Protective Effects of Nutrients or Non-Nutrients on Oxidative Stress of Weaned Pigs

Oxidative stress is the result of an imbalance in pro-oxidant and antioxidant homeostasis, which leads to the generation of reactive oxygen species. In pigs, oxidative stress can be induced by consumption of oxidized feed constituents or environmental stress factors. It is one of major threats to animal welfare, productive performance and the quality of animal products. Thus, exogenous antioxidants has been commonly practiced in animal feed. Those antioxidants include many nutrients (i.e. vitamin E and selenium), as well as non-nutrients (i.e. phytochemicals) that do not contribute any nutritional values to animals. More research is definitely needed: 1) to explore more rational and standardized approaches to evaluate antioxidant activity in vitro, 2) to investigate the antioxidant activity of natural substances using in vivo animal models. Different in vitro methods have been applied to evaluate the antioxidant activity of bioactive components, including chemical-based methods, lipid peroxidation assay, and cellular-based antioxidant assay. The sensitivity of those assays is following the order: cellular-based assay > lipid peroxidation assay > chemical-based methods. Cellular-based assays account for update, distribution, and metabolism of bioactive compounds in cells, therefore, have been considered more physiological representative and cost-effective approaches in antioxidant measurements. Although large amounts of valuable information could be provided by in vitro tests, in vivo animal trial is still highly recommended to validate the efficacy of tested antioxidants under different stress conditions. A diquat challenge model was developed to test antioxidant activity of a novel selenium product in weaned pigs. Diquat, a bipyridyl herbicide, could utilize molecular oxygen to generate superoxide anion radical and induce acute oxidative stress in animals. Selenium is a central component for the biosynthesis and functionality of selenoproteins; it plays an important role in antioxidant response and protection from infection and inflammation. In this model, we have observed that diquat injection reduced feed intake and growth rate and induced systemic inflammation and oxidative stress in weaned pigs. Supplementation of 0.3 mg/kg selenium enhanced antioxidant capacity of weaned pigs and counteracted the oxidative stress induced by diquat, as indicated by the increased antioxidant enzymes activities and reduced malondialdehyde concentration in plasma, liver, and brain. In conclusion, many nutrients and non-nutrients could provide protective effects to against oxidative stress in weaned pigs. A suitable model either developed from in vitro, in vivo, or their combination is needed to validate the potential antioxidants and decipher the underlying mechanisms.