A moderate inflammation caused by the deterioration of housing conditions modifies Trp metabolism but not Trp requirement for growth of post-weaned piglets

Deterioration of the environment in which piglets are housed after weaning induces a moderate inflammatory response and modifies tryptophan (Trp) metabolism that can, in turn, decrease Trp availability for growth. We hypothesised that a Trp supply above the current recommendations may be required to preserve Trp availability and to maximise the growth of pigs suffering from moderate inflammation. The aim of this experiment was to compare growth performance and plasma concentrations of Trp and some of its metabolites in piglets, suffering or not from moderate inflammation, when they were fed diets containing graded levels of standardised ileal digestible (SID) Trp, obtained with the addition of crystalline L-Trp to the same basal diet (15%, 18%, 21% or 24%, relative to SID lysine). Differences in inflammatory status were obtained by housing the pigs under different sanitary conditions. Forty blocks of four littermate piglets each were selected and weaned at 4 weeks of age. The experimental design consisted of a split plot where the housing conditions (moderate inflammation v. control) were used as the main plot and dietary Trp content as the subplot. Body weight gain and feed intake were recorded 3, 5 and 7 weeks after weaning. Blood was sampled 13, 36 and 43 days after weaning to measure plasma concentrations of Trp, kynurenine and nicotinamide (i.e. two metabolites of Trp catabolism) and haptoglobin, a major acute phase protein in pigs. There was no interaction between dietary Trp and inflammatory status, irrespective of the response criterion. Compared with control pigs, pigs housed in poor housing conditions consumed less feed (P < 0.0001), had a lower growth rate (P < 0.001), higher plasma concentrations of haptoglobin (P < 0.05) and lower concentrations of plasma Trp irrespective of the Trp content in the diet. Increasing the Trp content in the diet improved feed intake (P < 0.05), growth rate and feed/gain (P < 0.05), but did not prevent the deterioration of performance induced by moderate inflammation because of poor housing conditions. The results of this study suggest that an inflammatory response caused by poor housing sanitary conditions altered Trp metabolism and growth performance, but this was not prevented by additional dietary crystalline L-Trp.