Horse PPID Management: Seasonal ACTH Testing

Accurate diagnosis of PPID in horses requires awareness of seasonal ACTH fluctuations. Autumn testing requires different reference ranges to avoid over-diagnosis.

Key Facts

ACTH concentrations in horses naturally peak in August to October each year
Using non-seasonal reference ranges in autumn leads to false positive PPID diagnoses
The Equine Endocrinology Group publishes seasonally adjusted reference ranges annually
Horses on pergolide may need dose adjustment during the seasonal ACTH peak
Combining ACTH with TRH stimulation testing improves diagnostic sensitivity in early disease

Welfare Considerations

Misdiagnosis of PPID based on autumn ACTH without seasonal adjustment can lead to unnecessary lifelong medication. Conversely, failing to identify true PPID cases means horses experience preventable suffering from laminitis and metabolic dysfunction. Veterinary awareness of seasonal ACTH physiology has improved significantly in recent years. Horse owners who understand the seasonal testing schedule and push for appropriate interpretation of results play an active role in their horse welfare. Regular reassessment of drug dose is necessary as PPID is progressive.

What You Can Do

Test ACTH levels in autumn using the Equine Endocrinology Group seasonal reference ranges
Ensure your vet uses seasonally adjusted thresholds before starting or changing pergolide dose
Increase monitoring frequency if your horse is on pergolide going into autumn
Discuss TRH stimulation testing with your vet if early PPID is suspected but ACTH is borderline
Keep a medication and testing logbook to track disease progression over years