Effects of a short‐term supranutritional selenium supplementation on redox balance, physiology and insulin‐related metabolism in heat‐stressed pigs

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Heat stress compromises the efficiency of pig production. Physiological responses to HS including reduced gut blood flow and increased core temperature both contribute towards disrupting the redox status and triggering oxidative stress (Cottrell et al., 2015). Oxidative stress may be associated with HS‐induced metabolic disorders. Heat stress has a direct effect on increasing fat deposition in pigs (Christon, 1988; Kouba, Hermier, & Le Dividich, 2001; Wu et al., 2016), which may be due to the inhibition of lipolysis or lipid mobilization (Pearce, Gabler et al., 2013). Although the mechanism is unknown, the elevated blood insulin that has been observed in the heat‐stressed ruminants may be a reason for the reduced lipid mobilization (Baumgard & Rhoads, 2012, 2013), as insulin is an antilipolytic hormone (Wray‐Cahen, Dunshea, Boyd, Bell, & Bauman, 2012). As oxidative stress can cause insulin resistance (Houstis, Rosen, & Lander, 2006), it may be responsible for the elevated insulin in heat‐stressed animals. Moreover, oxidative stress occurs in the tissues of heat‐stressed pigs (Liu et al., 2016; Montilla et al., 2014; Pearce, Mani et al., 2013). Therefore, oxidative stress may be involved in the pathophysiology of metabolic disorders in pigs during HS; thus, an alleviation of oxidative stress may normalize insulin action and lipid mobilization.
Selenium is incorporated into glutathione peroxidase (GPX) which is an antioxidant enzyme. The current nutrient requirements of swine (National Research Council 2012) recommend 0.2 ppm Se for growing pigs under thermoneutral conditions. However, as a nutritional strategy to reduce HS, it is unknown whether a short‐term supplementation with supranutritional amounts of Se before and during a heat event can alleviate physiology and oxidative stress in heat‐stressed pigs, as it does in sheep (Chauhan, Celi, Leury, Clarke, & Dunshea, 2014; Chauhan, Celi, Leury, & Dunshea, 2015). However, pigs are more insulin sensitive than ruminants (Dunshea & D'Souza, 2003; Pethick, Harper, & Dunshea, 2005), and a cautionary note is that supranutritional Se supplementation (0.5–3.0 ppm) can adversely impact on insulin homoeostasis in pigs (Liu et al., 2012; Pinto et al., 2012) possibly by inhibiting the expression and function of the proteins participating in the insulin signalling. Therefore, the aims of the study were to investigate the effects of dietary Se supplementation as a means of mitigating the physiological responses and oxidative stress, and to explore its role in insulin‐related metabolism in pigs exposed to HS. Our primary hypothesis was that supplementation with 1.0 ppm Se for 2 weeks before and during HS can mitigate physiological responses and oxidative stress in the heat‐stressed pigs with a secondary hypothesis that an alleviation of oxidative stress may normalize insulin action and lipid mobilization.
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