Seasonal Insulin Responses to the Oral Sugar Test in Healthy and Insulin Dysregulated Horses.
Authors: Macon Erica Lyn, Harris Patricia, Barker Virginia Day, Adams Amanda A
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Insulin dysregulation (ID) in horses presents a significant laminitis risk, yet clinicians have lacked clarity on how seasonal variation affects the oral sugar test (OST)—the primary monitoring tool for this metabolic condition. Over two years, researchers administered the OST to 11 ID and 11 healthy control horses across all seasons, measuring both resting (basal) insulin and the 60-minute post-syrup insulin response, alongside body condition scoring, cresty neck assessments, and forage analysis. Insulin-dysregulated horses demonstrated consistently elevated insulin at both time points compared to controls, but their response pattern shifted seasonally: basal and stimulated insulin peaked in spring (being significantly higher than in summer and autumn), with winter 60-minute values also elevated relative to autumn. Notably, basal insulin alone confirmed ID status only 56% of the time across seasons, whereas the 60-minute post-sugar response was diagnostic in 94% of cases. For practitioners using OST to guide management decisions and laminitis prevention strategies, these findings underscore that the full two-timepoint OST protocol provides far more reliable and consistent diagnosis than basal measurement alone, regardless of seasonal metabolic fluctuations.
Read the full abstract on PubMed
Practical Takeaways
- •Use the 60-minute oral sugar test (T60) rather than resting insulin alone for more consistent diagnosis of insulin dysregulation across seasons—94% vs 56% accuracy
- •Expect ID horses to show higher insulin concentrations in spring; seasonal variation exists but should not prevent diagnosis if using the full OST protocol
- •Monitor body condition and cresty neck scoring in spring through fall as these measurements correlate with insulin dysregulation status and laminitis risk
Key Findings
- •ID horses had consistently higher basal (T0) and 60-minute (T60) insulin concentrations compared to non-ID horses across all seasons (P < 0.02)
- •ID horses showed seasonal variation in insulin responses with higher T0 and T60 values in spring compared to fall and summer (P < 0.01 and P < 0.05 respectively)
- •The 60-minute OST response (T60) confirmed insulin dysregulation status 94% of the time versus only 56% for basal insulin (T0)
- •Body condition score and cresty neck scores were significantly higher in ID versus non-ID horses in spring, summer, and fall (P < 0.02), while season did not affect bodyweight