welsh ponies and cobs, including the Welsh Cob
Shetland ponies, often diagnosed alongside Equine Metabolic Syndrome
Highland, Connemara, Dartmoor and Exmoor ponies
Donkeys and mules
Morgan horses

Thoroughbreds and Warmbloods are not protected. They are simply diagnosed less often, partly because they are more likely to have been retired or sold on before the signs become obvious, and partly because, as covered in the diagnosis section below, they naturally run lower ACTH values and so sit further from the diagnostic cut-off. Any horse over 15 showing one or more of the signs below deserves a blood test, whatever its breeding.

Early Signs of Cushing’s in Horses

The single most useful thing an owner can do is learn the early signs, because the late signs, meaning a full curly coat, a pot-bellied outline and laminitis, represent disease that has been progressing for years. Early indicators include:

Delayed shedding, with the winter coat still patchy on the legs and belly well into late spring
Longer guard hairs, particularly under the jaw and down the back of the legs
Loss of topline muscle over the back and quarters despite adequate feed
Mild lethargy or a change in attitude, the pony who has just slowed down a bit
Regional fat deposits: a cresty neck, supraorbital fat above the eye, and a tail-head pad
Recurrent low-grade laminitis, often presenting as a footy episode after spring grass that never quite resolves
Mildly increased drinking and urination (polydipsia and polyuria)
Slow wound healing, and recurrent skin problems such as mud fever that is harder to shift than usual

Muscle loss is the sign most often missed, because it comes on slowly and is easy to attribute to age alone. Running a structured body condition score every few weeks, and photographing your horse from the same spot each month, will catch it far sooner than eyeballing a horse you see every day.

Advanced Signs of PPID

By the time the following are obvious, the disease has been present for some years and some damage may be irreversible:

Hirsutism, sometimes called hypertrichosis: the long, curly, teddy bear coat that fails to shed at all. This is close to diagnostic on its own
Marked muscle wastage with a pot-bellied silhouette and prominent withers
Severe, often acute laminitis, frequently the reason the vet is called in the first place
Excessive sweating, or less commonly a reduced ability to sweat
Susceptibility to infection: sinus infections, foot abscesses, dental disease, and worm burdens that respond poorly
Infertility in breeding mares
Neurological signs, including blindness, in the rare cases where the enlarged pituitary compresses adjacent structures

How Fast Does Cushing’s Disease Progress?

This is one of the most common questions owners ask after a diagnosis, and the honest answer is that PPID progresses slowly and unevenly. It is measured in years, not weeks. Horses have been documented in a transitional stage, showing subtle signs and equivocal test results, for two to three years before meeting a clear diagnostic threshold.

What that means in practice is more encouraging than it sounds. A single normal ACTH result does not clear a horse for life, so a suspicious pony should be retested rather than written off. Equally, a diagnosis is not a cliff edge. Most horses caught before laminitis has taken hold have years of comfortable life ahead of them, and the speed of decline depends far more on whether laminitis is controlled than on the pituitary itself.

Cushing’s vs Equine Metabolic Syndrome (EMS)

One of the most common questions vets get asked is whether a pony has Cushing’s or Equine Metabolic Syndrome. They are not the same condition, but they overlap heavily: depending on the study, somewhere between one third and two thirds of PPID equids also have insulin dysregulation. A horse can have one, the other, or both.

Feature	PPID (Cushing’s)	EMS
Typical age	15 years and older	Any age, often 5 to 15
Primary fault	Pituitary dysfunction	Insulin dysregulation
Coat changes	Yes: delayed shedding, then hirsutism	No
Muscle loss	Yes, progressive	No, often good doers
Cresty neck and fat pads	Sometimes	Hallmark feature
Laminitis pattern	Recurrent, often year-round	Often pasture-associated. Spring and autumn are flashpoints, but there is no safe season (Pollard et al., 2019)
Diagnostic test	Basal ACTH, or TRH stimulation test	Insulin response, such as an oral sugar test
Treatment	Pergolide, plus diet and foot management	Diet and exercise first, medication in selected cases

PPID and EMS compared. The two frequently coexist, and a horse with both needs the diet of an EMS case and the medication of a PPID case.

If a horse fits the classic EMS profile, meaning middle-aged, native breeding, a good doer with regional fat deposits, but laminitis is becoming recurrent or muscle is now wasting despite weight loss, then retesting for PPID is warranted even if a previous ACTH was normal.

How Vets Diagnose Cushing’s Disease in Horses

Diagnosis rests on two blood tests: a basal ACTH measurement, and, where the result falls in a grey zone, a TRH stimulation test. Both can be run at the yard.

