Nutritional applications of arginine functionality to support broiler chicken health and performance.

Abstract

Four experiments were conducted to evaluate the effects of dietary dArg:dLys ratio on the performance and health of broilers subjected to different immunological, environmental, and pathogenic stress models. Experiment 1 used intradermal (i.d.) lipopolysaccharide (LPS) injections at 40 d to stimulate the innate immune response, and the local (tissue) and systemic (blood) inflammatory responses were evaluated at 0, 6, 24, and 48 h post-injection. Experiments 2 and 3 used a cyclic heat stress (HS) model in Ross 708 and Cobb 500 genotypes during the finisher phase to mimic the environmental challenges experienced by broilers in temperate zones during the summer and in tropical regions year-round. Experiment 4 utilized oral gavages of a 10-fold dose of a live coccidiosis vaccine at 15 d followed by ~10^7 CFU Clostridium perfringens at 19 and 20 d to replicate enteric challenge similar to what may be encountered by broilers in the field. In each experiment, dietary treatments included multiple (5 to 7) dietary dArg:dLys ratios that ranged from below to well above the current breeder recommendations. Linear and quadratic contrasts as well as regression analyses were used to evaluate dose-responses of dependent variables across increasing dArg:dLys ratios. In experiment 1, the local and systemic inflammatory response to i.d. injected LPS was dominated by an increase in heterophils (H) and a drop or no effect in lymphocyte (L) populations. On average, there was a linear increase in tissue and blood H with increasing Arg that also translated to a higher H:L ratio. Likely, this response was mediated by nitric oxide (NO), which increased linearly with increasing dArg:dLys ratio at 6 h post-injection. Concentration of alpha-1-acid glycoprotein (AGP) in the plasma and relative expression of IL-1β, IL-6, and IL-8 mRNA levels in tissue also responded in a dose-dependent manner to dietary Arg. In experiments 2 and 3, feed conversation ratio (FCR) was linearly improved during the finisher phase with increasing dArg:dLys ratio in both genotypes, but body weight gain (BWG) and feed intake were not affected. At 32, 38, and 46 d post-hatch, HS increased cloacal temperatures by approximately 1.6ºC, and dArg:dLys influenced body temperature dose-dependently in the Ross genotype only and not the Cobb. For processing characteristics, there were linear increases in chilled carcass and tender weights and yields and quadratic responses for breast fillet and total breast weights and yields in the Ross genotype. In the Cobb genotype, there was a quadratic response for fat pad weight and yield and linear increases in thigh and drum weights. In experiment 4, the enteric challenge significantly impaired growth performance during all periods, increased plasma NO and AGP concentration, and decreased ileal secretory IgA secretion. During the challenge recovery period (22 to 29 d), FCR of challenged birds improved linearly with increasing dArg:dLys, and increasing dArg:dLys ratio quadratically improved BWG and FCR of challenged birds during the grower phase and cumulatively. Dietary Arg did not significantly affect 22 d plasma NO or AGP concentration in this trial. For processing characteristics, feeding 1.29 dArg:dLys improved chilled carcass yield compared to birds fed 1.05 dArg:dLys. Overall, the results of these experiments indicate that increased dArg:dLys ratio beyond the current recommendations of 1.05 to 1.10 may be beneficial for improving broiler performance and health. This is likely due to the secondary metabolic functions of Arg, including synthesis of NO, that has diverse roles in supporting immunity and vasodilation.