Influence of dietary arginine ratio on local and systemic inflammatory responses to lipopolysaccharide in broilers

Arg is an essential AA for chickens that has secondary functions beyond protein synthesis and accretion, including roles in innate immunity. Therefore, the objective of this study was to evaluate the effects of dietary Arg ratio on the local and systemic innate inflammatory responses of the broiler chicken. A total of 280 male chicks from a Cobb 500 line were fed a common diet for 2 wk before being fed 1 of 5 target dietary dArg:dLys ratios (0.77, 0.91, 1.05, 1.19, or 1.33) across grower (14 to 28 d) and finisher (28 to 42 d) phases. Birds were reared in battery cages and immune parameters evaluated over 39 to 42 d using a growing feather (GF) model. Specifically, the GF-pulps of broilers were intradermally (i.d.) injected with 10 μL phosphate buffered saline (PBS; 2 birds/diet, 12 GF/bird) as a vehicle control or 10 μL of lipopolysaccharide (LPS; 6 birds/diet, 12 GF/bird; 1 μg LPS/GF) to stimulate an inflammatory response. Blood and GF were collected at 0 (before), 6, 24, and 48 h after GF injection. GF-pulp and blood cell suspensions were analyzed for indicators of the local and systemic inflammatory response, including GF-pulp and blood leukocyte profiles, relative GF-pulp cytokine mRNA expression, and plasma alpha-1-acid glycoprotein (AGP) and nitric oxide (NO) concentrations. Data were analyzed by 2-way repeated measures ANOVA for blood or 2-way ANOVA for GF, with time and diet as main effects. Linear and quadratic contrasts of dArg:dLys ratio were also performed. Statistical significance was determined at P ≤ 0.05. The local (pulp) and systemic (blood) inflammatory response to i.d. injected LPS was marked by a linear increase in heterophils with increasing dArg with a drop or no effect on lymphocytes, leading to changes in heterophil to lymphocyte ratios (P < 0.05). On average, plasma AGP responded quadratically (P < 0.0001) to dArg:dLys ratio within a 2-fold range, while NO increased linearly (P < 0.0001) by 7-fold at 6 h post-injection. Relative mRNA expression of IL-1β, IL-6, and IL-8 in GF-pulps also responded in a dose-dependent manner (P < 0.05). These data indicate that the GF model may be sensitive for detecting differences in immune responses of broilers fed different dietary treatments, and that Arg can influence the selected indicators of the LPS-induced inflammatory response in broilers.