Effect of age and dietary carbohydrate profiles on glucose and insulin dynamics in horses

Abstract

Background: Glucose and insulin dynamics may be different in adult and aged horses. Objectives: To determine the effects of age and dietary carbohydrates on glucose and insulin dynamics in healthy horses. Study design: Balanced Latin square with four isocaloric diets: CONTROL (hay plus restricted-starch-and-sugar fortified pellets), STARCH (control plus kibbled corn), FIBER (control plus unmolassed sugar beet pulp/soybean hull pellets) and SUGAR (control plus dextrose powder). Methods: A total of 16 healthy Thoroughbreds and Standardbreds divided into two age groups: ADULT (8.8 ± 2.9 years; n = 8) and AGED (20.6 ± 2.1 years; n = 8). Following dietary adaptation, horses underwent an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT), modified oral sugar test (OST) and dietary meal challenge. Outcome variables included: insulin sensitivity (SI), disposition index (DI), glucose effectiveness (Sg) and acute insulin response to glucose (AIRg) from the FSIGTT; peak glucose, peak insulin, time to peak, area under the curve for glucose (AUCg) and insulin (AUCi) from the OST and dietary meal challenge. Data were analyzed using multivariable linear mixed regression modelling. Results: AIRg was higher in AGED (mean [95% confidence interval]; 582.0 [455.0–709.0]) vs. ADULT (358.0 [224.0–491.0]; P = 0.03). ADULT and AGED horses had a higher SI on STARCH (adult: 3.3 [2.3–4.2]; aged: 2.8 [1.9–3.7]) and SUGAR (adult: 3.4 [2.5–4.3]; aged: 4.0 [3.1–4.9]) diets compared with CONTROL (adult: 2.0 [1.1–2.9], P = 0.029 (starch), P = 0.009 (sugar); aged: 1.4 [0.5–2.2], P = 0.009 (starch), P < 0.001 (sugar)). Feeding a STARCH (adult: 21581.0 [15029.0–28133.0]; aged: 35205.0 [29194.0–41216.0]) or SUGAR (adult: 26050.0 [19885.0–32215.0]; aged: 25720.0 [19770.0–31670.0]) meal resulted in postprandial hyperinsulinaemia (AUCi). Main limitations: Study cohort contained two insulin-sensitive breeds and no insulin-resistant breeds. Conclusions: Age and diet should be considered when evaluating glucose and insulin dynamics.