Influence of feeding and other factors on adrenocorticotropin concentration and thyrotropin-releasing hormone stimulation test in horses and ponies.
Authors: Drozdzewska Karolina, Winter Judith, Barton Ann Kristin, Merle Roswitha, Gehlen Heidrun
Journal: Equine veterinary journal
Summary
# Editorial Summary Pituitary pars intermedia dysfunction (PPID) diagnosis relies on measuring baseline adrenocorticotropin (ACTH) and post-thyrotropin-releasing hormone (TRH) stimulated ACTH concentrations, yet significant variation in these values across populations and seasons complicates interpretation of results and risks both false positives and false negatives in clinical practice. Drozdzewska and colleagues conducted a comprehensive investigation into how feeding practices, alongside age, breed, colour, sex and season, influence both basal and stimulated ACTH values in horses and ponies, addressing conflicting evidence in the literature about nutritional effects on these diagnostic markers. The researchers found substantial seasonal fluctuations in ACTH concentrations—particularly during autumn—and documented previously underexplored interactions between feeding type and diagnostic outcomes, with certain feed compositions producing measurable effects on both basal and stimulated hormone levels. These findings have direct implications for practitioners interpreting PPID diagnostic results: feeding protocols should be standardised prior to testing where possible, baseline reference ranges may require adjustment according to season and individual factors (breed, age, colour), and clinicians should exercise caution when comparing results across different nutritional management scenarios. Understanding these contextual variables will improve diagnostic accuracy and reduce unnecessary treatment initiation or misdiagnosis of PPID in horses presenting with ambiguous clinical signs.
Read the full abstract on PubMed
Practical Takeaways
- •When interpreting ACTH results for PPID diagnosis, account for seasonal effects, age, breed, and colour as these significantly influence baseline values and test interpretation
- •Clarify feeding protocols with your diagnostic laboratory before ACTH testing, as feeding effects on results remain poorly standardized and may affect result reliability
- •Use TRH stimulation testing alongside basal ACTH rather than relying on either test alone for more accurate PPID diagnosis
Key Findings
- •Multiple factors influence basal ACTH concentration including disease, age, and seasonal variation (with autumn-specific effects for breed, colour, and sex)
- •TRH stimulation test (pACTH) is recommended for PPID diagnosis alongside basal ACTH measurements
- •Conflicting evidence exists regarding the impact of feeding on basal and post-stimulation ACTH concentrations
- •Standardization of testing conditions is needed to improve diagnostic accuracy for PPID in horses and ponies