Abstract
Heat stress is an increasing concern in poultry industry as it can cause a rise in the body temperature of chickens. Recently, we reported that l-citrulline (l-Cit) is a potential hypothermic agent that could improve thermotolerance in chicks. However, synthetic l-Cit has not yet been approved for inclusion in animal diets. l-Cit was first isolated from watermelon. Watermelon rind (WR), an agricultural waste product, contains more l-Cit than the flesh of the fruit. In the current study, the chemical composition and l-Cit content of WR dried powder (WRP) were determined. WRP was mixed with water at a ratio of 4:5 (wt/v) to make WRP mash, and then mixed with a commercial starter diet to prepare a 9% WRP mash diet. The WRP mash diet was fed to 3- to 15-day-old chicks and daily food intake, body weight, and changes in rectal temperature were measured. At the end of the experiment, blood was collected from the chicks to analyze plasma l-Cit and other free amino acids. The chemical analysis of WRP revealed a variety of components including 19.1% crude protein. l-Cit was the most abundant free amino acid in WRP (3.18 mg/g). Chronic supplementation of the WRP mash diet significantly increased compensatory food intake, plasma l-Cit, l-ornithine, and l-tyrosine in chicks. WRP mash diet did not affect the body temperature of the chicks. In conclusion, WRP mash diet supplementation increased plasma l-Cit concentration in chicks. The increase in plasma l-Cit concentrations suggest that WR could be used as a natural source of l-Cit in chicks to ameliorate the adverse effects of heat stress.