Seasonal variation of endogenous adrenocorticotropic hormone concentrations in healthy non-geriatric donkeys in Northern California.
Authors: Humphreys Sarah, Kass Philip H, Magdesian K Gary, Goodrich Erin, Berryhill Emily
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Interpreting endocrine dysfunction in donkeys currently relies on equine reference ranges for adrenocorticotropic hormone (ACTH), yet donkeys naturally maintain higher baseline concentrations than horses and exhibit pronounced seasonal fluctuation that differs meaningfully from equine patterns. This 12-month prospective study tracked monthly plasma ACTH concentrations in 26 clinically healthy donkeys (median age 6 years; 10 standard and 16 miniature breeds) housed at a single Northern California facility, establishing clear circannual variation with winter and spring nadirs of 12.8 and 12.5 pg/ml respectively, summer elevation to 53.2 pg/ml, and autumn peaks reaching 77.1 pg/ml, with September concentrations maxing at 122.0 pg/ml. Critically, donkey ACTH values exceeded published equine reference ranges from May through November, with the most dramatic increases occurring during late summer and autumn months—a pattern paralleling horses yet with substantially higher absolute values across all seasons. For practitioners screening donkeys for pituitary pars intermedia dysfunction (PPID), these findings underscore that equine thresholds are inappropriate for accurate diagnosis; adopting species-specific reference intervals is essential to avoid misclassification of healthy animals as endocrinopathic and conversely to prevent missing genuine cases of PPID in affected individuals.
Read the full abstract on PubMed
Practical Takeaways
- •When screening donkeys for PPID, use donkey-specific ACTH reference ranges rather than equine ranges, as healthy donkeys have naturally higher baseline ACTH concentrations year-round
- •ACTH testing in donkeys should ideally be performed in winter or spring months when concentrations are lowest and most stable, improving diagnostic accuracy
- •Fall ACTH elevations in donkeys follow the same seasonal pattern as horses but reach higher absolute values—be aware of this seasonal variation to avoid misdiagnosis
Key Findings
- •Donkey ACTH concentrations peak in fall (77.1 pg/ml) with highest levels in September (122.0 pg/ml), similar circannual pattern to horses but with higher absolute values
- •ACTH concentrations were lowest in winter and spring (12.8 and 12.5 pg/ml respectively) and elevated May through November compared to equine reference ranges
- •Donkey ACTH concentrations were consistently higher than horse reference ranges across all seasons, necessitating species-specific diagnostic thresholds