Journal of Animal Production, Print ISSN: 2008-6776., Online ISSN: 2382-994X

Abstract Objective: The aim of this study was to determine the optimal arginine level in the diet of Japanese quails (Coturnix coturnix japonica) and to evaluate its effect on growth performance, feed efficiency, and carcass yield using broken-line and quadratic regression models. Method: 600 twenty-one-day-old Japanese quail chicks were randomly assigned to five treatments with digestible arginine levels of 0.75%, 1.00%, 1.25%, 1.50%, and 1.75%, with six replicates per treatment and 20 quails per replicate. The experimental diets were similar in all essential nutrients except for arginine. The experiment was conducted from day 21 to day 35, and during the experimental period, the effects of different arginine levels on body weight (BW) gain, feed efficiency, carcass yield, and the chemical composition of breast and thigh meat were measured. Results: Results indicated that arginine affected BWG and feed efficiency (P<0.05) of the quails, with the 1.25% arginine treatment being significantly different than the 0.75% and 1.00% treatments and having no difference with the 1.50% treatment (P<0.05). No treatment effect was observed for feed intake, suggesting that greater arginine levels improved the efficiency of feed utilization due to increased BW gain. Arginine requirement was estimated using both broken-line linear and quadratic regression models, with the broken-line linear model with a single slope identifying breakpoints at 1.15% for BW gain and 1.21% for feed efficiency, whereas the quadratic broken-line model predicted breakpoints at 1.30% and 1.29%, respectively. The quadratic regression model predicted that the highest BW gain occurred at 1.37% arginine and the highest occurred at 1.36% arginine. For carcass yield, the 1.25% arginine treatment yielded the highest carcass yield on day 35, which was significantly different than the 0.75% and 1.75% treatments. Both broken-line and quadratic regression models suggested that the optimal level for carcass yield was 1.12% and 1.26% and 1.32% arginine, respectively. Conclusions: The results of this study indicate that broken-line linear and quadratic regression models can be used to accurately estimate the arginine requirement in the diet of Japanese quails, and the optimal arginine level for improving growth performance and carcass yield in Japanese quails was found to be within the range of 1.15% to 1.37%, whichcan serve as a reference for improving dietary formulations in the quail farming industry and lowering feed costs.