The Seasonality of Serum Insulin Concentrations in Equids and the Association With Breed, Age, and Sex.
Authors: Lopes Ana, Huber Laura, Durham Andy E
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Reference ranges for equine serum insulin have long been static, yet this large-scale analysis of over 21,000 laboratory records reveals that basal insulin concentrations fluctuate significantly across seasons, with winter readings substantially elevated compared to spring, summer, and autumn—a pattern replicated in insulin response following oral sugar challenge (Karo syrup). Beyond seasonality, pronounced breed predispositions emerged, with Welsh ponies and Shetland ponies demonstrating markedly higher insulin concentrations than other breeds, whilst females consistently showed higher basal insulin than males, and advancing age associated with progressive increases in insulin levels. These findings have immediate relevance for practitioners interpreting insulin dysregulation diagnoses: winter baseline readings, breed genetics, age, and sex substantially influence values, meaning that current one-size-fits-all reference intervals may misclassify otherwise healthy animals or conversely mask genuine metabolic disease when these contextual factors are not considered. For farriers, vets and nutritionists managing equine metabolic syndrome and insulin resistance, incorporating seasonal timing, breed-specific expectations, and demographic variables into clinical interpretation should refine diagnostic accuracy and reduce unnecessary dietary or management interventions in genetically predisposed but metabolically normal individuals.
Read the full abstract on PubMed
Practical Takeaways
- •Laboratory reference ranges for insulin should account for seasonal variation, with winter baseline values expected to be higher; adjust clinical interpretation accordingly
- •Breed-specific insulin profiles matter clinically—Shetland and Welsh ponies are inherently higher insulin responders and require lower thresholds for metabolic disease concern
- •Sex and age influence insulin levels; older females will naturally have higher concentrations, which should inform your laminitis risk assessment and management strategy rather than trigger unnecessary treatment escalation
Key Findings
- •Basal serum insulin concentrations were significantly higher in winter compared to other seasons (p<0.001)
- •Serum insulin concentration post-Karo syrup administration was significantly higher in winter versus summer and fall (p<0.001)
- •Shetland ponies and Welsh ponies demonstrated significantly higher insulin concentrations than most other breeds (p<0.01 to p<0.001)
- •Females had significantly higher basal insulin than males (p<0.001), and insulin concentrations increased positively with age (p<0.001)