Effects of the ionophore tetronasin on nitrogen metabolism by ruminal microorganisms in vitro

The effects of tetronasin on ruminal protein metabolism were investigated in vitro using ruminal fluid from cattle receiving tetronasin in the diet, ovine ruminal fluid from animals not receiving tetronasin and pure cultures of proteolytic ruminal bacteria. Ruminal fluid from cattle receiving tetronasin in a predominantly barley diet had lower proteolytic (76% of control, P less than .10) and deaminative (58% of control, P less than .05) activities than controls after 42 d. The effect of deamination disappeared after 84 d, although the proteolytic activity remained lower (P less than .10) than that of controls. When tetronasin was added in vitro to ruminal fluid from sheep not receiving the ionophore, proteolytic activity (14C-labeled casein hydrolysis) was unaffected, but the rate of ammonia production from amino acids was decreased by 87% (P less than .01). Oligopeptide breakdown was inhibited to a lesser extent (21%, P less than .05). Dipeptidase activity (dialanine hydrolysis) was not affected. The addition of tetronasin to cultures of the ruminal bacteria Ruminobacter amylophilus and Bacteroides ruminicola had no influence on their protease, deaminase or dipeptidase activities. However, when the bacteria were adapted to grow in the presence of tetronasin, deamination of amino acids was severely inhibited (87 to 100%, P less than .01), even when tetronasin was absent from the incubation mixture. Tetronasin had no effect on the proteolytic activity of adapted cultures.(ABSTRACT TRUNCATED AT 250 WORDS)