Understanding Cushing’s Disease in Horses: A Comprehensive Guide to PPID

What is Cushing’s Disease?

Cushing’s disease in horses, more accurately termed Pituitary Pars Intermedia Dysfunction (PPID), is a common endocrine (hormonal) disorder primarily affecting older horses. This progressive condition results from dysfunction of the pituitary gland—a small but critically important structure located at the base of the brain that regulates numerous hormonal systems throughout the body. When the pituitary gland malfunctions in PPID, it produces excessive amounts of several hormones, leading to a wide array of clinical signs and significantly increased risk of serious complications including laminitis.

The pituitary gland consists of three distinct regions: the anterior lobe (pars distalis), the intermediate lobe (pars intermedia), and the posterior lobe (pars nervosa). In horses with PPID, the pars intermedia undergoes abnormal changes including enlargement (hyperplasia) and sometimes development of benign tumors (adenomas). These changes cause the pars intermedia to produce excessive quantities of various peptide hormones, most notably adrenocorticotropic hormone (ACTH) and related compounds.

ACTH stimulates the adrenal glands (small organs located near the kidneys) to produce cortisol—often called the “stress hormone.” Elevated cortisol levels affect virtually every system in the body, contributing to many of the clinical signs horses with PPID display. However, PPID involves more than just cortisol excess; the dysfunction produces multiple hormonal imbalances that collectively create the syndrome we recognize as Cushing’s disease.

PPID represents one of the most common endocrine disorders in horses, with prevalence increasing dramatically with age. Studies suggest that 20-30% or more of horses over 15 years old may be affected, and prevalence continues rising with advancing age—some estimates suggest up to 50% of horses over 25 years may have the condition. All breeds can develop PPID, though Morgan horses and ponies may show somewhat higher susceptibility.

Understanding PPID is essential for anyone caring for older horses, as early diagnosis and treatment can dramatically improve quality of life, prevent serious complications, and potentially extend horses’ healthy lifespan. Left untreated, PPID causes progressive deterioration, increased susceptibility to infections, metabolic derangements, and potentially fatal complications including severe laminitis.

The Pituitary Gland and Its Normal Function

To understand what goes wrong in PPID, we must first comprehend the normal anatomy and function of the equine pituitary gland and its regulatory mechanisms.

The pituitary gland (also called the hypophysis) sits in a small bony cavity called the sella turcica at the base of the brain, connected to the hypothalamus (a brain region that regulates many automatic body functions) by a thin stalk. Despite its small size—roughly the size of a grape in horses—the pituitary serves as the body’s “master gland,” secreting hormones that regulate growth, metabolism, reproduction, stress responses, and numerous other critical functions.

The pars intermedia (intermediate lobe), the region affected in PPID, produces several related peptide hormones derived from a common precursor molecule called pro-opiomelanocortin (POMC). This precursor is enzymatically cleaved into multiple active hormones including:

ACTH (adrenocorticotropic hormone): Stimulates cortisol production by the adrenal glands
α-MSH (alpha-melanocyte stimulating hormone): Influences pigmentation and other functions
β-endorphin: An endogenous opioid involved in pain modulation
CLIP (corticotropin-like intermediate peptide): Functions incompletely understood

In healthy horses, the pars intermedia is under inhibitory control by the hypothalamus through a neurotransmitter called dopamine. Dopamine-producing nerve cells in the hypothalamus extend down through the pituitary stalk and release dopamine directly onto pars intermedia cells, suppressing their activity and hormone production. This dopaminergic inhibition keeps pars intermedia hormone secretion at appropriate levels.

The system functions as a negative feedback loop: when circulating cortisol levels are adequate, the hypothalamus maintains dopamine release, suppressing ACTH production. If cortisol levels drop (during stress, for example), the hypothalamus adjusts, allowing increased ACTH secretion to stimulate more cortisol production. This elegant regulatory system maintains hormonal balance under varying conditions.

