With increases in the frequency, intensity and duration of heat waves forecast plus increased participation in tropical agriculture, heat stress (HS) is both a current and emerging problem. To control body temperature during HS, pigs reduce metabolic heat production by lowering feed intake and increase energy expenditure to dissipate heat, resulting in a net loss in production efficiency. Insulin sensitivity improves peripheral blood flow and therefore radiant heat loss. Therefore the aim of this experiment was to investigate the benefits of cinnamon (Cinnamonium Zeylancium) on insulin sensitivity in heat stressed pigs. Thirty-six female Large White×Landrace (ca. 41.4 kg) pigs were allocated to either cinnamon (0 vs. 1.5%) or HS (thermoneutral (TN) vs. HS) conditions in a 2×2 factorial design. All pigs were acclimatised to diets for 14 d before TN (20°C) or cyclic HS (35°C 9AM-5PM/ 28°C) for 7 d. Respiration rate, rectal temperature and skin temperature were monitored 5x daily and an intravenous glucose tolerance test (IVGTT) was performed on day 7 to quantify insulin sensitivity. Contrary to our hypothesis, HS and therefore cinnamon did not influence insulin sensitivity, as quantified by the glucose area under the curve. HS increased peak glucose concentrations during IVGTT, indicating reduced glucose clearance. Cinnamon supplementation in HS pigs returned peak glucose to TN levels, however this result requires further validation as cinnamon unexpectedly increased peak glucose under TN conditions (2.52 a , 4.07 b , 3.99 b and 2.85 ab for TN, TN+Cinn., HS and HS+Cinn., P<0.001). In absence of any improvement in rectal or skin temperature and respiration rate it appears that 1.5% cinnamon did not ameliorate HS. During HS panting can result in hyperventilation and respiratory alkalosis, which results in substantial blood buffering and urinary excretion of HCO 3-(P<0.001). Interestingly in this experiment HS resulted in urinary acidosis (P<0.001), indicating impaired renal function or HCO 3-deficiency in 7 d HS pigs. Implications: Insulin sensitivity, which has been shown to be affected by HS in shorter term models, was not influenced in a 7 d HS model. When coupled with apparent bicarbonate deficiency it appears that insulin sensitivity may be involved in regulating short-term responses to HS and that diets formulated to combat the effects of alkalosis may be beneficial for extended heat events.