Influence of the gut flora and of some growth-promoting feed additives on nitrogen metabolism in pigs. I. Studies in vitro

Nine growing pigs (10–40 kg) were cannulated either in the duodenum or ileum or caecum and fed a dry-milk powder diet. These pigs were used as donors of fresh intestinal contents for short (4 h) incubation experiments. From the incubations of duodenal contents, it appeared that the bacterial activity was not important. In consequence, the antibiotic effects of Virginiamycin and Spiramycin were also negligible. During incubations of ileal contents, eventually supplemented with free amino acids, on the other hand, 20–30% of the amino acids were degraded by the flora either by deamination, with formation of ammonia, or by decarboxylation with formation of amines: histamine, putrescine, cadaverine, tyramine, phenylethylamine. Cadaverine, the decarboxylation product of lysine, was the most important amine detected. Both processes were severely decreased when the antibacterials Virginiamycin (50 p.p.m.), Spiramycin (50 p.p.m.), Carbadox (50 p.p.m.) and copper sulphate (200 p.p.m.) were present during the incubation of the ileal contents. The fermentation of caecal contents was characterized by a pronounced production of ammonia, slightly inhibited by Virginiamycin and Spiramycin.Testing the amino acid decarboxylation activity of the dominant flora (E. coli, S. faecalis, L. acidophilus and L. fermenti) in the small intestine of the pig, it was found that E. coli is the main producer of amines in the small intestine of pigs.We conclude that the gut flora of pigs has a measurable negative influence on protein digestion in the small intestine and that this effect can be overcome by feeding nutritional antibacterials.