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This study investigated the effects of dietary methionine (Met) sources and total sulfur amino acids to lysine ratio (TSAA:Lys) on broilers' growth and immune response challenged with lipopolysaccharides (LPS). 792 Arbor Acre broiler chicks at one-D-old were randomly assigned to a 2 × 3 × 2 factorial arrangement with two Met sources (DL-Met and DL-2‑hydroxy-4-methylthio-butanoic acid (HMTBA)), three TSAA:Lys ratio (0.58, 0.73, and 0.88) and two immunological states (LPS challenge or saline). The experiment was divided into 1-14 d and 15-28 d. At 15, 17, 19, and 21 d, broilers were intraperitoneally injected with LPS or an equal amount of saline. The results showed that LPS significantly decreased feed intake and body weight gain (BWG) of broilers at 15-21 d (P < 0.001). Met source and TSAA:Lys level (P = 0.064), Met source and LPS challenge (P = 0.080) both had a tendency of interaction effect on BWG. LPS significantly increased gene expression of inflammatory factors in the spleen and ileum, as well as serum inflammatory factors and acute phase protein levels (P < 0.05). Compared with the DL-Met group, HMTBA supplementation significantly decreased the gene expression of inflammatory factors in the spleen and ileum (P < 0.05), but up-regulated TLR4 expression level (P < 0.05), as well as increased serum levels of ovotransferrin (P = 0.047), α1-acid glycoprotein (P = 0.009), and IgA (P = 0.050). LPS increased ileal crypt depth (P = 0.001) and decreased villus height/crypt depth (P < 0.001). Compared with the DL-Met group, HMTBA treatment significantly increased Occludin and Mucin2 expressions in the ileum (P < 0.001). Further, HMTBA treatment also significantly increased the villus height (P = 0.021), villus height /crypt depth and goblet cell number (P < 0.001), and the short chain fatty acid production in the ceca (P < 0.05). When TSAA:Lys ratio was 0.73, HMTBA significantly increased broiler' BWG and helped maintaining the animal immune homeostasis by alleviating prolonged over-response of the immune system in broilers.
Gong et al. (Tue,) studied this question.