Can Hair Samples Diagnose Cushing’s Disease in Horses?
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Can Hair Samples Diagnose Cushing’s Disease in Horses?
By Dr Duncan Houston
Hair changes can strongly suggest PPID, but hair sample testing is not currently a reliable standalone way to diagnose Cushing’s disease in horses.
Equine Cushing’s disease is more accurately called pituitary pars intermedia dysfunction, or PPID. It is one of the most common endocrine diseases in older horses, ponies, and donkeys. The classic sign is a long, curly, delayed-shedding coat, but PPID is much bigger than hair. It can affect muscle, hooves, immunity, wound healing, drinking, urination, energy, sweating, and laminitis risk.
Recently, there has been interest in whether hair samples, especially hair cortisol testing, could help identify PPID. That sounds attractive because hair collection is easy, non-invasive, and less stressful than blood collection. But the important clinical answer is this: hair sample testing is still not a standard diagnostic test for PPID.
At the moment, the most practical diagnostic approach remains veterinary assessment combined with blood testing, especially baseline ACTH and, where appropriate, TRH stimulation testing. The 2025 Equine Endocrinology Group recommendations state that documentation of increased plasma ACTH at rest and/or after TRH stimulation is currently the most practical diagnostic test for PPID, interpreted alongside season, breed, clinical signs, and the individual horse’s health context. (Squarespace)
Quick Answer
Hair samples cannot currently replace blood testing for diagnosing PPID in horses. Hair coat changes such as hypertrichosis, delayed shedding, and retained long hairs can strongly raise suspicion for PPID, but hair cortisol testing remains experimental or research-adjacent rather than a routine clinical diagnostic test. Current diagnosis relies mainly on clinical signs, baseline ACTH testing, TRH stimulation testing, and insulin assessment when laminitis risk is a concern. (Squarespace)
What Is PPID in Horses?
PPID is a slowly progressive, age-related degenerative disease affecting dopamine control of the pars intermedia of the pituitary gland. As dopamine inhibition is lost, the pars intermedia becomes overactive and releases increased ACTH and related peptides. The condition becomes more common with age, with current guidance reporting prevalence around 20 percent in equids over 15 years and around 30 percent in equids over 30 years. (Squarespace)
Common signs include:
| Sign | Why it matters |
|---|---|
| Long curly coat | Classic PPID sign |
| Delayed shedding | Often one of the earliest visible clues |
| Patchy retained guard hairs | May appear before the whole coat changes |
| Muscle loss along the topline | Common in older PPID horses |
| Rounded abdomen | Often linked with muscle loss |
| Increased drinking and urination | Can occur with PPID or other disease |
| Abnormal sweating | May be increased or reduced |
| Recurrent infections | Poor immune resilience may be involved |
| Poor wound healing | Important monitoring clue |
| Laminitis | One of the most serious complications |
| Recurrent corneal ulcers | Listed in the clinical spectrum of PPID |
The Equine Endocrinology Group lists hypertrichosis, delayed shedding, muscle loss, recurrent infections, poor wound healing, recurrent corneal ulcers, insulin dysregulation, and hyperinsulinemia-associated laminitis within the clinical spectrum of PPID. (Squarespace)
Can Hair Samples Diagnose PPID?
Not reliably at this stage.
Hair is useful in two very different ways, and owners should not confuse them.
| Hair-related clue | What it means |
|---|---|
| Hair coat changes | A clinical sign that may strongly suggest PPID |
| Hair cortisol testing | A possible research tool, not a routine diagnostic replacement for ACTH or TRH testing |
A long, curly, delayed-shedding coat can be a powerful clinical clue, especially in an older horse. In advanced cases, the appearance may be so typical that a vet may make a clinical diagnosis, particularly when testing is unavailable or the clinical signs are severe. The 2025 EEG diagnostic algorithm notes that in aged horses with advanced clinical signs, a clinical diagnosis without testing may also be made. (Squarespace)
Hair cortisol testing is different. It is not the same as looking at the coat. It involves measuring cortisol accumulation in hair. Research has shown some differences between PPID and control horses in certain seasons, but the results are too variable to use hair cortisol alone as a dependable diagnostic test. (ScienceDirect)
Why Hair Cortisol Testing Sounds Appealing
Hair cortisol is interesting because hair can reflect hormone exposure over a longer period than a single blood sample. A blood result is a snapshot. Hair may act more like a longer-term record.
In theory, that could make hair attractive for a chronic endocrine disease such as PPID. A horse owner would love a simple, non-invasive test where you trim a small patch of hair, send it to a lab, and get a clear answer.
