Heat stress is associated with death and other maladaptions including muscle dysfunction and impaired growth across species. Despite this common observation, the molecular effects leading to these pathologic changes remain unclear. The purpose of this study was to determine the extent to which heat stress disrupted redox balance and initiated an inflammatory response in oxidative and glycolytic skeletal muscle. Female pigs (5–6/group) were subjected to thermoneutral (20 °C) or heat stress (35 °C) conditions for 1 or 3 days and the semitendinosus removed and dissected into red (STR) and white (STW) portions. After 1 day of heat stress, relative abundance of proteins modified by malondialdehyde, a measure of oxidative damage, was increased 2.5-fold (P < 0.05) compared with thermoneutral in the STR but not the STW, before returning to thermoneutral conditions following 3 days of heat stress. This corresponded with increased catalase and superoxide dismutase-1 gene expression (P < 0.05) and superoxide dismutase-1 protein abundance (P < 0.05) in the STR but not the STW. In the STR catalase and total superoxide dismutase activity were increased by ~30% and ~130%, respectively (P < 0.05), after 1 day of heat stress and returned to thermoneutral levels by day 3. One or 3 days of heat stress did not increase inflammatory signaling through the NF-κB pathway in the STR or STW. These data suggest that oxidative muscle is more susceptible to heat stress-mediated changes in redox balance than glycolytic muscle during chronic heat stress.

Heat stress (HS) is a major concern for the swine industry as it negatively impacts pig production efficiency. Also, heat related illnesses remain a serious concern for human health. HS pigs exhibit reduced feed intake and diminished growth rate, still, little is known about the molecular effects of HS on pig skeletal muscle. This study aimed to determine the extent to which HS disrupts redox balance in pig red semitendinosus (STR) muscle. Crossbred gilts were subjected to thermoneutral (TN; 20°C) or heat stress (35°C) conditions for 1, 3 or 7 days. To account for reduced feed intake in HS animals a group of TN animals were pair fed to mimic intake of 7 day HS animals. To assess redox imbalance in STR, nitrotyrosine and MDA, markers of oxidatively modified proteins, were measured by Western blots. Additionally, catalase activity, a major antioxidant enzyme, was measured. Nitrotyrosine was similar between all treatment groups; however, 1 and 3 days of HS decreased MDA content by 25% (P<0.05) in HS pigs compared to TN pigs, but recovered to TN levels after 7 days of HS. Catalase activity increased ~30% after 1 day of HS (P<0.05), though after 3 days of HS catalase activity was similar to TN. These results suggest that there is an initial antioxidant response to HS to alleviate free radical injury, however this response is not sustained. Supported by USDA/NIFA Grant No. 2011–67003‐30007.