Selenium supplementation of grazing sheep. I. Effects of selenium drenching and other factors on plasma and erythrocyte glutathione peroxidase activities and blood selenium concentrations of lambs and ewes

摘要

Lambs or ewes grazing pastures in the low selenium region of New England in New South Wales nwere used to study the effects of selenium supplementation on blood and plasma levels of selenium nand glutathione peroxidase (GSH-px), and to assess the possibility of using GSH-px activity as an nindicator of selenium availability or selenium status in grazing sheep. nWhen lambs were drenched with selenium at 14 days of age there were large and rapid increases nin the initially low levels of plasma and erythrocyte GSH-px. The increase in plasnm GSH-px was ntransitory, and a second selenium drench administered to half the treated lambs at 42 days did not nevoke any further increase. Erythrocyte GSH-px activities of treated lambs remained elevated for na longer period than plasma GSH-px, and the second selenium drench extended the period of elevation. nAlterations in plasma GSH-px of adult ewes drenched with selenium were similar to those observed nin the lambs, but erythrocyte GSH-px activities increased much more slowly. The changes in plasma nand erythrocyte GSH-px were accompanied by significant alterations in plasma and whole blood nconcentrations of seleniun~. Increases in whole blood selenium, because of the plasma component, nwere much more rapid than those in erythrocyte GSH-px. nTransfer of ewes to a new grazing area with a different soil and pasture type led to similar changes nin plasma and erythrocyte GSH-px to those produced by selenium drenching. Small increases with ntime were also observed in the erythrocyte GSH-px activity of untreated ewes grazing the same npasture continuously. These changes were presumably the result of changes in the selenium content nand/or availability in the pasture. nIt was concluded that regular estimations of erythrocyte or whole blood GSH-px activities ncould be used as an indication of selenium availability and the selenium status of grazing sheep. nChanges in pasture and/or grazing area, and the fact that erythrocyte GSH-px activity of adult nanimals does not immediately attain a new equilibrium value when selenium intake alters must nhowever be taken into account.