Dietary supplementation of glycine modulates inflammatory response indicators in broiler chickens

Three experiments were conducted to investigate the effect of dietary glycine (Gly) supplementation on inflammatory responses in broiler chicks fed a basal diet using maize and soybean meal as the primary ingredients. Inflammation-related processes following lipopolysaccharide (LPS) injection were examined by analysing plasma concentrations of nitrate plus nitrite (NOx) and ceruloplasmin (Cer) in experiments 1 and 2, or expression of several genes in the spleen and liver including IL-1 beta and -6, TNF-like ligand (TL)1A, inducible NO synthase, interferon (IFN)-gamma and toll-like receptor (TLR) 4 were examined in experiment 3. Growth performance was also determined following immunological stimulation by both LPS and Sephadex injection in experiment 2. In experiment 1, birds fed a diet supplemented with Gly at 10 or 20 g/kg showed lower responses in plasma NOx and Cer than birds fed the diet supplemented with Gly at 0 or 40 g/kg. In experiment 2, a similar effect of Gly supplementation at 10 g/kg on plasma NOx and Cer was observed when chicks were fed either an isonitrogenous diet with Gly or glutamic acid (Glu). Gly-supplemented diet-fed birds showed better growth performance than Glu-supplemented diet-fed birds. The splenic expression of inflammatory response-related genes in birds fed a diet supplemented with Gly at 10 g/kg diet was lower than that of birds fed the basal diet in experiment 3. These results suggest that dietary Gly supplementation modulates the inflammatory response partly through changes in the expression of pro-inflammatory cytokines such as IL-1, IL-6, IFN-gamma and TL1A.