Increased Dietary Inclusion Levels of Lysine Are More Effective than Arginine in Supporting the Functional Status of the Gut in Growing Turkeys

SIMPLE SUMMARY: The concentrations of essential amino acids (EAA) in turkey diets are established in line with the recommendations of either the British United Turkeys (BUT) or the National Research Council (NRC), which, however, differ with regard to the dietary levels and ratios of important EAA, including lysine (Lys), arginine (Arg) and methionine (Met). For instance, the dietary Arg:Lys ratio in turkey diets recommended by the BUT is approximately 2–5% higher than that recommended by the NRC. Similarly, the lowest and the highest values of the Met:Lys ratio recommended by the BUT exceed those recommended by the NRC by around six and three percentage points, respectively. The above differences may appear to be relatively small, but they raise concerns in the turkey production sector due to their potential impact on both feed cost and bird physiology. Since the turkey sector has grown rapidly in the past decade, a further understanding of the EAA needs of birds is essential to achieving high growth rates and maintaining a profitable and sustainable production. ABSTRACT: Arginine (Arg) and lysine (Lys) may be important for the overall health of turkeys. The aim of this study was to determine whether low (consistent with the guidelines) and high (10% higher than recommended) levels of dietary Arg and Lys can modulate performance and the functional status of the gut. Female turkeys were allocated to four dietary treatments (two levels of Lys (low or high) and two levels of Arg (low or high)) for a 16 wk feeding period. The treatments did not affect turkey performance determined separately for four feeding phases and for the entire 16 wk experiment (p > 0.05). They had no significant influence on carcass yield, meat characteristics or the associated traits either (p > 0.05). High-Lys diets contributed to a decrease in cecal pH, a significant increase in the concentrations of short-chain fatty acids (SCFA) and a decrease in the concentrations of putrefactive SCFA and ammonia in the cecum. High dietary levels of both amino acids significantly enhanced the activity of cecal microbiota evaluated based on extracellular enzyme activity. These findings indicate that the higher dietary level of Lys was more effective in modulating the physiological status of the gut in turkeys than Arg.