Effects of surplus dietary L-tryptophan on stress, immunology, behavior, and nitrogen retention in endotoxemic pigs.

The possible beneficial effects of surplus dietary Trp (+ 5 g Trp/kg diet) were investigated on factors related to stress, immunology, behavior, and N retention in post-weaning piglets (approximately 15 kg BW) challenged for 10 d with intravenous bacterial lipopolysaccharide (LPS; from Escherichia coli). Two diets fed restrictively (732 kJ NE/kg BW0.75/d) were compared: 1) basal diet (B; apparent ileal digestible Trp = 1.9 g/kg; a recommended level of Trp to warrant near-optimal growth in non-endotoxemic piglets) and 2) Trp enriched B (+ 5 g free L-Trp/kg) with 8 individually housed piglets per diet. Pooled salivary cortisol, but not plasma cortisol sampled at sacrifice, showed a tendency (P = 0.07) towards reduced concentrations in the Trp group (1.1 vs. 1.4 ng/mL; pooled SE = 0.1 ng/mL). Plasma C-reactive protein was reduced (P = 0.04) in the Trp group (0.9 vs. 5.0 mg/L; pooled SE = 1.3 mg/L), but haptoglobin, IL-6, tumor necrosis factor alpha, and LPS-induced fever were similar between the 2 dietary treatments. Physical activity related to approaching a human showed a tendency (P = 0.08) towards increased latency time in the Trp group (101 vs. 60 s; pooled SE = 16 s) but the times spent on standing, sitting, and lying were similar between dietary treatments. The ADFI, ADG (346 vs. 302 g/d; pooled SE = 14 g/d; P = 0.11), body N retention (11.6 vs. 11.0 g/d; pooled SE = 0.2 g/d; P = 0.18), and G:F (0.55 vs. 0.49; pooled SE = 0.03; P = 0.17) were not different between the Trp and B fed groups. In conclusion, surplus dietary Trp has limited impact on stress, immunology, behavior, and N retention in a pig model of systemic endotoxemia.