Fate of cyst(e)ine synthesized by microbial activity in the ruminant caecum

Cyst(e)ine synthesized by microorganisms in the caecum of sheep was labelled following the infusion of Na2 35SO4 into the terminal ileum. [35S]Cyst(e)ine activity was detected in the faeces, but not in plasma or wool. Appreciable absorption of 35S, presumably in the form of sulphide, into the circulation occurred, and its presence in saliva was demonstrated. It was concluded that nutritionally negligible quantities of cyst(e)ine are likely to be absorbed from the ovine large intestine.