The problem is that biology is rarely that tidy. Very rude of biology, honestly.
A 2020 study found that hair cortisol was higher in PPID horses than controls in late fall, but it was similar in spring, early fall, and across different sampling sites in spring. The same study found no consistent relationship between ACTH and hair cortisol concentrations, and concluded that hair cortisol alone is currently unlikely to be a useful indicator of PPID. (ScienceDirect)
That is the key point. Interesting does not yet mean clinically dependable.
Why Hair Samples Are Not Enough
A PPID diagnosis has consequences. It may mean lifelong medication, ongoing monitoring, laminitis prevention, insulin testing, diet changes, farrier planning, and repeated veterinary review.
That is why the test needs to be clinically useful, not just convenient.
Hair cortisol is limited because:
| Limitation | Why it matters |
|---|---|
| Seasonal variation | Hair cortisol differences may appear in some seasons but not others |
| Hair growth differences | Hair length and growth rate affect interpretation |
| Sampling site variation | Different body areas may not behave identically |
| Weak relationship with ACTH | Hair cortisol may not track the main blood marker used for PPID diagnosis |
| No routine clinical thresholds | There are no widely accepted cut-offs for diagnosing PPID from hair cortisol |
| PPID is not simply high cortisol | Equine PPID is driven by pars intermedia dysfunction and ACTH-related peptide changes, not just classic sustained cortisol excess |
The safest interpretation is this: hair cortisol testing may become more useful in the future, but it should not currently replace a proper PPID workup.
What Tests Are Used To Diagnose PPID?
The most commonly used tests are blood-based.
Cornell lists the commonly used tests for PPID diagnosis and monitoring as baseline endogenous ACTH with insulin, TRH-response ACTH testing, and dexamethasone suppression testing. Post-treatment monitoring may include clinical signs plus ACTH and/or insulin testing. (Cornell Vet College)
The main diagnostic options are:
| Test | What it does |
|---|---|
| Baseline ACTH | Measures resting ACTH from an EDTA plasma sample |
| TRH stimulation test | Measures ACTH response after TRH administration |
| ACTH plus insulin | Helps assess PPID and laminitis risk together |
| Dexamethasone suppression test | Older evocative test, less commonly used in some settings |
| Clinical diagnosis | May be reasonable in aged horses with advanced classic signs |
The 2025 EEG guidance says testing should be interpreted with clinical context, including age, signs, comorbidities, intended use, and season. It also notes that PPID testing is not recommended in the absence of clinical signs. (Squarespace)
Why Season Matters
ACTH changes naturally through the year. This makes seasonal interpretation essential.
The EEG guidance emphasises that season and breed affect ACTH concentrations. It also notes that the specific month ranges in the table are for the northern hemisphere and require seasonal correction for southern hemisphere interpretation. That matters for owners and vets in Australia, New Zealand, South Africa, and other southern hemisphere regions. (Squarespace)
In practical terms, you should not interpret ACTH as a naked number. A result needs context.
Useful context includes:
| Context | Why it matters |
|---|---|
| Season | ACTH rises seasonally |
| Hemisphere | Month-based ranges must be seasonally corrected |
| Breed | Some breeds may have higher values |
| Age | PPID likelihood increases with age |
| Clinical signs | Signs change how strongly a result supports diagnosis |
| Stress or illness | May influence endocrine results |
| Lab method | Reference ranges may vary by assay |
This is exactly why a vet-led interpretation matters.
What About Lipofuscin and Oxidative Stress?
Some discussions around PPID mention lipofuscin, oxidative stress, and neurodegeneration. These are research-level concepts that may help explain disease development, but they should not be turned into owner-facing diagnostic claims.
PPID is associated with neurodegenerative changes affecting dopamine control of the pituitary pars intermedia. The University of Minnesota describes PPID as primarily due to a neurodegenerative process involving loss of hypothalamic neurons, decreased dopamine levels, and increased growth of the pituitary pars intermedia. (College of Veterinary Medicine)
That does not mean hair samples can diagnose organ damage, liver dysfunction, heart fibrosis, or lung disease in a horse with PPID. Those claims need to be handled very carefully. If an individual horse has signs of systemic disease, the answer is not a hair test. The answer is a proper veterinary examination and targeted diagnostics.
Hair Coat Changes That Should Raise Suspicion
Hair sample testing is not yet a standard diagnostic test, but hair coat changes remain one of the most important visible clues.