Basal ACTH Test

A jugular blood sample is taken into an EDTA tube and sent chilled to the laboratory. Interpretation has to be seasonally adjusted, because ACTH rises naturally in the autumn. In UK laboratory data, concentrations peak in September and are at their lowest in April (Durham, Potier and Huber, 2022). Those are northern hemisphere months: the Equine Endocrinology Group notes that they need seasonal correction in the southern hemisphere, which includes South Africa.

The Equine Endocrinology Group’s recommendations, revised in October 2025, frame interpretation around an interpretive zone rather than a single threshold, and the zone moves through the year. These are its northern hemisphere figures for baseline ACTH on the Immulite 2000xpi analyser the thresholds are based on:

December to June: below 15 pg/ml PPID is unlikely, 15 to 40 pg/ml is the interpretive zone, where clinical signs and signalment decide, and above 40 pg/ml PPID is likely
July and November: interpretive zone 15 to 50 pg/ml
August: interpretive zone 20 to 75 pg/ml
September and October: interpretive zone 30 to 90 pg/ml
A correction: an earlier version of this page gave 30 to 50 pg/ml outside autumn and 50 to 100 pg/ml in autumn. Those are not the current EEG zones, and under them a result between 15 and 30 pg/ml outside autumn would have looked clear

Two important caveats. First, individual laboratories publish their own seasonally adjusted reference ranges and revise them: Liphook, for example, updates its range on a rolling basis from the very large sample volume it processes. Always interpret against the range printed on your own report, not against a number from an article. Second, breed matters. Donkeys, Shetland ponies, Welsh ponies and Arabians tend to run higher ACTH values, particularly in autumn, while Thoroughbreds, Warmbloods and Connemara ponies tend to run lower. A borderline result in a Thoroughbred may mean more than the same number in an Arabian.

Testing during the autumn rise improves the test’s accuracy: in UK laboratory data the difference between PPID and normal horses was greatest from August to October (Copas and Durham, 2012), and an Australian population study found sensitivity and specificity close to 100% for autumn samples (McGowan et al., 2013). Stress, excitement and travel all raise ACTH transiently and can produce a false positive. The EEG advises against sampling a horse that is visibly excited or within 30 minutes of travelling, and the BHS says a horse that has travelled to the vet may need to rest for at least 30 minutes first. Testing can be done in a laminitic horse, but the EEG says it is ideal to postpone it until severe pain is controlled.

TRH Stimulation Test

For equivocal ACTH results, the TRH (thyrotropin-releasing hormone) stimulation test is the recommended follow-up and the most useful test for early disease. A baseline sample is drawn, TRH is injected intravenously, and a second sample is taken at exactly 10 minutes. A PPID horse shows an exaggerated ACTH rise where a normal horse does not.

The dose is weight-banded, which matters on a native pony yard: 1.0 mg for equids over 250 kg, and 0.5 mg for equids under 250 kg. Plenty of Shetlands, Welsh Section A ponies and small donkeys fall under that 250 kg line.

What About the Dexamethasone Suppression Test?

The overnight dexamethasone suppression test was historically the standard but is now rarely used in the UK, because it carries a small but real risk of triggering laminitis in an at-risk horse. Most practices have moved entirely to ACTH-based testing.

Treatment of Cushing’s in Horses: Pergolide (Prascend)

The only licensed treatment for PPID in the UK and EU is pergolide mesylate. Prascend (Boehringer Ingelheim, 1 mg scored tablets) has been authorised in Great Britain since 2010, but it is not the only brand: the VMD’s Product Information Database also lists Pergoquin 1 mg, Prasequine 1 mg and Pergocoat 0.5 mg, 1 mg and 2 mg tablets as authorised in Great Britain. Pergolide is a dopamine agonist: it replaces the missing dopaminergic suppression at the pituitary and reduces ACTH output. It does not reverse the disease, but it controls the clinical signs and slows progression.

Pergolide Dosing

The licensed starting dose is 2 micrograms per kg bodyweight, once daily by mouth. Because the tablets are scored and dosed to the nearest half tablet, the Prascend product licence sets out the starting dose as a weight band. Other brands use their own bands: the Pergoquin and Prasequine licences give three quarters of a 1 mg tablet (0.75 mg) from 301 to 400 kg, so follow the label of the product your vet dispenses:

Bodyweight	Prascend 1 mg tablets	Starting dose
200 to 400 kg	Half a tablet	0.5 mg
401 to 600 kg	One tablet	1.0 mg
601 to 850 kg	One and a half tablets	1.5 mg
851 to 1000 kg	Two tablets	2.0 mg

Licensed starting doses from the UK Summary of Product Characteristics for Prascend. A 500 kg horse starts on a whole 1 mg tablet, not a half.

