The influence of dietary sulphur, molybdate and copper on the absorption, excretion and plasma fraction levels of 99Mo in sheep.

The effect of increased dietary sulphur, copper and molybdate on the metabolism of 99Mo administered via the rumen or duodenum was examined. Duodenally administered 99MoO4= was efficiently and rapidly absorbed and excreted via the urine; dietary modifications did not alter this pattern although increased dietary S increased the excretion rate. The passge of 99MoO4= through the rumen led to chemical modification, so that, particularly at high S levels, most of the radioactivity remained in the feces; increased dietary Mo led to increased absorption whereas increased copper decreased absorption. Incorportion of radioactivity into the TCA insoluble plasma fraction was shown with increased dietary S and particularly when both dietary S and Mo were increased. The compatiblity of the results with the hypothesis of ruminal thiomolybdate formation and subsequent reaction with dietary or tissue copper is discussed.