Effect of supplemental dietary selenium on growing-finishing pig performance and hepatic and erythrocyte glutathione peroxidase activity

Ninety-eight Yorkshire x Duroc pigs were utilized in this study to determine the effect of six supplemental dietary levels of selenium on growing-finishing pig performance and erythrocyte and hepatic glutathione peroxidase levels in the pig. The pigs were fed a basal corn-soybean meal ration containing approximately 50ppb natural selenium or the basal ration supplemented with 25, 50, 75, 100, 125 or 150 ppb Se as sodium selenite. The pigs were weighed biweekly, feed was measured and performance data were calculated every two weeks during the trial. Blood samples were collected from eight pigs on each treatment after 70 days on experiment and at slaughter. Hemoglobin and percent packed cell volumes were determined at the time the blood samples were collected. Erythrocytes from all blood samples were prepared by washing twice with sodium-phosphate-saline buffer and then frozen at -20°C until they were analyzed for glutathione peroxidase activity. Liver samples were collected at slaughter and were stored frozen until the analysis for glutathione peroxidase could be conducted. The results of this study indicate that there were no significant differences due to treatment on the performance criteria or carcass data that were measured in this study. Erythrocyte glutathione and enzyme units of activity were not significantly affected by treatment at 70 days of this experiment. However, pigs receiving the basal diet without any added selenium had noticeably lower levels of glutathione and enzyme units of activity on the seventieth day of the experiment. This finding suggests that the basal control ration was possibly marginal to deficient in selenium and that the supplemental levels overcame the marginal deficiency. Erythrocyte glutathione peroxidase enzyme units of activity and enzyme units of activity per milligram of hemoglobin at slaughter were significantly (P<.05) affected by treatment. These differences were not linearly increased with increasing level of supplemental Se. No consistent trend was observed and the randomness of the values may be partially explained by the hypothesis of Mahan et al. (1977) who suggested that pigs during the finishing phase may require only 50ppb Se. Since the basal diet in this study contained approximately 50ppb natural Se, the addition of supplemental Se would not be expected to have a consistent linear effect on glutathione peroxidase activity. No significant differences due to treatment in hepatic glutathione peroxidase were observed in this study. The fact that pigs utilized in this study were not depleted of their Se reserves before the experiment was initiated and the hypothesis of Mahan et al. (1977) may explain partially the results obtained for hepatic glutathione peroxidase in this study.