SULPHUR METABOLISM AND EXCRETION STUDIES IN RUMINANTS: III. The Effect of Sulphur Intake on the Availability of Copper in Sheep

In Merino wethers, increasing the intake of cystine-S or inorganic SO,-S under steady state feeding conditions significantly increased ruminal sulphide concentrations and decreased the flow of soluble copper to the omasum. The curvilinear regression of soluble Cu outflow (y, mg/day) on ruminal S= levels (x, ,ug-ml) was y = 5.57 -2.36x+ 0.491x20.0333~3 (r = 0.95; P<O.OOl), but the flow of soluble Cu was not significantly correlated with the flow of protein from t h e rumen (r = 0.48). A highly significant depression in potentially available Cu occurred when the S-intake was increased from 0.6 g/day to 1.95 to 3.4 g/day but levels of ruminal SE greater than about 2pg S/ml did not further reduce this flow below approximately 1.75 mg soluble Cu/day.