Amino Acid Availability of Isolated Rumen Microbes as Affected by Protein Supplement

Four Angus steers weighing 450 kg were used in a 4 × 4 latin square design to study the effects of different protein supplements (corn, soybean, fish and linseed protein) on bulk ammo acid composition and amino acid availability of rumen bacteria. The effects of different protein supplements on plasma amino acids, plasma urea nitrogen, rumen volatile fatty acids and rumen ammonia were also studied. Bulk amino acid composition of rumen bacteria was not significantly (P<.05) altered by protein supplement. Availability of rumen bacterial amino acids was estimated by measuring the concentrations of amino acids released from rumen bacterial protein upon in vitro pepsin-pancreatin digestion. The release of threonine, serine, glutamic acid, valine, methionine, phenylalanine, lysine and the total amino acids released varied significantly (P<.05) among treatments. Lysine had a (P<.01) greater release rate from bacteria obtained from steers fed soybean meal than from steers fed fishmeal. Plasma leucine and aspartic acid were significantly (P<.05) affected by protein source. Rumen acetate, propionate and ammonia-nitrogen levels varied significantly (P<.05) among treatments. These data indicate that the availability of certain amino acids to the ruminant animal can vary with the source of dietary protein.