INFLUENCE OF THE GUT FLORA AND OF SOME GROWTH-PROMOTING FEED ADDITIVES ON NITROGEN-METABOLISM IN PIGS .2. STUDIES INVIVO

Analysing the gastrointestinal contents of 22 slaughtered pigs, it was found that about 10% and 25% of the non-protein nitrogen (NPN) in the small and large intestine respectively, consisted of ammonia derived from deamination of amino acids and from urea degradation. Also the decarboxylation of amino acids was important. Both deamination and decarboxylation processes were greatly reduced by nutritional levels (20 p.p.m.) of Virginiamycin and Spiramycin. From the analysis of the N and urea content of the urine it could be deduced that Virginiamycin and Spiramycin can enhance N retention in pigs. Digestibility experiments with re-entrant cannulated pigs on a semi-purified diet revealed that Virginiamycin (50 p.p.m.) increases (P < 0.15-0.30) the apparent ileal digestibility of nitrogen (+ 2.1%), lysine (+ 1.4%), glycine (+4.8%), valine (+ 2.2%) and methionine (+ 3.3%). Absorption experiments based on perfusion of a temporarily isolated loop (2m) of the terminal small intestine of the pig, demonstrated that Virginiamycin enhances the net absorption of free amino acids by about 9% (P < 0.05-0.001). Growth promotion by nutritional antibacterials can therefore partly be explained by an altered digestion, absorption and retention of N in the pig.