Thyroid hormone concentrations differ between donkeys and horses.
Authors: Mendoza F J, Perez-Ecija R A, Toribio R E, Estepa J C
Journal: Equine veterinary journal
Summary
# Editorial Summary Thyroid hormone reference intervals have never been formally established for donkeys, creating a diagnostic minefield where equine reference ranges are inappropriately applied—potentially leading to over- or under-diagnosis of thyroid disease in this species. Mendoza and colleagues measured five thyroid parameters (free and total T3, free and total T4, and reverse T3) via radioimmunoassay in 38 healthy Andalusian donkeys across three age groups and 19 healthy horses, with all sampling standardised to morning collections and stringent health criteria. Donkeys consistently exhibited significantly higher thyroid hormone concentrations than horses across all measured parameters (P<0.01), with age-related trends emerging in donkeys alone: younger animals (<5 years) showed elevated reverse T3, free T4 and total T4 compared to older cohorts, whilst donkeys over 11 years demonstrated suppressed free and total T3 concentrations relative to younger groups. Gender had no discernible influence on thyroid hormone levels in either species. For practitioners, these findings underscore the critical need for species-specific—and potentially age-stratified—reference ranges when interpreting thyroid panels in donkeys, as using equine thresholds risks misclassifying normal donkey physiology as pathological and obscuring genuine endocrine dysfunction.
Read the full abstract on PubMed
Practical Takeaways
- •Do not use horse thyroid hormone reference ranges for donkeys, as values differ significantly and may lead to misdiagnosis of thyroid dysfunction
- •Establish and use species-specific reference intervals when interpreting thyroid function tests in donkeys versus horses
- •Age-related differences exist in donkeys, with younger animals showing higher hormone concentrations, particularly for reverse T3 and T4 forms
Key Findings
- •Serum thyroid hormone concentrations were significantly higher in donkeys than horses (P<0.01)
- •Donkeys <5 years had higher rT3, fT4, and tT4 than older donkeys (P<0.05)
- •Older donkeys (>11 years) had lower fT3 and tT3 than younger groups (P<0.05)
- •No gender differences in thyroid hormone concentrations were found across all measured parameters