The absorption of labelled molybdenum compounds in sheep fitted with re-entrant cannulae in the ascending duodenum

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.