Correction to an earlier version of this article. A previous version of this page stated the starting dose as half a tablet for a 500 kg horse and a quarter tablet for a 300 kg pony. Both figures were roughly half the licensed dose and have been corrected above. A 500 kg horse starts on one whole tablet, and a 300 kg pony on a half. If you have been dosing from the old figures, speak to your vet rather than adjusting on your own, because the dose should be changed alongside ACTH monitoring.

Titration: if signs are not controlled, the dose is increased in 0.5 mg steps, reassessed every 4 to 6 weeks with a repeat ACTH
Maintenance: most horses settle somewhere between 0.5 mg and 2 mg per day
Upper end: the UK licence notes some horses need doses as high as 10 micrograms per kg per day. Note that this is a genuine difference between markets: the US label caps dosing at 4 micrograms per kg, so American articles and forum advice will quote a lower ceiling than your UK vet works to

Side Effects and the First Fortnight

The side effect owners actually meet is a loss of appetite and dullness in the first weeks, sometimes called the pergolide veil. The reported frequency depends entirely on how it was measured, and the two figures in circulation are both correct but not comparable. The UK product licence classes inappetence as a rare adverse reaction, which is a pharmacovigilance figure based on spontaneous reports. In the manufacturer’s pre-approval field study, where appetite was actively monitored, 40 of 122 horses, or roughly one in three, showed reduced appetite, and most cases were transient and occurred in the first month.

Practically, expect it, do not panic, and do not stop the drug on your own. The EEG says it is often self-limiting. For persistent inappetence, the strategies its members use are pausing the drug for a few days and restarting at a lower dose, splitting the daily dose into two (an extra-label use, because the licence is for once-daily dosing), or giving it at a different time from the horse’s normal meals. All of these are your vet’s call.

What It Costs in the UK

A box of 60 one milligram Prascend tablets typically runs to somewhere in the region of eighty to a hundred and twenty pounds from a UK veterinary pharmacy with a prescription, so a 500 kg horse on one tablet a day, which gets through a 60-tablet box every two months, sits at roughly forty to sixty pounds a month. Add annual ACTH retesting, plus the call-out. Prices move, and prescription and dispensing arrangements vary between practices, so treat these as an order of magnitude rather than a quote. Generic compounded pergolide is available in some markets but is not licensed in the UK.

Can You Compete a Horse on Pergolide? FEI and UK Rules

This section carried a significant error in the previous version of this article and has been rewritten against the primary source. If you compete, read it carefully, because the position in the UK is not the same as the position in the United States.

Pergolide appears on the FEI Equine Prohibited Substances List as a Controlled Medication, classified as a dopamine agonist. Controlled Medications are substances with a recognised therapeutic use that are nonetheless not permitted to be present in a horse at a competition. They require a withdrawal period before you compete. They are not a free pass.

British Dressage, British Eventing and British Showjumping run their anti-doping rules in alignment with the FEI list, so the same restriction applies at affiliated level in the UK.

The correction. The previous version of this page stated that a horse with a confirmed PPID diagnosis could apply for an Equine Therapeutic Use Exemption and compete on Prascend under FEI or British Dressage rules. That described the American system, not the British one. The Therapeutic Use Exemption that allows a documented PPID horse to remain on pergolide and compete is a USEF provision, introduced in December 2018, and it applies in the United States. UK and FEI competitors do not have an equivalent route, and a horse competing with pergolide in its system at an affiliated or international event is at risk of a positive test.

If you compete and your horse needs pergolide, the conversation to have with your vet is about detection times, withdrawal, and whether competing is realistic for that horse at all. Rules and substance classifications are revised annually, so check the current list for your discipline before you enter rather than relying on this or any other article. The current list is published by the FEI Clean Sport programme.

Diet and Daily Management for a Horse with Cushing’s

Medication on its own is not enough. Day-to-day management of a PPID horse comes down to three things: controlling sugar and starch to prevent laminitis where the horse is also insulin dysregulated, supporting muscle and topline, and staying on top of the secondary problems that come with a weakened immune response. Not every PPID horse needs a restricted diet, and this page previously implied that it did. The Equine Endocrinology Group’s 2025 recommendations say feed should be chosen on body condition and insulin status, that every PPID horse should be assessed for insulin dysregulation, and that a PPID horse with normal insulin regulation on dynamic testing, such as an oral sugar test, does not need a carbohydrate-restricted diet. Many PPID horses are lean or muscle-wasted and benefit from more fat, protein and calories, through good quality senior feeds, pasture grazing, fat supplements or alfalfa-based feeds. The sugar, starch and grazing controls below are for the insulin-dysregulated horse.

