Dietary L-threonine supplementation attenuates lipopolysaccharide-induced inflammatory responses and intestinal barrier damage of broiler chickens at an early age

This study was conducted to investigate the protective effects of L-threonine (L-Thr) supplementation on growth performance, inflammatory responses and intestinal barrier function of young broilers challenged with lipopolysaccharide (LPS). A total of 144 1-d-old male chicks were allocated to one of three treatments: non-challenged broilers fed a basal diet (control group), LPS-challenged broilers fed a basal diet without L-Thr supplementation and LPS-challenged broilers fed a basal diet supplemented with 3.0 g/kg L-Thr. LPS challenge was performed intraperitoneally at 17, 19 and 21 d of age, whereas the control group received physiological saline injection. Compared with the control group, LPS challenge impaired growth performance of broilers, and L-Thr administration reversed LPS-induced increase in feed/gain ratio. LPS challenge elevated blood cell counts related to inflammation, and pro-inflammatory cytokine concentrations in serum (IL-1 beta and TNF-alpha), spleen (IL-1 beta and TNF-alpha) and intestinal mucosa (jejunal interferon-gamma (IFN-gamma) and ileal IL-1 beta). The concentrations of intestinal cytokines in LPS-challenged broilers were reduced by L-Thr supplementation. LPS administration increased circulating D-lactic acid concentration, whereas it reduced villus height, the ratio between villus height and crypt depth and goblet density in both jejunum and ileum. LPS-induced decreases in jejunal villus height, intestinal villus height: crypt depth ratio and ileal goblet cell density were reversed with L-Thr supplementation. Similarly, LPS-induced alterations in the intestinal mRNA abundances of genes related to intestinal inflammation and barrier function (jejunal toll-like receptor 4, IFN-gamma and claudin-3, and ileal IL-1 beta and zonula occludens-1) were normalised with L-Thr administration. It can be concluded that L-Thr supplementation could attenuate LPS-induced inflammatory responses and intestinal barrier damage of young broilers.