Nitrogen Sources for Starch Digestion by Rumen Microorganisms

Tlle effectiveness of selected ammonium salts, amino acids, amides, and amidines as nitrogen sources for in vitro digestion of starch by rumen microorganisms has been compared with that of urea. Each nitrogen source was added to provide 3, 6, and 9 mg of nitrogen per 20 ml of an incubation mixture containing washed rumen microorganisms, minerals, buffers, and approximately 100 mg of purified corn starch. Ammonimn sulfate, ammonium chloride, ammonium acetate, and ammonium phosphate were equivalent to urea at all levels tested. Aspartic acid was inferior to urea, but significantly more effective than the other amino acids tested. Arginine, serine, methionine, valine, and glutamic acid additions resulted in moderate-to-slight increases in starch digestion. Lysine was not effectively utilized. Acetamide, propionamide, butyranfide, succinimide, malonamide, guanidine acetate, or aminoguanidine bicarbonate did not consisteutly stimulate starch digestion. High ammonia levels after 4 or 8 hr of fermentation were associated with stimulation of starch digestion.