PSIII-29 Anti-inflammatory ω-3 polyunsaturated fatty acid supplements improved insulin-to-glucose ratios in high adiposity heat-stressed finishing lambs.

Abstract Heat stress disrupts metabolic homeostasis in livestock in part by impairing glucose regulation. Heat stress-induced systemic inflammation is a mediating factor in poor metabolism, and adiposity-induced inflammation may further disrupt energy balance. This study sought to evaluate the effects of heat stress, high adiposity, and dietary supplementation of an anti-inflammatory nutraceutical on insulin-glucose homeostasis in commercial Rambouillet-cross wether lambs. Wethers were categorized as low (< 5 mm) or high (≥ 5 mm) adiposity based on ultrasound-estimated backfat thickness. Wethers in each category were randomly assigned to be maintained under heat stress conditions (40 °C, 35% humidity) or pair-fed under thermoneutral conditions (20 °C, 15% humidity) for 21 d. High-adiposity heat-stressed wethers were randomly assigned to receive daily oral ω-3 polyunsaturated fatty acid (ω-3 PUFA) Ca²⁺ salt (0.42 g/kg) supplementation or a placebo. This created five experimental groups of wethers: lean controls (n = 8), high-adiposity controls (n = 8), lean heat-stressed (n = 8), high-adiposity heat-stressed (n = 8), and high-adiposity heat-stressed + ω-3 PUFA (n = 7). A glucose tolerance test was performed on d 14 to assess glucose clearance and insulin response. Blood samples were collected by jugular venipuncture at -10, 5, 10, 30, 60, and 120 min following a glucose bolus, and circulating glucose, insulin, and lactate concentrations were determined. Heat-stressed did not affect plasma insulin or blood lactate at any time point but reduced (P = 0.03) blood glucose concentrations by an average of 10%. The greatest effects of heat stress on glucose were observed within the first 30 min of the bolus. High adiposity had minimal effect on glucose, insulin, or lactate. Dietary supplementation of ω-3 PUFA increased (P = 0.02) glucose concentrations by an average of 23%. This in turn reduced (P = 0.04) insulin-to-glucose ratios by 24%, which would indicate improved insulin sensitivity for glucose clearance. These findings indicate that heat stress and high adiposity have consequences for insulin-glucose homeostasis in sheep, which help explain previously-observed metabolic inefficiency. Conversely, dietary supplementation with anti-inflammatory ω-3 PUFA may have the potential to mitigate metabolic disruptions by improving insulin sensitivity.