Sulfur Metabolism In Ruminants

Two in vitrostudies were conducted to determine the availability of several sources of sulfur. A sulfur concentration of 21.5 µg/ml of inoculum was not adequate to meet the needs of rumen microbes in the in vitrosystem used, while concentrations of 86.7 and 130.0 µg/ml were apparently inhibitory. A sulfur concentration of 43.3 µg/ml in the incubation medium resulted in the greatest protein synthesis. Sulfur from L-methionine resulted in the greatest microbial protein synthesis, whereas sulfur from the common sources of supplemental sulfur, sodium sulfate and elemental sulfur, was only 55.4 and 35.8% as effective, respectively. Calcium sulfate and ammonium sulfate were the most effective inorganic sulfur sources. Sulfur from hydroxy analog of methionine was poorly utilized for microbial protein synthesis. Relative availabilities of sulfur from the various sulfur sources for in vitroprotein synthesis were: L-methionine, 100.0%; calcium sulfate, 94.1%; ammonium sulfate, 93.0%; DL-methionine, 63.0%; sodium sulfate, 55.4%; sodium sulfide, 42.6%; elemental sulfur, 35.8% and hydroxy analog of methionine, 28.8%.