Sulfur Source for in Vitro Cellulose Digestion and in Vivo Ration Utilization, Nitrogen Metabolism, and Sulfur Balance

Abstract The response in vitro of rumen bacteria to different sources and percents of sulfur was measured by the extent or rate of cellulose digestion. Sources of sulfur: sodium sulfate, calcium sulfate, dl -methionine, and methionine analog were equal at equal sulfur in their ability to promote cellulose digestion at 24 hr. The optimum was .16 to .24% sulfur. Sodium sulfate showed a slightly greater time-rate response than the analog for the 48 hr. Growing dairy steers were used to determine the in vivo effect of sodium sulfate, dl -methionine, or methionine analog on digestibility, nitrogen utilization, and sulfur balance. Methionine analog resulted in greater dry matter and acid detergent fiber digestibility. True sulfur absorption was not influenced by its source although methionine analog resulted in more absorbed sulfur being excreted in urine and less retained. The regression of Y=sulfur balance (mg/day/kg .75 ) on X=sulfur intake (mg/day/kg .75 ) yields: Y=.84X—79.9, r=.94, with 95 mg at Y=0 for growing steers. Supplemental sulfur was more available than that in the natural diet. Methionine analog resulted in greater absorption of nitrogen, and the sulfate gave lower urine-nitrogen excretion. All sources of sulfur increased nitrogen balance with the sulfate superior to the analog and to dl -methionine.