The effect of molybdenum on the conversion of sulphate to sulphide and microbial-protein-sulphur in the rumen of sheep

Abstract

1. [35S]sulphate was used to measure the apparent turnover of sulphate, sulphide and microbial-protein-S in the rumen contents of four sheep that were intraruminally infused with 10 g sodium sulphate/d alone, or together with 126 mg sodium molybdate (50 mg molybdenum/d).2. Infusion of molybdate increased the concentration of sulphate in rumen fluid from 2.2 to 7.2 μg S/ml and decreased the rate of reduction of sulphate to sulphide by 50%. Although the rate of sulphide production was slower, the concentration of sulphide in rumen contents was increased. A dual role for molybdate in the metabolism of sulphide in the rumen is suggested to explain these changes.3. In animals that were not infused with molybdate, only one-third of the S (3.0 g/d) that passed through the sulphate pool in rumen fluid was converted to sulphide, decreasing to one-sixth when molybdate was infused.4. The turnover of S amino acids in microbial protein was not significantly affected by molybdate. Only 52–57% of the S amino acid content of microbial protein was synthesized de novo by way of the sulphide pool.