Sulphur-selenium studies in sheep I. The effects of varying dietary sulphate and selenomethionine on sulphur, nitrogen and selenium metabolism in sheep

Abstract

Sulphur, selenium and nitrogen metabolism were studied in Merino wethers fed for 35-day periods on semi purified diets in which the sulphur content was increased to either 0·07 or 0·20 % by the addition of sodium sulphate. At both levels of sulphur, additions of selenium as DL-selenomethionine increased the basal level of selenium (0· 02μg/g) to 0·06, 0·09 and 0·67 μg/g. Both levels of dietary sulphur supported positive sulphur balances but a reduction in sulphur intake per se resulted in a significant depression in dry matter digestibility (P < 0·05), apparent nitrogen digestibility (P < 0·05), nitrogen balance (P < 0·01), sulphur balance (P < 0·05) and plasma sulphate-sulphur (P < 0·001). Sheep fed the diet with 0·07% sulphur also had significantly higher plasma (P < 0·05) and wool (P < 0·01) selenium levels. Selenium balance was not affected by differences in sulphate-sulphur intake. Selenium balances (P < 0·001), plus the selenium levels in plasma (P < 0·001), and wool (P < 0·001) were significantly different at the different levels of selenium supplementation. A positive selenium balance was achieved when the selenium intake was approximately 37 μg/day, regardless of sulphur treatment. The validity of using plasma and/or wool selenium levels as indices of the selenium status of sheep is questioned. © 1977 ASEG.