What Goes Wrong in PPID

In horses with PPID, this carefully regulated system breaks down through a complex pathological process that remains incompletely understood but appears to involve:

Loss of dopaminergic neurons: The dopamine-producing nerve cells that normally inhibit the pars intermedia progressively degenerate and die. The cause of this neurodegeneration remains unclear but may involve:

Oxidative stress and free radical damage accumulating with age
Mitochondrial dysfunction within neurons
Possible inflammatory processes
Genetic susceptibility factors
Other age-related degenerative changes

As dopaminergic neurons are lost, inhibitory control over the pars intermedia fails. Without adequate dopamine suppression, the pars intermedia cells become hyperactive, proliferating and producing excessive quantities of POMC-derived hormones.

The pars intermedia undergoes hyperplasia (increased cell numbers) and may develop adenomas (benign tumors). While these growths are not malignant and don’t metastasize, they can become quite large, sometimes compressing adjacent brain structures and producing neurological signs in advanced cases.

The excessive hormone production that results includes:

Elevated ACTH: Chronic overproduction of ACTH stimulates the adrenal glands to produce excessive cortisol. This hypercortisolemia (elevated blood cortisol) creates many of PPID’s clinical signs and complications. However, cortisol levels in PPID are often only mildly to moderately elevated—not as dramatically high as in some other forms of Cushing’s syndrome—and may even be within normal ranges at times, yet still contribute to problems.

Other POMC-derived peptides: Excessive production of α-MSH, β-endorphin, CLIP, and other peptides may contribute to clinical signs through mechanisms that remain incompletely understood.

The progressive nature of PPID means that horses typically show subtle early signs that gradually worsen over months to years as the pituitary dysfunction advances. Understanding this progression helps explain why early detection and treatment intervention proves so beneficial.

Clinical Signs and Symptoms

PPID produces a characteristic constellation of clinical signs, though not every affected horse displays all possible symptoms. The severity and specific combination of signs vary among individuals and typically worsen as the disease progresses.

Hirsutism (Abnormal Hair Coat)

Hirsutism—the development of an abnormally long, thick, curly hair coat that fails to shed normally—represents the most pathognomonic (characteristic and diagnostic) sign of PPID. This distinctive coat change results from hormonal effects on hair follicles and hair growth cycles.

Affected horses develop:

Long, wavy, or curly hair coat that may grow several inches long, particularly along the jaw, neck, and legs
Failure to shed properly in spring and summer, retaining the winter coat partially or completely
Coat color changes: Sometimes horses develop lighter or grizzled coats
In severe cases, the coat becomes so long and thick it resembles sheep’s wool

The hirsutism typically develops gradually, with early cases showing just delayed shedding or slightly longer hair in certain areas (particularly the jaw and lower legs). As PPID progresses, the coat abnormality becomes more pronounced and obvious.

Importantly, not all horses with PPID develop obvious hirsutism, particularly in early disease stages. Some horses may show other signs of PPID for months or even years before coat changes become apparent. Conversely, advanced hirsutism indicates moderate to severe PPID that has been present for some time.

Laminitis

Laminitis represents the most serious complication of PPID and a leading cause of euthanasia in affected horses. Horses with PPID face dramatically increased laminitis risk—studies suggest 30-50% or more of PPID horses will experience at least one laminitic episode.

The mechanism linking PPID to laminitis involves:

Insulin dysregulation: Many PPID horses develop insulin resistance and hyperinsulinemia (elevated insulin levels), which directly damages laminar tissues
Altered glucose metabolism: PPID affects how the body processes carbohydrates
Immune suppression: Increased infection susceptibility may trigger laminitis
Direct hormonal effects: Cortisol and other hormones may affect hoof tissues
Altered blood flow: Hormonal changes may affect circulation to the hoof

PPID-associated laminitis may be acute and severe or chronic and low-grade. Some horses experience recurring acute episodes, while others have persistent, smoldering laminar inflammation that gradually worsens hoof structure over time.

Prevention of laminitis represents a primary goal of PPID management and one of the most important reasons for early diagnosis and treatment.