Watch for:
| Coat sign | Why it matters |
|---|---|
| Long curly coat | Classic advanced PPID sign |
| Delayed shedding | Common early or moderate sign |
| Long hairs under the throatlatch | May be an early clue |
| Retained long hairs on legs | Can be an early or subtle sign |
| Patchy shedding | May occur in PPID |
| Hair colour changes | Listed among PPID-associated clinical changes |
| Abnormal sweating under a heavy coat | Can affect comfort and heat tolerance |
UC Davis lists long curly hair coat, delayed shedding, loss of muscle, abnormal thirst, excessive urination, lethargy, laminitis, chronic infections, decreased wound healing, and higher parasite burdens among recognised PPID signs. (Center for Equine Health)
How Worried Should You Be?
| Risk level | What it looks like | What it may mean | What to do |
|---|---|---|---|
| Low concern | Older horse sheds normally, normal body condition, no laminitis signs, no abnormal thirst or infections | PPID less likely right now | Continue routine monitoring |
| Moderate concern | Delayed shedding, mild patchy coat retention, subtle topline loss, reduced energy | Early PPID or ageing-related change | Book a vet review and discuss ACTH testing |
| High concern | Long curly coat, clear muscle loss, increased drinking, recurrent infections, poor wound healing, abnormal sweating | PPID is more likely | Arrange veterinary testing and insulin assessment |
| Critical | Foot pain, heat in the feet, strong digital pulses, reluctance to move, severe infection, not eating, severe eye pain, or colic signs | Possible laminitis or urgent complication | Call your vet urgently |
The biggest emergency risk is not the hair coat. It is laminitis.
Why Insulin Testing Matters Too
PPID is often accompanied by insulin dysregulation, and insulin status is one of the most important factors for laminitis risk. The 2025 EEG guidance states that insulin dynamics should be assessed in concert with PPID testing. (Squarespace)
UC Davis reports that approximately 30 percent of horses with PPID also show signs of insulin dysregulation, and that knowing insulin status is important for assessing laminitis risk and guiding diet. (Center for Equine Health)
That means a good PPID workup should not stop at ACTH.
It should ask:
| Question | Why it matters |
|---|---|
| Does this horse have PPID? | Guides pergolide and monitoring |
| Does this horse have insulin dysregulation? | Guides laminitis prevention |
| Is the horse overweight or underweight? | Guides diet |
| Has the horse had laminitis before? | Changes urgency |
| Are the hooves already showing chronic change? | May need radiographs and farrier planning |
| Are there infections or poor wound healing? | Suggests control or wellness issues |
What Else Can Look Like PPID?
Not every older horse with a poor coat has PPID.
Important rule-outs include:
| Condition | Why it can look similar |
|---|---|
| Normal ageing | Can cause slower shedding, muscle loss, and reduced performance |
| Dental disease | Can cause weight loss and poor condition |
| Parasite burden | Can cause poor coat and weight loss |
| Poor nutrition | Can affect coat, muscle, and energy |
| Chronic pain | Can reduce muscle and performance |
| Liver or kidney disease | Can cause weight loss, dullness, and drinking changes |
| Chronic infection | Can cause poor condition and lethargy |
| Equine metabolic syndrome | Can overlap with PPID and laminitis risk |
| True thyroid disease | Rare in adult horses, but commonly over-suspected |
The real clinical question is not “does my horse have a weird coat?”
It is: what is causing the coat change, and is there laminitis risk?
When Is This an Emergency?
PPID diagnosis is usually not a same-hour emergency. PPID complications can be.
Call your vet urgently if your horse has:
| Red flag | Why it matters |
|---|---|
| Heat in the feet | Possible laminitis |
| Strong digital pulses | Major laminitis warning sign |
| Reluctance to move | Foot pain until proven otherwise |
| Shifting weight | Common laminitis behaviour |
| Rocked-back stance | Serious front foot pain concern |
| Severe infection | PPID horses can have reduced immune resilience |
| Wound that becomes hot, swollen, painful, or draining | Infection risk |
| Eye pain, squinting, or cloudiness | Horse eyes can worsen quickly |
| Not eating after pergolide or dose change | Medication issue or illness |
| Colic signs | Needs urgent assessment |
| Collapse or inability to rise | Emergency |
A long coat can wait for a planned appointment. A PPID horse with sore feet cannot.
What Should You Do Right Now?
1. Do not rely on hair testing alone
Hair cortisol testing is not currently a dependable standalone PPID diagnostic test. Use it only if your vet is specifically recommending it as part of a research or specialist context.
