L-theanine, a natural nonprotein amino acid with a high biological activity, is reported to exert anti-stress properties. An experiment with a 3 × 2 factorial arrangement was conducted to investigate the effects of dietary L-theanine on growth performance and immune function in lipopolysaccharide (LPS)-challenged broilers. A total of 432 one-day-old male yellow-feathered broilers were randomly assigned to 3 dietary treatments (control, antibiotic and L-theanine diets) with 2 subgroups of each (6 replicate cages; 12 birds/cage). Birds from each subgroup of the 3 dietary treatments were intra-abdominally injected with the same amount of LPS or saline at 24, 25, 26 d of age. Both dietary L-theanine and antibiotic improved (P < 0.05) the growth performance of birds before LPS injection (d 1 to 21). The effect of dietary L-theanine was better (P < 0.05) than that of antibiotic. Lipopolysaccharide decreased feed intake (FI) and body weight gain (BWG) from d 22 to 28 (P < 0.05), BWG and feed to gain ratio (F:G) from d 29 to 56 (P < 0.05), increased mortality in different growth periods (P < 0.05), elevated the levels of serum cortisol, α1-acid glycoprotein (α1-AGP), interleukin-6 (IL-6) on d 24 and 25 (P < 0.05), reduced immune organ indexes and contents of jejunal mucosal secretory immunoglobulin A (sIgA) on d 28 (P < 0.05). The decreased FI and BWG, as well as increased F:G and mortality in LPS-challenged birds, were alleviated by dietary L-theanine or antibiotic from d 29 to 56 and from d 1 to 56. Dietary L-theanine mitigated the elevated serum α1-AGP level on d 25, serum IL-6 concentration on d 24 and 26, and the decreased jejunal mucosal sIgA content on d 28 of the LPS-challenged birds. The results indicated that L-theanine had potential to alleviate LPS-induced immune stress in broilers.
Keywords: Growth performance; Immune stress; L-theanine; Lipopolysaccharide; Yellow-feathered broilers.