Muscle Wasting and Altered Body Condition

PPID horses typically develop distinctive changes in muscle mass and body composition:

Muscle atrophy (loss of muscle tissue) particularly affects:

Topline: Loss of muscling along the back and croup, creating a “sway-backed” appearance
Hindquarters: Prominent hip bones and atrophied gluteal muscles
Temporal muscles: Hollows above the eyes from muscle loss in the temporalis muscles
Overall loss of muscle tone despite adequate nutrition

Redistribution of body fat creates an unusual appearance:

Pot-bellied appearance: Enlarged, pendulous abdomen
Fat deposits: Abnormal fat accumulation along the crest of the neck, above the eyes (supraorbital fat pads), in the sheath (males), or mammary region (females)
Overall body condition: Horses may appear thin in muscled areas while having areas of abnormal fat deposition

This altered body composition—loss of muscle with pot-bellied appearance and abnormal fat distribution—creates a characteristic appearance that experienced horsemen often recognize immediately.

Increased Drinking and Urination (PU/PD)

Many PPID horses develop polyuria (increased urination) and polydipsia (increased drinking). Owners may notice:

Constantly wet stalls requiring more frequent bedding changes
Horses spending excessive time drinking
Water buckets emptying much more quickly than normal
Urine appearing dilute (pale, almost colorless)

This PU/PD results from hormonal effects on kidney function, impairing the kidneys’ ability to concentrate urine. While not dangerous itself, PU/PD creates management challenges and often represents an early sign owners notice before more obvious symptoms develop.

Increased Susceptibility to Infections

Immune suppression from elevated cortisol and other hormonal changes makes PPID horses more vulnerable to infections:

Skin infections:

Dermatophilosis (“rain rot”): Bacterial skin infection causing crusty lesions, particularly common in PPID horses
Dermatophytosis (ringworm): Fungal skin infections
Bacterial folliculitis: Infection of hair follicles
Poor wound healing: Cuts and abrasions heal slowly and may become infected

Respiratory infections:

Increased frequency and severity of respiratory diseases
Slower recovery from respiratory illnesses

Hoof abscesses:

More frequent subsolar abscesses
Slow healing of hoof infections

Dental infections:

Increased periodontal disease
Tooth root infections

Sinus infections, eye infections, and other bacterial or fungal infections occur more commonly in PPID horses due to compromised immune function.

Lethargy and Depression

Many PPID horses demonstrate behavioral changes including:

Decreased energy and alertness
Reduced interest in surroundings
Depression or dullness
Less enthusiasm for work or interaction
Increased time spent resting or sleeping

These changes often develop gradually, and owners may not recognize them as abnormal, attributing the changes to “normal aging.” However, many horses show dramatic improvement in attitude and energy after PPID treatment begins, revealing that the lethargy was disease-related rather than inevitable aging.

Reproductive Problems

Mares with PPID may experience:

Irregular estrous cycles or persistent anestrus (failure to cycle)
Difficulty becoming pregnant
Increased pregnancy loss
Lactation problems

Stallions may show:

Decreased libido
Reduced fertility

Delayed Shedding and Sweating Abnormalities

Beyond frank hirsutism, horses may show:

Delayed shedding in spring
Patchy shedding creating an unkempt appearance
Anhidrosis (inability to sweat normally) in some horses
Hyperhidrosis (excessive sweating) in others

Neurological Signs (Advanced Cases)

When pituitary tumors become very large, they may compress adjacent brain structures, producing neurological signs:

Head pressing
Abnormal mentation or behavior
Visual deficits from optic nerve compression
Seizures (rare)
Other central nervous system signs

These neurological complications indicate advanced disease with large pituitary masses.

Other Signs

Additional clinical findings may include:

Loss of appetite or changes in eating behavior
Weight loss despite adequate feed intake
Tooth problems beyond those expected for age
Delayed shedding of other tissues: Some horses retain caps (baby teeth) longer than normal
Infertility
Chronic colic episodes
Sinusitis

Diagnosis of PPID

Diagnosing PPID requires combining clinical findings with laboratory testing, as clinical signs alone may be subtle in early disease or mimic normal aging changes.

Clinical Examination

A thorough physical examination assesses:

Hair coat quality and shedding pattern
Body condition and muscle development
Signs of laminitis (increased digital pulses, hoof tester sensitivity, gait changes)
Evidence of infections or poor wound healing
Overall demeanor and energy level

The history provides important information about timeline of changes, seasonal patterns, previous laminitis episodes, and response to environmental factors.

