Influence of nitrate and molybdenum on sulfur utilization by rumen microorganisms

Twenty-four hours in vitro incubations were used to study the effect of nitrate and molybdenum on sulfur utilization by rumen microorganisms. Sulfur was added as sodium sulfate or sulfide at .1, .2, .3, or .4% of the substrate dry matter. Cellulose digestion was an indicator of microbial growth. The addition of .1 to .4% sulfate or sulfide sulfur increased cellulose digestion over the conrol, the two sulfur sources being equal in promoting cellulose digestion. No differences in cellulose digestion were found between .1 and .4% added sulfur. However, the addition of .4 of .8% nitrate-nitrogen depressed cellulose digestion and increased the requirement for both sulfate and sulfide. Depression was greater with .8% nitrate-nitrogen. In the presence of nitrate, sulfide was superior to sulfate in promoting cellulose digestion. When 4 or 8 ppm molybdenum were added to the incubations, increasing concentrations of both sulfate and sulfide were required to obtain maximum cellulose digestion. Molybdenum additions increased both the sulfate and sulfide requirement for maximum cellulose digestion.