Study sharpens thyroid testing guidance for healthy donkeys
Bottom line
Assessment of thyroid hormones in healthy donkeys got a species-specific update this week, with researchers reporting the first donkey data generated on the Siemens Immulite 2000xpi chemiluminescent immunoassay platform that’s commonly used in equine endocrine testing. In the July 15, 2026 issue of Veterinary Sciences, investigators measured free and total T4 and T3 in 40 healthy donkeys and 41 horses and found that donkeys had higher serum thyroid hormone concentrations than horses on this analyzer, while age and sex did not significantly affect results in the donkey cohort. The study also found the canine TSH kit performed poorly, with high imprecision, and concluded it isn’t valid for measuring TSH in equids. (mdpi.com)
Why it matters: For veterinarians, the practical message is that horse-based interpretation can still mislead when testing donkeys. Earlier work had already shown that healthy donkeys run higher thyroid hormone concentrations than horses, raising the risk of misdiagnosing thyroid dysfunction if clinicians apply equine expectations too broadly. This new paper matters because it updates that point using the Immulite 2000xpi platform now referenced in broader equine endocrine guidance, and it suggests T4-based measurements on this analyzer were more analytically reliable than T3-based measurements in this dataset. More broadly, equine thyroid testing remains tricky even in horses because thyroid values are influenced by age, illness, nutrition, drugs, and other nonthyroidal factors, so donkey-specific reference thinking is important before labeling an animal hypothyroid. (mdpi.com)
What to watch: The next step is whether larger studies establish analyzer-specific reference intervals for donkeys, and whether diagnostic labs and endocrine guidance begin spelling out donkey-specific interpretation rather than relying on horse data. (mdpi.com)
Key facts
- Study type
- Thyroid hormone assessment in healthy donkeys and horses
- Publication date
- July 15, 2026
- Journal
- Veterinary Sciences
- Analyzer
- Siemens Immulite 2000xpi chemiluminescent immunoassay
- Sample size
- 40 healthy donkeys, 41 horses
- Main finding
- Healthy donkeys had higher serum thyroid hormone concentrations than horses on this platform
- TSH result
- Canine TSH kit had high imprecision and was not valid for equids
- Donkey cohort finding
- Age and sex did not significantly affect results
- Assay note
- T4 assays were more analytically reliable than T3 assays in this dataset
A new donkey endocrinology study is putting a finer point on an old clinical problem: donkeys aren’t just small horses when it comes to thyroid testing. In a paper published July 15, 2026 in Veterinary Sciences, researchers reported the first thyroid hormone data from healthy donkeys generated with the Immulite 2000xpi, a chemiluminescent immunoassay analyzer widely used in equine endocrine work. Their headline finding was straightforward: healthy donkeys had higher thyroid hormone concentrations than horses on this platform, and the canine TSH kit showed too much imprecision to be considered valid for equids. (mdpi.com)
That finding builds on a smaller but important body of earlier literature. A 2013 study in Equine Veterinary Journal found that healthy adult donkeys had higher thyroid hormone concentrations than healthy horses and warned that species-specific reference intervals were needed to avoid misdiagnosis. More recent donkey endocrine reviews have repeated that caution, noting that donkeys differ from horses across several endocrine measures and that borrowing horse cutoffs can create diagnostic error. (pubmed.ncbi.nlm.nih.gov)
In the new study, the authors measured serum free and total T4 and T3 in 40 healthy donkeys, average age 6.1 years, and 41 horses, average age 10.7 years, using the Immulite 2000xpi. According to the journal abstract, T4 assays on the platform showed lower intra-assay variability and fewer below-detection-limit results than T3 assays. The donkey cohort did not show significant differences by age or sex, which contrasts somewhat with earlier radioimmunoassay-based work that suggested younger donkeys may have higher values for some thyroid markers. That difference may reflect assay platform effects, sample size, population differences, or all three. (mdpi.com)
The TSH result may be the most immediately actionable laboratory detail. The authors reported that the canine TSH kit had high imprecision and concluded it isn’t valid for equine use. That fits a broader pattern in endocrine testing: assay choice matters, and cutoffs often can’t be transferred cleanly across platforms or species. Equine endocrine guidance already distinguishes analyzer-specific thresholds for tests such as insulin and ACTH, particularly for the Immulite 2000xpi, because assay bias can materially change interpretation. (mdpi.com)
Outside commentary specific to this paper was limited at the time of writing, but the surrounding expert literature is consistent on the core message. Cornell’s equine thyroid testing guidance emphasizes that specimen type and handling can affect results, and a 2024 review on thyroid disorders in horses notes that blood thyroid hormone concentrations are influenced by many nonthyroidal factors, making over-interpretation risky even in the species for which most assays are used. In other words, if thyroid testing is nuanced in horses, it’s even more important not to overextend horse-based assumptions to donkeys. (vet.cornell.edu)
Why it matters: For veterinary professionals, this study is less about proving that donkey thyroid physiology is different, and more about aligning that knowledge with the analyzer many labs and clinicians actually use. If a donkey’s thyroid panel is read through a horse lens, clinicians risk chasing disease that isn’t there, or misclassifying normal donkey physiology as abnormal. The paper also suggests that some analytes on the platform may be more dependable than others, which could shape how clinicians prioritize total versus free hormone measurements, and how much weight they place on T3 versus T4 results in routine workups. (mdpi.com)
There’s also a workflow implication for mixed equine practices and referral labs. Donkeys are overrepresented in endocrine discussions around obesity, hyperlipemia, and pituitary pars intermedia dysfunction, and endocrine reviews increasingly stress that donkey-specific interpretation is needed across these conditions. A paper like this gives clinicians and labs a better basis for reporting donkey thyroid results with appropriate cautionary notes, rather than defaulting to horse reference expectations. (pmc.ncbi.nlm.nih.gov)
What to watch: The next milestones are larger validation studies, formal reference interval work on the Immulite 2000xpi and other platforms, and whether veterinary diagnostic labs or endocrine groups begin publishing donkey-specific interpretive guidance for thyroid testing. Until then, the safest takeaway is practical: use donkey context, not horse shortcuts, when interpreting thyroid hormone results. (mdpi.com)