Effects of heat stress and antioxidants (selenium or vitamin E) supplementation on oxidative status in growing pigs

Abstract Text:

Heat stress (HS) results in poor performance in growing pigs and is associated with increased oxidative stress (OS) due to imbalances between free radicals production and anti-oxidants system. Therefore the aims of this experiment were to investigate the effects of supplementation with anti-oxidants (selenium (Se) and vitamin E (VE)) on OS status and HS amelioration in growing pigs. Thirty-six gilts (Large White × Landrace, 28±3 kg) were fed control (0.24 ppm Se, 17 IU VE/kg, NRC 2012 recommended), or control plus Se (1.0 ppm Se yeast), or VE (200 IU VE/kg) diet for 14d, then housed in either thermoneutral (20°C, humidity 40%; TN) or HS (35°C, 09�:00h-17�:00h/ 28°C, 17�:00h-09�:00h, humidity 35%) conditions for 7d. Feeding was restricted and equalized at 2.5 times of maintenance requirement. Blood samples were collected at d1 and d7 during thermal exposure to evaluate OS by quantifying 1) derived reactive oxygen metabolites (d-ROM, Carratelli Unit/mL); 2) anti-oxidants markers: biological antioxidant potential (BAP, µM), oxy-absorbent capacity (OXY-abs, µM), thiols (SHp, µM), erythrocyte glutathione peroxidase activity (GPx, µmol·min^-1·mL^-1); 3) oxidative damage marker: advanced oxidized protein products (AOPP, µM). Leukocyte HSP70, HIF-1α, GPx-1 and GPx-4 mRNA expression was quantified by real-time RT-PCR. Results were analyzed using REML in Genstat 16^th with diet, temperature, day as fixed effects, and pigs as random model. HSP70 and HIF-1α expression are the markers of hyperthermia and hypoxia, and both were up-regulated by HS (P<0.04). However, against our expectation, free radicals production, as assessed by d-ROM decreased during HS (616 vs. 593, P=0.04). GPx activity and SHp levels were not affected by HS, but BAP (2865 vs. 2770, P=0.02) and OXY-abs (300 vs. 287, P=0.03) were reduced, indicating HS compromised anti-oxidants defense system. Oxidative damage occurred during HS as evidenced by increased AOPP (24.6 vs. 32.4, P=0.008). Selenium supplementation tended to increase GPx activity during HS (12.2, 12.4 and 15.4 for Control, VE and Se, P=0.07) independently of GPx gene expressions. Selenium also lowered d-ROM under TN conditions (656, 606 and 599, for Control, VE and Se, P<0.05), but not during HS. Overall, VE did not influence any of the parameters measured and Se did not affect BAP, OXY-abs or AOPP. In conclusion, HS triggered OS by compromising anti-oxidants defense system, but Se or VE supplementation did not mitigate HS-induced OS, although GPx activity was improved by Se.

Keywords: oxidative stress, heat stress, antioxidants