Factors associated with insulin responses to oral sugars in a mixed-breed cohort of ponies

Abstract

Background: Serum insulin concentration at 60 min (InsulinT60) during an oral sugar test (OST) indicates future laminitis risk and insulin dysregulation (ID). Associations between InsulinT60 and physical and owner-reported variables may help clinicians select individuals for ID testing. Associations between InsulinT60 and other metabolic markers may help elucidate ID pathophysiology. Objectives: To describe associations between (A) season, physically-apparent and owner-reported factors and binary InsulinT60 interpretation (initial models) and (B) variables included in the initial models, other metabolic markers and continuous InsulinT60 (full models). Study design: Prospective longitudinal. Methods: Non-laminitic ponies were examined and OSTs (0.3 mL/kg Karo syrup) performed every 6 months (autumn and spring) for ≤4 years. Factors associated with InsulinT60 were determined using mixed-effects models with physical, owner-reported, season and serum/plasma markers as fixed effects and pony and premises identifiers as random effects. Autumn and spring data were analysed separately for full models. Results: One thousand seven hundred and sixty-three OSTs from 367 ponies were included. High-risk InsulinT60 (>153 μIU/mL) was independently associated with (odds ratio, 95% confidence interval [CI]): age (1.36, 1.16–1.60), body condition score (BCS) (2.38, 1.21–4.69), and bulging supraorbital fatpads (7.25, 2.1–24.98). However, the initial models provided little explanatory power (Nakagawa R2 = 0.1–0.27). LoginsulinT60 was independently associated with (effect estimate, 95% CI): age (0.02, 0.01–0.04), Welsh/Welsh X breed (0.22, 0.05, 0.39), sex (gelding = −0.2, −0.34 to 0.06), BCS (0.16, 0.08–0.23), plasma adiponectin (−0.02, −0.02 to 0.01) and basal insulin (0.01, 0.01–0.01) in spring, and: age (0.03, 0.02–0.04), BCS (0.17, 0.08–0.26), bulging supraorbital fatpads (0.37, 0.2–0.54), turnout score (0.05, 0.02–0.09), plasma adiponectin (−0.01, −0.02 to 0.01), ACTH (per 10 pg/mL) (0.01, 0.00–0.01), triglycerides (0.28, 0.07–0.49) and InsulinT0 (0.01, 0.01–0.01) in autumn. Main limitations: Only non-laminitic ponies in one region were included. Conclusions: Owner-reported and physically-apparent data were limited InsulinT60 predictors. InsulinT60 is a complex trait, independently associated with numerous variables, some with seasonal interactions.