Using Recombinant Superoxide Dismutase to Control Oxidative Stress in the Gastrointestinal Tract of Cyclic Heat-Stressed Pigs

SIMPLE SUMMARY: Global warming is increasing the impact of heat stress on pig production, particularly in tropical and subtropical areas. This impacts efficient pork production by increasing the prevalence of heat stress syndromes, partly due to oxidative stress, inflammation, and gut dysfunction. Hence, various strategies have been introduced to reduce the adverse effects of heat stress at high temperatures. Superoxide dismutase is an antioxidant enzyme that eliminates superoxide radicals and improves redox balance. Previous studies have shown that supplementation with superoxide dismutase reduces oxidative stress and inflammatory responses, but investigations into its effects on heat-stressed pigs are lacking. Therefore, this study aimed to investigate the effects of dietary supplementation with recombinant superoxide dismutase on oxidant status and inflammatory responses of growing pigs exposed to heat stress conditions. ABSTRACT: 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 ((r)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 ((r)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 ((C)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) (p < 0.001 for all), and reduced plasma thyroid hormone concentration (p < 0.001). The amount of oxidized glutathione (GSH:GSSG) was increased in the jejunum and ileum of (C)HS pigs. In the jejunum, (r)SOD also increased the amount of oxidized glutathione in both TN and (C)HS pigs, without any change in endogenous SOD activity. In the ileum, (r)SOD prevented increases in oxidized glutathione formation in the (C)HS pigs only. Taken together, this may reflect increased oxidative stress in both the jejunum and ileum in (C)HS pigs. Alternatively, (r)SOD increased the conversion of reduced to oxidized glutathione independently of (C)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.