Diagnostic Testing

Several laboratory tests help diagnose PPID:

Baseline (Resting) ACTH Measurement

Measuring ACTH concentration in blood plasma represents the most commonly used diagnostic test:

Procedure: A single blood sample is collected and submitted to a laboratory for ACTH measurement using specialized assays.

Interpretation:

ACTH levels above reference ranges support PPID diagnosis
However, reference ranges vary seasonally—ACTH naturally increases in late summer and fall (August-October in the Northern Hemisphere), so different reference ranges apply for different times of year
False negatives occur, particularly in early disease when ACTH may be only intermittently or mildly elevated
False positives are less common but possible, particularly during the fall rise period

Advantages:

Simple, requiring only one blood sample
Relatively inexpensive
Can be performed at any time of year (with appropriate reference ranges)

Limitations:

Sample handling is critical—blood must be collected in specialized tubes, kept cold, and processed quickly or ACTH degrades
Seasonal variation requires using appropriate reference ranges
May miss early or mild cases

TRH Stimulation Test

The thyrotropin-releasing hormone (TRH) stimulation test provides a more sensitive diagnostic method:

Procedure:

Baseline blood sample collected for ACTH measurement
TRH injected intravenously (1 mg for adult horses)
Second blood sample collected 10 minutes post-injection for ACTH measurement
Post-TRH ACTH concentration compared to diagnostic cutoff values

Interpretation: In horses with PPID, the dysfunctional pars intermedia shows exaggerated response to TRH stimulation, producing ACTH levels that exceed established cutoffs.

Advantages:

More sensitive than baseline ACTH—detects earlier/milder disease
Less affected by seasonal variation
Fewer false negatives

Limitations:

More expensive (requires TRH, which has become expensive and sometimes difficult to obtain)
Requires two blood samples and precise timing
Not all laboratories offer TRH stimulation testing
Some experts question whether detecting very mild/early disease that may not require treatment justifies the additional expense

Dexamethasone Suppression Test

The overnight dexamethasone suppression test, commonly used to diagnose Cushing’s syndrome in humans and dogs, is generally NOT recommended in horses due to significant risk of triggering laminitis in susceptible individuals. This test should be avoided in equine patients.

Insulin and Glucose Testing

While not diagnostic for PPID specifically, measuring insulin and glucose helps:

Identify concurrent insulin dysregulation (common in PPID horses)
Assess laminitis risk
Guide dietary management

Tests include:

Baseline insulin and glucose
Oral sugar test (measuring insulin response to oral carbohydrate challenge)
Combined glucose-insulin test

When to Test

Timing considerations:

Seasonality: Fall (late August through October) represents the highest-risk period for elevated ACTH. Testing during this period may increase diagnostic sensitivity but requires using season-specific reference ranges. Some experts recommend testing in fall for maximum sensitivity; others prefer testing at other times to avoid seasonal confounding.

Clinical suspicion: Horses showing clinical signs suggesting PPID should be tested regardless of season.

Screening older horses: Some veterinarians recommend screening all horses over 15 years even without obvious signs, as early detection enables earlier intervention.

Diagnostic Challenges

Early disease: Horses in early PPID stages may have normal or borderline test results despite having the condition. Serial testing (repeating tests 6-12 months later) may be necessary.

Seasonal athletes: Competition horses showing clinical signs during show season but tested at other times may have false negative results.

Clinical diagnosis: Horses with classic signs (advanced hirsutism, characteristic body condition changes, recurrent laminitis) may be diagnosed clinically and treated even with normal test results, as tests have imperfect sensitivity.

Treatment of PPID

While PPID cannot be cured, effective treatment dramatically improves clinical signs, prevents complications, and maintains quality of life. The primary treatment involves medication to address the underlying pituitary dysfunction, combined with comprehensive management addressing diet, environment, and concurrent problems.

Pergolide Mesylate (Prascend®)

Pergolide, a dopamine agonist medication, represents the gold standard treatment for PPID and the only FDA-approved medication for this condition in horses.