Forage: low non-structural carbohydrate hay is the foundation. Later-cut, more mature hay is in general lower in protein and higher in fibre, but it is not reliably lower in sugar (Stang et al., 2023), so the only way to know what you are feeding is to have it analysed. See our guide to the nutrients in hay for what the numbers on an analysis actually mean
Soaking: soaking hay leaches water-soluble carbohydrate, but the amount removed varies widely between batches and is not predictable from soaking time alone. Treat it as a useful risk-reduction step rather than a guarantee, and be aware that soaking also strips minerals and encourages bacterial growth in warm weather
Grazing: strip grazing, grazing muzzles or a track system. Avoid lush spring and autumn pasture
Hard feed: a genuinely low-sugar, low-starch balancer or a feed formulated for laminitics. Dengie Hi-Fi Molasses Free, Spillers Happy Hoof and TopSpec AntiLam are widely used UK options. Read the label rather than the range name, because some senior and fibre feeds carry a molasses coating that makes them a poor fit for a laminitis-prone horse. Avoid mixes containing cereal grains
Protein: do not restrict it. PPID horses lose muscle, and good quality protein supports topline
Vitamin E and selenium: support muscle and immune function, and many UK forages are selenium-deficient
Omega-3: micronised linseed supports skin condition and helps damp down low-grade inflammation

For the underlying principles of building a ration, our horse feeding guide covers how forage, balancer and hard feed fit together.

Foot Care and Laminitis Surveillance

Laminitis is the single biggest threat to a PPID horse, and it is what most often ends their life. Every PPID horse should be on a regular farriery schedule of roughly every five to six weeks. Any footiness, reluctance to turn on a hard surface, or shortened stride deserves immediate veterinary attention rather than a wait-and-see week.

Radiographs taken at the time of diagnosis are worth the money. They give you a baseline against which subtle rotation can be tracked later, and without one you are guessing. Understanding how the hoof is structured makes it much easier to interpret what your vet and farrier are describing.

Dental, Worming and Skin Care

Dental checks more often than for a younger horse. The BHS suggests every nine to 12 months for most horses and says older horses often need more regular checks, so let your vet or equine dental technician set the interval. Older horses lose teeth faster, and a horse that cannot chew long fibre needs a suitable hay replacer
Faecal worm egg counts three to four times a year between spring and autumn, with tapeworm testing twice a year, ideally in spring and autumn, as the BHS testing-led deworming guidance sets out. PPID horses tend to carry higher burdens and respond less well to treatment
Skin and coat: clip as needed through the warmer months if the coat is heavy, groom daily, and treat pastern dermatitis and rain scald promptly rather than waiting to see whether they settle

Can You Ride a Horse with Cushing’s?

Usually yes, and in most cases you should. A well-controlled PPID horse with healthy feet can stay in light or moderate work for years, and continued exercise helps maintain the topline muscle the disease erodes and supports insulin sensitivity in horses that are also insulin-dysregulated.

The limits are set by the feet and by muscle condition, not by the diagnosis itself. Do not ride a horse with active or suspected laminitis. Be realistic about a horse with significant muscle wastage, and build work back gradually. A heavily coated horse will overheat quickly, so clip, and allow much longer to cool out than you would for a healthy horse. If ridden work is no longer appropriate, a retirement livery may be worth considering, and our guide to horse life stages covers what to expect as a horse moves into its senior years.

Prognosis: How Long Do Horses Live with Cushing’s?

Honestly, the published numbers vary a great deal, and anyone quoting you a single confident figure is oversimplifying. One long-term follow-up of equids treated with pergolide reported a median survival of around 3.6 years from the start of treatment, with a range from well under a year to over a decade. Other reports of median life expectancy after diagnosis run closer to nine or ten years. The spread reflects how different these populations are: horses referred to a hospital in crisis are not comparable to ponies picked up early on a routine autumn blood test.

What the evidence does support consistently is the direction of travel. Horses diagnosed and treated before significant laminitis has occurred do considerably better than those diagnosed after repeated laminitic episodes. In that second group, chronic founder, recurrent infection and welfare-driven euthanasia are the usual outcomes. The BHS makes the same point: identifying PPID early means you can start managing it sooner. Test early, treat early, and keep a close watch on the feet and body condition.

