Relative bioavailability of seleno-compounds in the lactating rat.

Bioavailability of the organic forms of selenium (Se), selenomethionine (Se-methionine) and Se-yeast was determined relative to that of an inorganic form, selenite, in the lactating rat. A purified, casein-based diet without added Se was fed to nine groups of rats throughout pregnancy to produce a marginal Se deficiency. During lactation, groups (n = 8) were fed experimental diets containing either 0.1, 0.25 or 0.5 ppm Se as selenite, Se-methionine, or Se-yeast. On d 18 of lactation, tissue Se and glutathione peroxidase (GSH-Px) activities of dams and pups were determined. Based on slope-ratio analyses, the bioavailability of Se-methionine and Se-yeast was greater than that of selenite in both lactating dams and their nursing pups. The greater availability of organic Se to pup tissues may be a direct result of the greater concentration of Se in the milk of dams fed organic Se. A dietary level of 0.25 ppm Se as Se-methionine ensured maximal GSH-Px activity in both dam and pup tissues, but 0.5 ppm Se was necessary when selenite or Se-yeast was fed. These results indicate that, regardless of form, the National Research Council recommendation for growing rats of 0.1 ppm Se is not adequate to replete lactating dams and maintain maximal tissue GSH-Px in nursing pups.