Transmission of Selenium as Selenite and as Selenomethionine From Ewe to Lamb via Milk Using Selenium-75

Selenite and selenomethionine, both labeled with75Se and administered via the feed to lactating ewes, were compared as sources of selenium for suckling lambs. During a 2-week post-partum period,75Se levels in ewe blood serum and milk increased at a much higher rate when the ewe received selenite. For selenite administration, the colostrum caseins (β and γ), which contained low levels of cystine, had relatively low75Se specific activities; the β lactoglobulin and α lactalbumin proteins, which contained high levels of cystine, had high75Se concentrations. The radioselenium apparently was complexed as selenotrisulfide. For the selenomethionine treatment, radioselenium was incorporated to the greatest extent in the milk proteins which had the highest level of either methionine or total content of sulfur amino acids. In post-colostrum milk, most of the milk75Se activity (73–79%) was carried by the caseins regardless of maternal selenium treatment.75Se concentrations were appreciably higher in the serum proteins and tissues of the lamb whose dam received selenomethionine. The data indicate that the ewe made better use of selenite than selenomethionine for secreting higher levels of selenium in the milk. However, when the ewe was fed selenomethionine, the forms of selenium in the milk were more available to the pre-ruminant lamb.