Mechanism of Action

Pergolide is a dopamine agonist, meaning it binds to and activates dopamine receptors. By mimicking dopamine’s action, pergolide compensates for the loss of natural dopaminergic inhibition of the pars intermedia. This suppresses the excessive hormone production by the dysfunctional pituitary, reducing ACTH and other hormone levels toward normal.

Administration

Dosing:

Standard starting dose: 2 mcg/kg (approximately 1 mg per 500 kg/1100 lb horse) once daily
Given orally, typically as tablets administered in feed or treats
Dose may need adjustment based on individual response—some horses require higher doses (up to 5-10 mg daily or more) for adequate control

Long-term treatment: Pergolide must be given daily for the remainder of the horse’s life. PPID is progressive and incurable; medication controls signs but doesn’t cure the underlying condition. Discontinuing treatment results in recurrence of clinical signs.

Monitoring Treatment Response

Clinical monitoring:

Improvement in hair shedding (may take 6-12 months for full effect on existing coat)
Restoration of normal body condition and muscle development
Increased energy and improved attitude
Resolution of PU/PD
Reduced infection frequency
Most importantly, prevention of laminitis

Laboratory monitoring:

Repeat ACTH testing 4-6 weeks after starting treatment, then periodically (every 6-12 months or if clinical signs recur)
Dose adjusted to achieve ACTH levels within reference ranges
Seasonal variation means fall testing typically shows higher values requiring temporary dose increases

Effectiveness

Studies demonstrate that 70-80% or more of horses show significant improvement with pergolide treatment. Clinical signs may improve within weeks to months, though full response to some changes (like coat normalization) takes longer.

Benefits include:

Normalized hair shedding and coat quality
Improved body condition and muscle development
Increased energy and improved quality of life
Dramatically reduced laminitis risk
Better immune function with fewer infections
Resolution of PU/PD

Side Effects

Pergolide is generally very well tolerated with few side effects. Occasionally, horses experience:

Mild gastrointestinal upset:

Temporary decreased appetite
Mild colic signs
Loose manure

These effects typically resolve within days and can be minimized by:

Starting at a low dose and gradually increasing
Giving medication with feed
Dividing the dose (giving half twice daily)

Lethargy or depression: Rarely, horses become dull or sleepy, usually indicating excessive dosing. Reducing the dose resolves this.

Other uncommon effects: Sweating, agitation, or behavioral changes occur rarely.

Most horses tolerate pergolide without any adverse effects and continue treatment for years without problems.

Cost Considerations

Pergolide represents a long-term financial commitment:

Brand name Prascend costs approximately $2-4 per day ($60-120 per month)
Compounded pergolide from specialized pharmacies costs less (approximately $30-60 per month)
Debate exists about whether compounded formulations are as effective and stable as brand name product
Cost increases for horses requiring higher doses

Despite the expense, most owners find the dramatic improvement in their horses’ quality of life and prevention of costly laminitis episodes justifies the treatment cost.

Alternative Medications

Cyproheptadine

This serotonin antagonist was used before pergolide became available:

Mechanism: Blocks serotonin, which may have some effect on pituitary function

Effectiveness: Significantly less effective than pergolide—studies show limited or inconsistent benefit

Current use: Rarely used as primary treatment; occasionally tried in horses that cannot tolerate pergolide or when pergolide is unavailable

Dosing: 0.3 mg/kg once or twice daily orally

Trilostane

This medication inhibits cortisol synthesis and is used in dogs with Cushing’s syndrome:

Use in horses: Not recommended—safety and efficacy in horses not established, and several cases of serious adverse effects have been reported

Management and Supportive Care

Medication alone is insufficient—comprehensive management addressing all aspects of the horse’s health optimizes outcomes.

