Digestible methionine + cysteine:digestible lysine ratio in diets for broilers submitted to inflammatory challenge

Abstract

To estimate the ideal digestible (dig) Methionine (Met) + Cysteine (Cys):dig Lysine (Lys) ratio for broilers submitted or not to lipopolysaccharides (LPS) (E. coli) inflammatory challenge, 384 thirteen-day-old male chickens were distributed in a 4 x 2 (four ratios x with or without challenge) factorial completely randomized design, with eight replicates per treatment and six chickens per experimental unit (EU). The unchallenged birds received an application of saline solution (SS). The experimental diets were formulated to meet nutritional recommendations except for the dig Met + Cys levels, which varied according to the treatments. To obtain the experimental diets, a ration with a ratio of 0.69 dig Met + Cys:dig Lys was initially prepared, and later a diet with a ratio of 0.84. These rations were mixed in the appropriate proportions to obtain diets with ratios of 0.74 and 0.79. Parameters evaluated at 21 days of age included broilers’ performance, specifically weight gain (WG), feed intake (FI), and feed conversion ratio (FCR). Further parameters were jejunum mRNA content of nuclear factor kappa-B (NF-Κb), glutathione peroxidase (GPX), superoxide dismutase (SOD), glutathione synthetase (GSS), methionine adenosyltransferase (MAT2), cystathionine β-synthase (CBS), relative weights of liver and spleen, and dual-energy x-ray absorptiometry (DEXA) estimated fat mass (%) and lean mass (%). The differences were considered significant at an alpha level of 0.05. A linear regression model was used to evaluate the effects of the dig Met + Cys:dig Lys ratio on the evaluated parameters. There was no interaction (P > 0.05) between the inflammatory challenge and the increase of dig Met + Cys: dig Lys ratio for WG, FI, FCR, the relative weight of liver and spleen, and mRNA content of NF-Κb, GPX, SOD, GSS, MAT2, and CBS. The different ratios had no significant effect (P > 0.05) on the same data. However, there were significant differences (P < 0.05) between challenged and unchallenged animals. Chickens that received an intraperitoneal application of LPS all had lower performance parameters, and the liver and spleen had heavier and lower expression of GSS than those that received SS. No significant differences (P > 0.05) were observed concerning DEXA estimated fat and lean mass. Thus, the lowest dig Met + Cys:dig Lys ratio, that is 0.69 (1.193% dig Lys: 0.823% dig Met + Cys), was sufficient to maintain the parameters evaluated. Keywords: Sulfur amino acids. Poultry. LPS. E. coli.