Selenium Speciation Analysis Reveals Improved Antioxidant Status in Finisher Pigs Fed l -Selenomethionine, Alone or Combined with Sodium Selenite, and Vitamin E

Conditions associated with selenium (Se) and/or vitamin E (VitE) deficiency are still being reported in high-yielding pigs fed the recommended amounts. Here, the dietary effects of Se source (sodium selenite, NaSe, 0.40 or 0.65 mg Se/kg; l -selenomethionine, SeMet, 0.19 or 0.44 mg Se/kg; a NaSe-SeMet mixture, SeMix, 0.44–0.46 mg Se/kg) and VitE concentration (27, 50–53 or 101 mg/kg) on the antioxidant status of finisher pigs were compared with those in pigs fed non-Se-supplemented diets (0.08–0.09 mg Se/kg). Compared to NaSe-enriched diets, SeMet-supplemented diets resulted in significantly ( p < 0.0018) higher plasma concentrations of total Se (14–27%) and selenospecies (GPx3, SelP, SeAlb; 7–83%), significantly increased the total Se accumulation in skeletal muscles, myocardium, liver and brain (10–650%), and enhanced the VitE levels in plasma (15–74%) and tissues (8–33%) by the end of the 80-day trial, proving better Se distribution and retention in pigs fed organic Se. Injecting lipopolysaccharide (LPS) intravenously half-way into the trial provoked a pyrogenic response in the pigs followed by a rapid increase of inorganic Se after 5–12 h, a drastic drop of SeMet levels between 12 and 24 h that recovered by 48 h, and a small increase of SeCys by 24–48 h, together with a gradual rise of GPx3, SelP and SeAlb in plasma up to 48 h. These changes in Se speciation in plasma were particularly significant (0.0024 > p > 0.00007) in pigs receiving SeMet- (0.44 mg Se/kg, above EU-legislated limits) or SeMix-supplemented (SeMet and NaSe both at 0.2 mg Se/kg, within EU-legislated limits) diets, which demonstrates Se metabolism upregulation to counteract the LPS-induced oxidative stress and a strengthened antioxidant capacity in these pigs. Overall, a Se source combination (without exceeding EU-legislated limits) and sufficient VitE supplementation (≥ 50 mg/kg) improved the pigs’ antioxidant status, while doubling the allowed dietary organic Se increased the Se in tissues up to sixfold without compromising the animal’s health due to toxicity. This study renders valuable results for revising the current dietary SeMet limits in swine rations. Graphical Abstract