Effect of different sources of selenium supplementation on immune function in pregnant and lactating ewes.

BACKGROUND: Selenium (Se) is an essential soil mineral that can be incorporated into animal feedstuffs. Because of a lack of soil Se in some regions, organic or inorganic supplementation strategies must be implemented to prevent deficiencies and promote optimal ovine health. Therefore, the objectives of this study were to assess how inorganic versus organic Se supplementation influenced ewe Se status and immune function during late gestation and postpartum. Dorset Rideau ewes (n = 110) were fed a Se deficient diet from gestation d 110 through postpartum d 49 and received one of four daily oral Se treatments diluted in 5 mL of sugar water: 0 mg Se, 0.3 mg inorganic Se, 0.3 mg organic Se, and 0.6 mg organic Se. Throughout the trial, the ewes received various immune challenges, including intramuscular immunizations with a novel antigen (ovalbumin; OVA) on trial d 0 and 10, an intradermal OVA challenge on d 20, and a lipopolysaccharide (LPS) endotoxin challenge on trial d 49. RESULTS: The organic Se treatment groups had higher serum Se concentrations on most trial days compared to the 0.3 mg inorganic and control groups (P < 0.05). No significant treatment differences were found for the dermal hypersensitivity response to OVA, anti-OVA antibody response, glutathione peroxidase activity, cytokine response, cortisol response, or rectal temperature (P > 0.05). However, 4 h post-LPS injection, the serum albumin concentration was significantly lower in the 0.3 mg inorganic group compared to both organic Se groups, potentially indicating a higher degree of inflammation in the ewes supplemented with the inorganic Se. CONCLUSIONS: The results of this study indicate that organic Se supplementation can promote a higher Se status in ewes over time, but Se supplementation during this study period did not affect tested immunological parameters. This lack of difference in immune responsiveness between groups may be due to an absence of true serum Se deficiencies in the Se-deficient group or the levels of Se supplementation being insufficient to significantly improve immunocompetence.