RESUMEN
The objective of this study was to investigate the effect of dietary supplementation with 5-aminolevulinic acid (5-ALA) on the immune system, inflammatory response, and growth performance of broiler chickens. The levels of cluster of differentiation 3 (CD3) mRNA in the spleens of chickens gradually increased with dietary 5-ALA concentration, while the expression levels of interleukin (IL)-2 decreased. Mitogen-induced proliferation of splenic mononuclear cells and blood mononuclear cell phagocytosis in chickens fed 0.001 and 0.01% 5-ALA-supplemented diets were significantly greater than in chickens fed a basal diet (control). Plasma thiobarbituric acid reactive substance (TBARS) concentration gradually increased along with 5-ALA supplement concentration. These results provide the first evidence that the use of dietary 0.001 and 0.01% 5-ALA supplementation induces the T-cell immune system via mild oxidative stress in chickens. Three hours after Escherichia coli lipopolysaccharide-induced immune stimulation, the levels of mRNA encoding pro-inflammatory cytokines, such as IL-6 and tumor necrosis factor-like ligand 1A (TL1A), in chickens fed a 0.001% 5-ALA-supplemented diet were significantly lower than those in chickens exposed to other treatments. The plasma caeruloplasmin concentration in chickens fed a 0.001% 5-ALA-supplemented diet was significantly lower than in controls or in chickens fed diets supplemented with other concentrations of 5-ALA 24 h after injection of LPS. In addition, BW at 21 and 50 d of age was significantly higher in chickens fed a 0.001% 5-ALA-supplemented diet than in control chickens. The findings suggest that supplementation of diets with 0.001% 5-ALA could prevent the catabolic changes induced by immunological stimulation. These results show that 5-ALA might be useful as an immunomodulator to stimulate T-cells via mild oxidative stress in growing broiler chickens, thereby improving the growth performance.