| Summary: | Climate change is associated with an increased frequency and intensity of heat waves, posing a threat of heat stress to pig production. Heat stress compromises the efficiency of pig production partly due to causing oxidative stress, intestinal dysfunction, and inflammatory responses. Superoxide dismutase is an antioxidant enzyme reported to reduce oxidative stress and inflammation. Therefore, this experiment aimed to investigate whether recombinant superoxide dismutase (<sub>r</sub>SOD) could ameliorate oxidative stress and inflammatory responses in heat-stressed grower pigs. Sixty-four female pigs (Large White × Landrace, 27.8 ± 1.65 kg, mean ± SD) were randomly allocated to a control diet (standard grower feed, CON) or the control diet supplemented with 50 IU recombinant superoxide dismutase (<sub>r</sub>SOD) for 14 days. After acclimation to the diet, pigs were then housed under thermoneutral (TN, 20 °C, 35–50% relative humidity) or cyclic heat stress conditions (<sub>C</sub>HS, at 35 °C: 9 a.m. to 5 p.m. and 28 °C: 5 p.m. to 9 a.m., 35–50% relative humidity) for 3 days. Heat stress increased respiration rate (RR), skin and rectal temperature (RR and RT) (<i>p</i> < 0.001 for all), and reduced plasma thyroid hormone concentration (<i>p</i> < 0.001). The amount of oxidized glutathione (GSH:GSSG) was increased in the jejunum and ileum of <sub>C</sub>HS pigs. In the jejunum, <sub>r</sub>SOD also increased the amount of oxidized glutathione in both TN and <sub>C</sub>HS pigs, without any change in endogenous SOD activity. In the ileum, <sub>r</sub>SOD prevented increases in oxidized glutathione formation in the <sub>C</sub>HS pigs only. Taken together, this may reflect increased oxidative stress in both the jejunum and ileum in <sub>C</sub>HS pigs. Alternatively, <sub>r</sub>SOD increased the conversion of reduced to oxidized glutathione independently of <sub>C</sub>HS, possibly reflecting an increased overall SOD activity due to the addition of exogenous SOD. In conclusion, the use of in-feed SOD enzymes at a dose of 50 IU/kg may be a useful strategy for preventing oxidative stress in pigs.
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