Evaluation of selenium source on nursery pig growth performance, serum and tissue selenium concentrations, and serum antioxidant status

{"Background": "Selenium is an essential trace mineral for selenoproteins that function as antioxidant enzymes, protecting cells from oxidative damage. Selenium deficiency in pigs can cause sudden death, pale muscle, liver necrosis, mulberry heart disease, and damage to lungs and gastrointestinal tissues. The FDA regulates the maximum level of added dietary selenium at 0.3 mg/kg in complete feed for all stages of swine production. Different selenium sources\u2014inorganic (sodium selenite) and organic (selenium yeast, hydroxy-selenomethionine [OH-SeMet])\u2014may have bioavailability differences due to structural differences affecting absorption and storage. Previous studies have shown that nursery and growing pigs fed organic selenium sources had increased tissue selenium levels compared to those fed sodium selenite, without differences in growth performance. However, the differences between these products in diets formulated with corn and soybean meal from low-soil selenium regions fed to nursery pigs remained unclear. The objective of this study was to determine the effect of selenium source (sodium selenite, selenium yeast, and OH-SeMet) included at the legal limit of 0.3 mg/kg added selenium on growth performance, serum and tissue selenium concentrations, and serum antioxidant status of nursery pigs.", "Methods": "The study was conducted at a commercial research facility in north-central Ohio. A total of 3,888 weaned pigs (approximately 21 days of age; 337 \u00d7 1050, PIC; initially 6.0 \u00b1 0.23 kg) were placed in 144 pens with 27 pigs per pen. A total of 72 double-sided 5-hole stainless steel fence line feeders were used, each feeding 2 adjacent pens, with the feeder serving as the experimental unit. Pens were allotted to one of three dietary treatments in a randomized complete block design with blocking factors including sow farm origin, date of entry, and average pen bodyweight. There were 24 replicates per treatment. Diets were fed in three phases, all containing 0.3 mg/kg added selenium. Phase 1 was a common diet with sodium selenite fed from weaning to approximately 6.0 kg BW. Phase 2 and 3 experimental diets contained either sodium selenite, selenium yeast (Sel-Plex), or OH-SeMet (Selisseo). Feed samples were analyzed for selenium concentration using ICP/MS. One median-size barrow per experimental unit was selected for serum collection on days 0, 14, and 35. Serum selenium concentration, glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and thiobarbituric acid reactive substances (TBARS) were measured. On day 35, the same 72 barrows were euthanized for collection of loin muscle (10th rib) and liver tissue (right median lobe) for tissue selenium analysis. Data were analyzed as a randomized complete block design for one-way ANOVA using the lmer function in R. Feeder was the experimental unit. Tukey adjustment was used for multiple comparisons. Results were considered significant at P \u2264 0.05 and marginally significant at 0.05 < P \u2264 0.10.", "Key Results": "From days 0 to 14, pigs fed OH-SeMet had decreased ADFI (479 vs 490 and 490 g; P = 0.015) and ADG (422 vs 435 and 432 g; P = 0.003) compared to pigs fed sodium selenite or selenium yeast. From days 14 to 35, there was no evidence of difference in any growth criteria between treatments. From days 0 to 35, pigs fed OH-SeMet tended to have decreased ADG (567 vs 577 g; P = 0.066) compared to pigs fed sodium selenite. There was no evidence of difference in G:F, day 35 BW, percentage of injections, removal, or mortality between treatments. For serum selenium, there was a tendency for a source \u00d7 day interaction (P = 0.072). On day 14, pigs fed OH-SeMet had increased serum selenium (139 ng/mL) compared to pigs fed selenium yeast (122 ng/mL; P < 0.05). On day 35, pigs fed OH-SeMet had increased serum selenium (205 ng/mL) compared to both sodium selenite (184 ng/mL) and selenium yeast (184 ng/mL; P < 0.05). On day 35, pigs fed OH-SeMet had increased liver selenium (2.45 \u00b5g/g) compared to sodium selenite (1.97 \u00b5g/g) and selenium yeast (1.99 \u00b5g/g; P < 0.0001). On day 35, pigs fed OH-SeMet had increased muscle selenium (1.42 \u00b5g/g) compared to sodium selenite (0.81 \u00b5g/g) and selenium yeast (0.87 \u00b5g/g; P < 0.0001). For antioxidant status, there was a marginally significant increase in GSH-Px over time (P = 0.074) but no source \u00d7 day interaction or main effect of source. A source \u00d7 day interaction was found for T-AOC (P = 0.027), though no significant means separation was present. There was no evidence of source \u00d7 day, source, or day effects for TBARS (P > 0.10).", "Clinical Implications": "All three selenium sources fed at 0.3 mg/kg provided adequate selenium to meet nursery pig requirements, as all pigs had serum selenium concentrations within the normal range (80\u2013150 ng/mL suggested by Ullrey, 1987 and Mahan, 1991; above 120 ng/mL considered normal by Blood and Radostits, 1989). OH-SeMet demonstrated greater bioavailability, as indicated by significantly higher serum, liver, and muscle selenium concentrations compared to both sodium selenite and selenium yeast. However, this increased selenium reservoir did not translate into improved growth performance, health status, or antioxidant status under the conditions of this experiment. The study observed a reduction in early phase ADFI in pigs fed OH-SeMet, though the cause was not determined. The authors suggest that a higher selenium reservoir in tissue may benefit health and antioxidant status when pigs are under high oxidative stress, such as during disease challenges or gestation, but more studies are needed to confirm this. The study was limited by an unplanned Streptococcus suis challenge during the phase 2 period, which may have affected results, though pigs may have recovered before blood sampling on day 14."}