ACTH in Horses: Understanding, Testing, and Managing High Levels

If your horse has been diagnosed with elevated ACTH levels or you're concerned about Equine Cushing's Disease, understanding what ACTH means and how to manage it is crucial for your horse's health and quality of life. This comprehensive guide covers everything horse owners need to know about ACTH testing, normal ranges, and treatment options.

What is ACTH in Horses?

ACTH (Adrenocorticotropic Hormone) is a hormone produced by the pituitary gland that stimulates the adrenal glands to release cortisol. In healthy horses, ACTH levels remain within a normal range and follow seasonal patterns. However, when the pituitary gland becomes dysfunctional—a condition known as Pituitary Pars Intermedia Dysfunction (PPID) or Equine Cushing's Disease—ACTH production increases significantly.

Why ACTH Testing Matters

ACTH testing is the gold standard diagnostic tool for detecting PPID in horses. Early detection allows for prompt treatment, which can:

Prevent or minimize laminitis episodes

Improve coat quality and shedding patterns

Restore normal energy levels

Enhance immune function

Extend your horse's quality of life

Normal ACTH Levels in Horses

ACTH levels vary by season, making timing of testing critical:

Seasonal Reference Ranges:

November to July: Less than 35 pg/mL

August: Less than 47 pg/mL

September: Less than 100 pg/mL (peak season)

October: Less than 70 pg/mL

September shows the highest natural ACTH levels due to seasonal rise, which is why testing during this month requires different interpretation. Your veterinarian will account for seasonal variations when evaluating results.

Common Signs Your Horse May Have Elevated ACTH

Watch for these clinical signs that often accompany high ACTH levels:

Classic Symptoms

Hirsutism: Long, curly coat that fails to shed properly (most recognizable sign)

Laminitis: Recurrent or chronic founder episodes

Muscle wasting: Particularly along the topline

Pot-bellied appearance: Redistribution of fat deposits

Lethargy: Decreased performance and energy

Increased drinking and urination: Polydipsia and polyuria

Abnormal fat deposits: Especially above the eyes and tail head

Poor wound healing: Compromised immune function

Increased sweating: Or paradoxically, decreased sweating

Not all horses display every symptom, and early cases may show subtle signs. Senior horses (15+ years) are most commonly affected, though PPID can occur in younger animals.

ACTH Testing: What to Expect

When to Test

Late summer/early fall (August-October) for highest diagnostic sensitivity

Any time of year if clinical signs are present

Annually for senior horses as preventive screening

Before starting or adjusting pergolide treatment

Testing Process

Your veterinarian will draw a blood sample, ideally in the morning. The sample must be handled carefully and shipped on ice to maintain accuracy. Results typically return within 3-7 days.

Interpreting Results

Normal: ACTH within seasonal reference range

Equivocal: Borderline results may warrant repeat testing or TRH stimulation test

Elevated: Confirms PPID diagnosis;

treatment recommended

Treatment Options for High ACTH

Pergolide: The Primary Treatment

Pergolide mesylate is the only FDA-approved medication for treating PPID in horses. It works by mimicking dopamine, which inhibits ACTH production from the pituitary gland.

Starting Dose: Typically 0.002 mg/kg (approximately 1 mg for a 500 kg horse) once daily

Monitoring: ACTH levels should be rechecked 4-6 weeks after starting treatment or dose adjustments, then every 6-12 months

Adjustments: Dosage may need seasonal adjustments, with higher doses often required in fall

Response Time: Most horses show clinical improvement within 6-12 weeks

Medication Tips

Give pergolide with food to improve palatability

Consistent daily administration is crucial

Never abruptly discontinue medication

Store in a cool, dry place away from light

Generic and compounded versions are available at lower cost than brand-name Prascend

Management Strategies Beyond Medication

Dietary Considerations

Low sugar/starch diet:

Reduce risk of laminitis

High-quality forage: Foundation of the diet

Avoid lush pasture: Especially during high-sugar times (morning, spring)

Use grazing muzzles: If pasture access is necessary

Balance minerals: Ensure adequate vitamin E, magnesium, and trace minerals

Hoof Care

Regular farrier visits (every 4-6 weeks)

Radiographs if laminitis suspected

Supportive shoeing or trimming as needed

Monitor digital pulses and hoof temperature

Exercise and Environment

Maintain regular, appropriate exercise

Provide shade and fans during hot weather

Body clip if excessive coat persists

Reduce stress where possible

Dental Care

Regular dental examinations become even more important as PPID can affect overall health and immune function.

Long-Term Prognosis

With appropriate treatment and management, most horses with PPID can maintain good quality of life for years. The key factors for success include:

Early diagnosis and treatment initiation

Consistent medication compliance

Regular ACTH monitoring

Appropriate diet and management

Close veterinary partnership

When to Retest ACTH Levels

4-6 weeks after starting pergolide

4-6 weeks after any dose adjustment

Every 6-12 months once stabilized

If clinical signs worsen or new symptoms appear

Seasonally (especially in fall) to assess if dose adjustments needed

Cost Considerations

ACTH test: $75-150 per test

Pergolide: $30-80+ per month depending on dose and source

Follow-up care: Variable based on individual needs

Many horse owners find that generic pergolide or compounded versions significantly reduce medication costs while maintaining effectiveness.

Frequently Asked Questions

Can PPID be prevented?

Currently, there's no known prevention.

Regular screening of senior horses allows for early detection.

Will my horse always need medication?

PPID is a progressive condition. Once started, pergolide is typically continued for life.

Can diet alone control ACTH levels?

While diet is important for managing symptoms (especially laminitis risk), medication is necessary to address the underlying hormonal dysfunction.

Is PPID the same as Equine Metabolic Syndrome (EMS)?

No, though they can occur together. EMS involves insulin dysregulation, while PPID is pituitary dysfunction. Both increase laminitis risk.

Take Action

If you suspect your horse may have elevated ACTH levels or PPID, schedule an appointment with your veterinarian for testing. Early diagnosis and treatment dramatically improve outcomes and quality of life. With proper management, many horses with PPID continue to thrive as valued companions and even competitive athletes.

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