Excretion of A Single Dose of Selenium in Sheep

The excretion of Se⁷⁵ via the feces and urine was studied in 30 sheep. Se⁷⁵-sodium selenite was injected subcutaneously, using three different doses ranging from a tracer dose to a therapeutic dose. By the intraruminal route the substance was given in a tracer dose and a therapeutic dose. Se⁷⁵-selenomethionine was injected subcutaneously and intraruminally in a tracer dose. Se⁷⁵-selenocystine was given intravenously in a dose higher than that regarded as a therapeutic dose.After intraruminal injection a higher percentage of the dose was excreted via the feces than via the urine. After the two highest subcutaneous doses the urinary excretion was significantly higher than the fecal excretion. After a high selenium dose the percentage eliminated via the urine was greater than after a low dose, whether the subcutaneous or the intraruminal route was used.The fecal and urinary excretion of Se⁷⁵ was of approximately the same order after injection of Se⁷⁵-selenomethionine and Se⁷⁵-selenocystine as after injection of the tracer dose of Se⁷⁵-sodium selenite.In 2 sheep, 1.4 per cent and 3.7 per cent, respectively, of a therapeutic dose were excreted via the bile in 48 hours.Less than 3 per cent of a subcutaneous dose was eliminated with the expired air in 24 hours.Exactly how much of a therapeutic dose is excreted within, for instance, 2 weeks is difficult to establish, as the treated animal’s selenium supply with the feed is not known. In the experiments reported here, however, approximately 64 per cent of a subcutaneous and 75 per cent of an intraruminal therapeutic dose were excreted over a two-week period.