Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2005
Publication Date: December 1, 2005
Citation: Tiwary, A.K., Panter, K.E., Stegelmeier, B.L., James, L.F., Hall, J.O. 2005. Evaluation of the respiratory elimination kinetics of selenium after oral administration in sheep. American Journal of Veterinary Research. Vol. 66 No. 12 pp. 2142 - 2148. Interpretive Summary: Identification of physiologically important roles of selenium in immunity, reproduction, and productivity has increased the use of selenium for therapeutic and prophylactic purposes. Several reviews have been published regarding these aspects of supplemental selenium. However, because the margin of safety is low, there is considerable risk of selenium toxicosis caused by over supplementation or formulation errors. Selenium toxicosis also occurs naturally by consumption of plants containing selenium. The National Research Council recommends 0.3 ppm of selenium in the total diet of most animals. Organic forms of selenium such as selenomethionine (SeMet) and selenomethyl selenocysteine are the major plant forms of selenium, whereas the inorganic form selenium, namely sodium selenite, is the most common supplemental and injectable form. Because the primary clinical signs and lesions of sheep with selenium poisoning are associated with the respiratory system, it would be expected that the measured concentration of selenium in expired air would correlate with the severity of clinical signs and lesions. However, results of this study disproved that hypothesis. In fact, the selenium content in expired air of sheep receiving SeMet was significantly greater than that in sheep receiving sodium selenite, but sheep receiving SeMet did not have clinical signs. The potential for multiple selenium metabolites in expired air remains and may explain our findings. Future studies should address the various forms of selenium detected in expired air with time and how they correlate with toxicoses.
Technical Abstract: To evaluate the respiratory excretion and elimination kinetics of organic and inorganic selenium after oral administration in sheep 38, 8-12 week-old crossbred sheep (19 males and 19 females)were randomly allocated to one of 10 treatment groups with 4 sheep/group except group 5 which contained 2 sheep. Sheep in each group were administered selenium PO as a single dose of 0, 1, 2, 3, or 4 mg/kg as sodium selenite or selenomethionine. Expired air was collected and analyzed from all sheep at 4, 8, and 16 hours after administration. Clinical signs consistent with selenium intoxication were seen in treatment groups given sodium selenite but not in treatment groups given the equivalent amount of selenium as selenomethionine. However, a distinct garlic-like odor was evident in the breath of all sheep receiving 2 - 4 mg of selenium/kg. The intensity of odor in the breath did not correlate with clinical signs in affected animals receiving sodium selenite treatment. The concentration of selenium in expired air was greater in sheep receiving selenium as selenomethionine than sodium selenite. The concentration of selenium in expired air from sheep receiving high doses of selenium (3 and 4 mg of selenium/kg) was larger and selenium was expired for a longer duration than the concentration of selenium in expired air from sheep receiving low doses of selenium (1 and 2 mg of selenium/kg).