2. Photograph the coat
Take photos of the whole horse, legs, neck, throatlatch, belly, and topline. Repeat monthly during shedding season.
3. Track shedding
Write down when shedding starts, whether it is patchy, and whether long hairs remain after other horses have shed out.
4. Check for laminitis signs
Look for foot soreness, heat, strong digital pulses, reluctance to turn, hoof rings, widened white line, or a rocked-back stance.
5. Ask your vet about ACTH testing
Baseline ACTH is a common starting point, but it must be interpreted with season, clinical signs, breed, and lab method.
6. Ask whether TRH stimulation is needed
TRH stimulation may be helpful when early PPID is suspected or baseline ACTH is equivocal.
7. Test insulin where relevant
Especially if the horse has laminitis, a cresty neck, abnormal fat deposits, PPID suspicion, previous founder, or pasture sensitivity.
8. Review the whole horse
Do not focus only on the coat. Review teeth, diet, body condition, hooves, infections, wounds, parasites, pain, and quality of life.
How Is PPID Treated and Monitored?
Pergolide mesylate is the main medication used to treat PPID. The 2025 EEG guidance lists daily oral pergolide as the mainstay of treatment, combined with appropriate dietary management and general wellness care. It recommends evaluating clinical signs with or without endocrine testing 1 to 3 months after starting treatment, then every 6 to 12 months. (Squarespace)
Treatment monitoring should include:
| Monitoring point | Why it matters |
|---|---|
| Coat shedding | Visible response to treatment |
| Appetite | Pergolide can affect appetite in some horses |
| Energy and attitude | Quality of life marker |
| Body condition | PPID horses can be overweight or underweight |
| Muscle mass | Topline loss may persist or worsen |
| ACTH | Helps monitor endocrine control |
| Insulin | Helps assess laminitis risk |
| Hoof health | Early laminitis detection |
| Dental care | Older horses often need feeding support |
| Infections and wound healing | Poor control or ageing issues may be involved |
The EEG guidance also notes that clinical improvement is the most important indicator of response, and ACTH may not return to the “PPID unlikely” range despite clinical improvement. (Squarespace)
Diet: Not Every PPID Horse Needs the Same Plan
This is a big one.
A PPID horse with high insulin and laminitis risk needs a very different diet from a thin older horse with PPID, muscle loss, poor teeth, and normal insulin regulation.
The 2025 EEG guidance states that feed selection in PPID horses should be based on body condition and whether insulin dysregulation is present. Horses with PPID and insulin dysregulation require lower non-structural carbohydrate feeds and limited pasture access, but PPID horses with normal insulin regulation confirmed by dynamic testing do not automatically need a carbohydrate-restricted diet. (Squarespace)
| PPID horse type | Diet focus |
|---|---|
| Overweight with high insulin | Low NSC forage, pasture restriction, controlled calories |
| Lean with normal insulin | Adequate calories, quality protein, senior feed support |
| Poor teeth | Soaked feeds, chopped forage, dental-friendly nutrition |
| Previous laminitis | Strict insulin and pasture management |
| Muscle wasting | Protein, calories, pain control, dental review, PPID treatment |
The mistake is feeding every PPID horse like a fat pony. Some are. Some are not.
Common Mistakes Owners Make
Mistake 1: Thinking hair samples replace blood testing
They do not. Hair cortisol is interesting, but current evidence does not support it as a standalone diagnostic test.
Mistake 2: Ignoring coat changes because the horse is “just old”
Delayed shedding, retained long hairs, and a long curly coat are important clues in older horses.
Mistake 3: Testing ACTH but forgetting insulin
ACTH helps assess PPID. Insulin helps assess laminitis risk. Many horses need both.
Mistake 4: Treating the number, not the horse
ACTH must be interpreted with clinical signs, season, breed, comorbidities, and response to treatment.
Mistake 5: Starving a thin PPID horse
Lean PPID horses may need more nutrition, not less. Diet depends on insulin status and body condition.
Mistake 6: Waiting until laminitis is obvious
Subtle foot soreness, hoof rings, stronger digital pulses, or reluctance to turn may be early warning signs.
Prevention and Long-Term Monitoring
You cannot prevent every case of PPID, but you can detect it earlier and reduce complications.
| Monitoring step | Why it helps |
|---|---|
| Check coat shedding each season | Detects early visible changes |
| Body condition score monthly | Tracks weight gain or loss |
| Watch topline muscle | Muscle loss is common in PPID |
| Test ACTH when signs suggest PPID | Supports diagnosis and monitoring |
| Test insulin in at-risk horses | Protects against laminitis risk |
| Schedule regular farrier care | Detects chronic hoof change |
| Keep dental care current | Older horses need safe nutrition |
| Monitor infections and wounds | Poor healing may suggest control issues |
| Track appetite and attitude | Quality of life matters |
| Review diet regularly | Feed needs change with age and insulin status |
The best PPID monitoring plan is not dramatic. It is consistent.