Dietary Management

Low sugar/starch diet reduces insulin spikes and laminitis risk:

Forage-based diet with tested hay containing less than 10% NSC (non-structural carbohydrates = sugar + starch)
Soak hay if NSC content unknown or excessive—30-60 minutes in cold water reduces sugars
Avoid grain-based feeds—use low-NSC complete feeds or ration balancers if needed
Eliminate treats high in sugar (apples, carrots, commercial treats)—use low-sugar alternatives if treats desired
Restrict pasture access, particularly during high-risk periods (spring, fall, after frost, sunny afternoons)—use grazing muzzles if pasture access needed

Balanced nutrition: Ensure adequate protein, vitamins, and minerals while controlling calories:

Ration balancers provide essential nutrients in small volumes
Vitamin E supplementation may help older horses
Maintain appropriate body weight—neither too fat nor too thin

Exercise

Regular, appropriate exercise:

Maintains muscle mass and strength
Improves insulin sensitivity
Supports overall health and quality of life
Adjust intensity to horse’s capabilities—many PPID horses can continue riding or light work

Hoof Care

Meticulous farrier care:

Regular trimming (every 4-6 weeks)
Appropriate shoeing or trimming for any existing laminitic changes
Monitor closely for early laminitis signs

Body Clipping

Horses with severe hirsutism benefit from body clipping:

Improves comfort, particularly in warm weather
Allows better skin monitoring for infections
Improves appearance
May need repeated clipping throughout the year as hair regrows
Blanket if needed after clipping in cold weather

Dental Care

Regular dental examinations and floating (every 6-12 months):

PPID horses more prone to dental problems
Good dental health ensures adequate nutrition

Parasite Control

Appropriate deworming:

PPID horses may have compromised immunity affecting parasite resistance
Fecal egg counts guide deworming frequency
Maintain good pasture hygiene

Infection Prevention and Treatment

Prompt treatment of any infections
Good hygiene and grooming to prevent skin infections
Monitor wounds carefully and treat aggressively
Vaccinations kept current (though immune response may be reduced)

Environmental Management

Adequate shelter from weather extremes
Clean, dry living conditions reducing infection risk
Appropriate socialization with compatible companions
Stress reduction—minimize changes and disruptions

Prognosis and Quality of Life

With appropriate treatment and management, most horses with PPID can maintain good quality of life for years:

Early diagnosis and treatment provides the best outcomes:

Many horses live comfortably into their late twenties or thirties
Continue useful activities including light riding
Maintain good overall health

Poorly controlled or untreated PPID leads to:

Progressive deterioration
Recurrent infections
Severe laminitis often resulting in euthanasia
Decreased quality of life
Shortened lifespan

Key prognostic factors:

Timeliness of diagnosis—earlier is better
Consistent treatment compliance—daily pergolide without gaps
Quality of management—diet, environment, preventive care
Concurrent conditions—horses with severe laminitis, metabolic syndrome, or other problems face greater challenges
Owner commitment and resources

Realistic expectations: While treatment dramatically improves outcomes, PPID is progressive. Over years, clinical signs may gradually worsen despite treatment, requiring dose adjustments or additional management modifications. Eventually, age-related decline or complications may necessitate difficult end-of-life decisions.

Prevention

Unfortunately, PPID cannot be prevented, as the underlying cause (pituitary degeneration) appears to be an inevitable consequence of aging in susceptible individuals. No dietary, management, or medical interventions have been proven to prevent PPID development.

However, several strategies may help:

Regular screening of older horses enables early detection:

Annual ACTH testing of horses over 15 years
Testing horses with subtle signs that might indicate early disease
Early treatment may slow progression

Excellent general health care supports overall wellness:

Proper nutrition
Regular exercise
Dental care
Parasite control
Prompt treatment of health issues

Minimizing stress may theoretically help, as chronic stress affects the hypothalamic-pituitary axis, though no direct evidence proves this prevents PPID.

PPID vs. Equine Metabolic Syndrome

PPID and Equine Metabolic Syndrome (EMS) are distinct conditions that sometimes coexist and share some features, creating confusion:

PPID (Cushing’s Disease):

Primarily affects older horses (typically >15 years)
Caused by pituitary dysfunction
Characterized by elevated ACTH
Hirsutism is characteristic
Muscle wasting with pot-bellied appearance
PU/PD common
Increased infection susceptibility
Treated with pergolide

EMS:

Affects horses of any age, often middle-aged
Metabolic disorder involving insulin dysregulation
Normal ACTH (unless concurrent PPID)
Normal coat shedding
Obesity with abnormal fat distribution (cresty neck)
No PU/PD
Normal immune function
Treated with diet, exercise, weight loss

Overlap:

Both increase laminitis risk significantly
Both may involve insulin dysregulation
Can coexist in the same horse
Similar dietary management appropriate for both

Distinguishing the conditions requires appropriate diagnostic testing (ACTH for PPID; insulin testing for EMS) and clinical assessment.

