Selenium retention in lambs fed diets supplemented with selenium from inorganic or organic sources

The objective of this study was to compare the effects of feed supplementation with equivalent selenium doses from sodium selenite (SS) and selenised yeast (Se-yeast) on Se absorption, retention, balance, and tissue deposition in young rams. Fifteen male lambs of the Slovak valashka breed (4 months old) were randomly allocated to three dietary treatments consisting of unsupplemented basal diet (BD) containing only background Se (0.07 mg/kg dry matter; DM) and two treatments based on identical BD supplemented with 0.3 mg Se/kg DM either from SS or from Se-yeast. After 14 weeks, no differences in blood Se levels were observed between rams fed the diet supplemented with SS or Se-yeast (0.30 vs. 0.31 mg/L, respectively), while lambs given BD showed significantly lower Se level (0.07 mg/L, P < 0.001). A similar response was found in the activity of blood glutathione peroxidase (GPx), with mean values for BD, SS and Se-yeast groups of 132.8, 931.7 and 954.4 U/g Hb, respectively (P < 0.001). The balance measurements carried out in week 12 showed significantly higher relative Se retention (% of Se ingested) in the rams given Se-yeast (58.3%) than in those fed the diet supplemented with SS (45.4%, P < 0.05), both differing from the control group (51.6%). The apparent Se absorption rate was significantly higher in the Se-yeast group (62.0%) than in the lambs treated with SS (49.6%) or in those fed the unsupplemented BD (52.9%, P < 0.001). Due to lower absorption rate the rams given SS had significantly higher faecal Se excretion than the Se-yeast fed animals, whereas no differences between the supplemented groups appeared in urinary Se excretion. The 14-week intake of Se-yeast resulted in significantly higher Se deposition in liver, muscles, heart, pancreas and spleen than that from SS. The highest tissue Se concentrations in each group were found in the kidney cortex (BD, SS and Se-yeast were 6.0, 12.9 and 11.9 mg/kg DM, respectively), whereas the respective levels in the kidney medulla were about four times lower (1.4, 2.7 and 3.1 mg/kg DM). The results demonstrate that in sheep the feed supplementation with Se from Se-yeast results in higher absorption of Se from the digestive tract and greater body Se retention than from SS. However, the inorganic source of Se was as effective as the organic one in supplying this essential trace element for the activity of specific selenoprotein GPx in blood.