Response of Meat Chickens to Arginine in Reduced Protein Diets

Published literature indicates that L-arginine (L-Arg), guanidinoacetic acid (GAA) and L-citrulline (L-Cit) can all provide arginine activity in broiler diets (Su and Austic, 1999; Dilger et al., 2013; DeGroot, 2018) and all are commercially available. GAA has been reported to have 77% arginine equivalence for feed conversion (Ringel et al., 2013). This study was conducted to determine the effect of arginine deficiency on performance in reduced protein diets and the efficacy of adding it back as either L-Arg, GAA or L-Cit. Day old male Ross 308 birds (n = 768) were assigned to 8 dietary treatments using a completely randomized design: normal protein (NP, CP levels of 24.9, 23.7 and 21.4% for starter, grower and finisher, respectively), reduced protein deficient in Arg (RP, CP levels 5% lower than those of NP diets for all feeding phases) and RP with 2 levels of L-Arg (238 and 476 g/kg), GAA (309 and 618 g/kg) or L-Cit (238 and 476 g/kg). Requirements for digestible amino acids were based on Ross 308 specifications. All diets were based on wheat, sorghum, soybean meal and canola meal, with enough meat and bone meal added to satisfy the requirement for available-P. Xylanase was included to the diets at 2000 BXU/kg. Feed and water were provided ad libitum throughout the study. Three feeding phases were applied: starter (d0 to 10), grower (d11 to 24) and finisher (d25 to 35) with 6 replicates of 16 birds (starting) per treatment in floor pens with wood shavings as litter. Compared to NP diets, birds fed RP diets had reduced feed intake (FI) (2607g vs. 3611g, P < 0.001), body weight gain (BWG) (1520g vs. 2607g, P < 0.001) and increased FCR (1.701 vs. 1.386, P < 0.001) from d 0 to d 35. Additions of L-Arg or L-Cit at both levels resulted in increased BWG (maximum 558g and 702g for L-Arg and L-Cit, respectively) and reduced FCR (maximum 0.242 and 0.215 points, respectively) compared to the RP diet (P < 0.05). Birds fed GAA had lower FCR (P < 0.05) but not higher BWG (P > 0.05) compared to the RP diet. Birds fed the high L-arginine and high L-citrulline levels had no difference in FCR compared to NP birds (P < 0.05). Those fed either level of GAA had lower BWG and higher FCR compared to NP (P < 0.05). The recommended level of GAA is 60g/kg feed. In this study, birds fed the lower level of GAA had higher FI (2879g vs. 2517g), BWG (1844g vs. 1642g) than those fed the high GAA level, suggesting possible toxicity of GAA at the higher level. The results of the current study indicate that reduction of 50 g/kg CP is excessive in practical Australian diets based on wheat, sorghum and MBM possibly due to deficiencies in phenylalanine and/or tyrosine or non-essential amino acids. Responses to added L-arginine and L-citrulline were large and significant in arginine deficient RP diets.

ACKNOWLEDGEMENTS: This project was funded by Poultry Hub Australia.