Common Questions and Misconceptions

“Is Cushing’s disease the same in horses as in humans/dogs?”

The name is the same, but the specific disorder differs. Human and canine Cushing’s syndrome typically involves the anterior pituitary or adrenal glands producing excessive cortisol. Equine PPID involves the intermediate pituitary producing excessive ACTH and related peptides. While there are similarities, the underlying pathology, diagnostic tests, and treatments differ among species.

“Will my horse with PPID definitely get laminitis?”

Not necessarily, but risk is dramatically increased. With excellent management—particularly dietary control and pergolide treatment—many PPID horses never develop laminitis. However, vigilance is essential as even well-managed horses remain at higher risk than unaffected horses.

“Can PPID be cured?”

No. PPID is a progressive, incurable condition. However, it can be very effectively managed with daily medication and appropriate care, allowing affected horses to live comfortably for years.

“My horse has a long coat but tests negative for PPID. What does this mean?”

Several possibilities exist:

Very early disease with intermittent hormone elevations not captured by testing—retest in 6-12 months
False negative test result—consider TRH stimulation test for greater sensitivity
Other causes of delayed shedding (nutritional deficiencies, other endocrine disorders, individual variation)

Discuss with your veterinarian whether empirical treatment trial or additional testing is appropriate.

“Can I treat PPID with supplements instead of medication?”

No scientifically proven supplements effectively treat PPID. While numerous products are marketed claiming to support pituitary health or treat Cushing’s disease, none have demonstrated efficacy in controlled studies. Pergolide remains the only proven effective treatment. Some supplements may provide general health support but cannot replace pergolide for managing PPID.

Research and Future Directions

Ongoing research continues improving our understanding of PPID:

Investigation of the underlying mechanisms causing pituitary degeneration
Development of biomarkers for earlier diagnosis
Studies of genetic susceptibility factors
Evaluation of novel treatments
Long-term studies assessing optimal management strategies
Understanding the relationship between PPID and laminitis pathophysiology

Conclusion

Cushing’s disease in horses (Pituitary Pars Intermedia Dysfunction or PPID) represents a common and clinically significant endocrine disorder affecting older horses. This progressive condition results from dysfunction of the pituitary gland’s intermediate lobe, causing excessive production of ACTH and related hormones. The resulting hormonal imbalances create a characteristic syndrome including hirsutism (long, non-shedding coat), muscle wasting with pot-bellied appearance, increased drinking and urination, immune suppression with frequent infections, lethargy, and most seriously, dramatically increased laminitis risk.

Diagnosis requires combining clinical findings with laboratory testing, primarily measurement of ACTH levels in blood plasma. The TRH stimulation test provides enhanced diagnostic sensitivity for detecting early or mild disease.

Treatment with pergolide mesylate (Prascend®) represents the gold standard approach, effectively controlling clinical signs in 70-80% or more of horses. This dopamine agonist medication compensates for the loss of natural dopaminergic inhibition of the pituitary, reducing excessive hormone production. Daily pergolide treatment, continued for the remainder of the horse’s life, combined with comprehensive management including dietary control (low sugar/starch diet), regular exercise, meticulous hoof care, and prompt treatment of infections, enables most affected horses to maintain good quality of life for years.

Early diagnosis and prompt treatment initiation provide the best outcomes, preventing serious complications—particularly laminitis—and maintaining horses’ health, comfort, and usefulness. While PPID is progressive and incurable, appropriate management dramatically improves both quality and potentially length of life for affected horses.

Understanding PPID—its signs, diagnosis, and treatment—represents essential knowledge for anyone caring for older horses. Regular screening of horses over 15 years, prompt investigation of suggestive clinical signs, and committed implementation of treatment protocols when PPID is diagnosed optimize outcomes and allow these older horses to continue enjoying comfortable, active lives despite their endocrine disorder.