Myth vs Reality
| Myth | Reality |
|---|---|
| “Hair samples can diagnose PPID now.” | Hair cortisol testing is not currently a reliable standalone PPID diagnostic test. |
| “A long coat always means PPID.” | It is highly suspicious in older horses, but the full clinical picture still matters. |
| “A normal ACTH always rules PPID out.” | Early PPID can be difficult to diagnose, and repeat or dynamic testing may be needed. |
| “PPID is only a coat problem.” | Laminitis, insulin dysregulation, infections, wound healing, muscle loss, and quality of life matter more. |
| “Every PPID horse needs a low-carb diet.” | Only if insulin dysregulation or laminitis risk requires it. |
| “Pergolide fixes everything.” | Pergolide helps PPID, but hoof care, diet, insulin testing, dentistry, and monitoring still matter. |
Will My Horse Be Okay?
Many horses with PPID live comfortably for years with good management.
The outlook is better when:
| Good sign | Why it helps |
|---|---|
| PPID is recognised early | Treatment and monitoring can start before severe complications |
| Insulin is checked | Laminitis risk becomes clearer |
| Pergolide response is monitored | Dose and management can be adjusted |
| Hoof care is regular | Laminitis changes are caught earlier |
| Diet matches the horse | Prevents both overfeeding and underfeeding |
| Infections are treated quickly | Reduces complications |
| Owner tracks changes over time | Patterns become easier to see |
The outlook becomes more guarded when there is repeated laminitis, uncontrolled insulin, severe weight loss, recurrent infections, poor appetite, severe dental disease, or delayed veterinary care.
Related Horse Health Topics To Link Internally
| Related topic | Why it connects |
|---|---|
| How To Monitor Cushing’s Disease in Horses | PPID needs ongoing tracking |
| How To Prevent Founder in Horses | Laminitis is one of the biggest PPID risks |
| Hyperinsulinemia in Horses | High insulin drives laminitis risk |
| Insulin Response in Older Horses | Senior horses may need closer metabolic monitoring |
| Thyroid Supplements for Horses | Often confused with endocrine and weight management |
| Corneal Ulcers in Horses With PPID | PPID and ageing may affect corneal health |
FAQs About Hair Samples and PPID in Horses
Can a hair sample diagnose Cushing’s disease in horses?
Not reliably at this stage. Hair cortisol testing has been studied, but current evidence does not support it as a standalone diagnostic test for PPID.
What is the best test for PPID in horses?
The most practical tests are baseline ACTH and, where appropriate, TRH stimulation testing. Results should be interpreted with season, clinical signs, breed, age, and overall health context. (Squarespace)
Is a long curly coat enough to diagnose PPID?
In an older horse with advanced classic signs, a vet may make a clinical diagnosis, especially if testing is unavailable. For mild or early cases, blood testing is usually needed.
Why does insulin need to be tested in PPID horses?
Because PPID is often accompanied by insulin dysregulation, and high insulin increases laminitis risk. Diet and pasture recommendations depend heavily on insulin status. (Squarespace)
Should I ask my vet for hair cortisol testing?
You can ask, but it is not currently a routine replacement for ACTH or TRH testing. It is better to ask your vet for a full PPID and insulin risk assessment.
The Bottom Line
Hair can tell you a lot about a horse with PPID, but not in the way many people think.
A long, curly, delayed-shedding coat is one of the most important visible warning signs of Cushing’s disease in horses. But hair sample testing, especially hair cortisol testing, is not currently reliable enough to replace proper veterinary diagnosis.
The safest approach is simple: use coat changes as a reason to investigate, not as the whole diagnosis. If your older horse is not shedding normally, losing topline, drinking more, developing infections, healing slowly, or showing any foot soreness, speak to your vet about ACTH testing, TRH stimulation where appropriate, insulin testing, and laminitis prevention.
Hair may raise the alarm. Bloodwork, clinical judgement, insulin assessment, and ongoing monitoring guide the plan.
If you are unsure whether your horse’s coat changes, hoof soreness, weight loss, infections, or drinking changes could be PPID, ASK A VET™ can help you understand what signs matter and when veterinary care is needed.