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Plasma diethylsuccinate carboxylesterase activity in plasma was elevated within 7 days in 4 sheep which received 4 mg Cu per kg body weight in gelatin capsules daily for 100 days followed by the same amount of Cu as a drench until the haemolytic crisis commenced. Plasma aspartate amino-transferase and sorbitol dehydrogenase activities in plasma were not elevated in these animals until sixty days after the Cu treatment began. Activities of all 3 enzymes in the liver homogenates from copper-treated sheep were lower (P less than 0.01) than in control animals.

The absorption of labelled molybdenum compounds was studied in pairs of sheep exchanging digesta via re-entrant duodenal cannulae. Tri- and tetrathiomolybdate 99Mo were rapidly absorbed from the rumen to circulate in plasma in a protein-bound and in a TCA-insoluble form. The compounds were also absorbed from the small intestine although some breakdown was evident. Initially, molybdate was poorly absorbed from the rumen but after several hours the concentration of protein-bound, TCA-insoluble 99Mo increased in plasma. This provides evidence of rumen thiomolybdate synthesis. The results indicate that thiomolybdates are absorbed directly from the rumen and despite the sensitivity of the compounds to acid, some absorption from the small intestine occurs after passage through the abomasum. Rumen absorption could be a contributory factor to ruminant sensitivity to the effects of Mo compounds.