Characterization of the intravenous glucose tolerance test and the combined glucose-insulin test in donkeys.
Authors: Mendoza F J, Aguilera-Aguilera R, Gonzalez-De Cara C A, Toribio R E, Estepa J C, Perez-Ecija A
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Glucose Tolerance Testing in Donkeys Understanding how donkeys metabolise glucose is essential for identifying endocrine disorders, yet standardised testing protocols have been unavailable for this species. Mendoza and colleagues conducted intravenous glucose tolerance tests (IVGTT) and combined glucose-insulin tests (CGIT) on 16 healthy adult donkeys, establishing reference ranges for glucose and insulin dynamics that clinicians can use to identify metabolic dysfunction. During the IVGTT, blood glucose peaked at 323 mg/dL and cleared at 1.28 mg/dL/minute, whilst the CGIT—which more closely mimics insulin secretion—demonstrated faster initial glucose clearance (2.01 mg/dL/minute) but a prolonged negative phase lasting 256 minutes. Critically, these glucose-insulin responses differed meaningfully from those documented in horses, indicating that donkey-specific reference intervals are necessary to avoid misdiagnosis of conditions such as equine metabolic syndrome or pituitary pars intermedia dysfunction. Practitioners evaluating donkey metabolism should now utilise these species-specific thresholds rather than extrapolating from equine data, improving diagnostic accuracy for animals presenting with obesity, insulin resistance, or suspected endocrine disease.
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Practical Takeaways
- •Donkeys have different glucose-insulin responses than horses, so clinicians must use donkey-specific reference values rather than applying equine standards when assessing metabolic dysfunction
- •The IVGTT and CGIT are now characterized and validated in donkeys, providing practitioners with reference parameters for diagnosing insulin dysregulation and metabolic disease in this species
- •Species-specific testing protocols are essential for accurate endocrine evaluation in donkeys and should not be extrapolated from equine medicine
Key Findings
- •IVGTT in donkeys showed positive phase lasting 160.9±13.3 min with peak glucose of 323.1±9.2 mg/dL and decline rate of 1.28±0.15 mg/dL/min
- •CGIT positive phase lasted 44±3 min with glucose clearance rate of 2.01±0.18 mg/dL/min, followed by negative phase lasting 255.9±3 min
- •Glucose and insulin AUC values established for healthy adult donkeys: IVGTT glucose AUC 21.4±1.9×10³ mg/dL/min, insulin AUC 7.2±0.9×10³ µIU/mL/min
- •Distinct glucose dynamics in donkeys compared to horses support use of species-specific protocols for endocrine assessment