Late Stages of Cushing’s and Knowing When to Stop

This is the section nobody wants to read, and it is the one owners search for most at two in the morning. Late-stage PPID is usually characterised by laminitis that no longer responds to treatment, profound muscle loss, repeated infections, and a horse that is visibly uncomfortable rather than simply old.

There is no single test that tells you it is time. Questions worth weighing up include:

Is pain being controlled, and at what cost in medication and side effects?
Can the horse lie down and get back up comfortably?
Is it still doing the things it enjoys: grazing, moving freely, interacting with other horses?
Are the good days still outnumbering the bad, and honestly, is that still true this month?
Is the laminitis stable, or is each episode leaving the horse worse than the one before?

Ask your vet directly for their assessment, and ask early rather than at the point of crisis. A planned decision made at home on a good day is almost always kinder than an emergency one. The BHS’s own line, from its Friends at the End service, is that “It’s better a week too soon than a day too late.”

When to Call the Vet

Phone your vet promptly if your older horse shows any of the following:

A winter coat that has not shed properly by late spring
Unexplained loss of topline muscle
A laminitis episode at any time of year, which is an emergency in its own right
Recurrent skin infections, foot abscesses, or wounds that will not close
A good doer that suddenly stops being one, because weight loss in a senior pony is a red flag

Frequently Asked Questions

What are the first signs of Cushing’s disease in horses?

The earliest signs are subtle: delayed shedding of the winter coat, longer guard hairs under the jaw and behind the legs, loss of topline muscle despite adequate feed, mild lethargy, and regional fat pads such as a cresty neck or fat above the eye. Recurrent low-grade footiness after spring grass is another common early clue. The obvious curly coat is a late sign, not a first one.

What is the life expectancy of a horse with Cushing’s disease?

Published figures vary widely. One long-term study of pergolide-treated equids reported a median survival of around 3.6 years from the start of treatment, with individuals ranging from under a year to more than ten, while other reports of life expectancy after diagnosis run closer to nine or ten years. The strongest predictor is not the diagnosis itself but whether laminitis has already taken hold.

What should you not feed a horse with Cushing’s?

If your horse is also insulin dysregulated, avoid cereal grains, sweet feeds, molasses, and any feed marketed as conditioning or competition that is built on oats, barley or maize. Treat carrots and apples as occasional, not daily. Lush spring and autumn grazing needs restricting. Check labels rather than trusting a product range name, since some senior fibre feeds carry a molasses coating. A PPID horse with normal insulin regulation on dynamic testing does not need a carbohydrate-restricted diet, according to the Equine Endocrinology Group, and many lean PPID horses benefit from more calories rather than fewer.

How much does pergolide cost in the UK?

Prascend is dispensed as 1 mg tablets on prescription, typically in boxes of 60, and a 500 kg horse on one tablet a day generally works out at somewhere around forty to sixty pounds a month. Budget additionally for annual ACTH retesting and the associated call-out. Prices vary between practices and change over time, so ask your own vet for a current figure.

Can you compete a horse on Prascend in the UK?

Not without a withdrawal period. Pergolide is listed as a Controlled Medication on the FEI Equine Prohibited Substances List, and British Dressage, British Eventing and British Showjumping align with that list. The Therapeutic Use Exemption that lets a documented PPID horse compete while on pergolide is a USEF provision that applies in the United States, not in the UK. Discuss detection times with your vet and check the current list for your discipline before entering.

Can Cushing’s disease in horses be cured?

No. PPID is caused by progressive degeneration of dopamine-producing neurones and cannot be reversed. Pergolide controls the signs, slows progression and substantially reduces laminitis risk, but treatment is lifelong.

Is Cushing’s the same as Equine Metabolic Syndrome?

No. PPID is a pituitary disorder of older horses driven by dopaminergic neurodegeneration, whereas EMS is an insulin-dysregulation disorder typically seen in middle-aged native breeds. They frequently coexist, with somewhere between a third and two thirds of PPID equids also showing insulin dysregulation, and the diagnostic and management approaches differ.

When is the best time of year to test for Cushing’s?

Testing during the autumn rise, when ACTH concentrations peak around September in the northern hemisphere (southern hemisphere months need seasonal correction), gives the best sensitivity for picking up early cases, and laboratories apply higher seasonally adjusted reference ranges to account for it. For horses already diagnosed and being monitored on pergolide, retest at the same time each year so you are comparing like with like.