Simple SummaryBroiler chicken production, providing valuable food products, has also been responsible for ammonia emissions which can lead to environmental pollution worldwide. Besides its economic and animal health advantages, feeding low protein diets can decrease the ammonia emission of broiler production. Even though low-protein diets balanced for amino acids have been used in practice, the ideal energy supply of broilers fed low-protein diets is not known. Therefore, our goal was to determine an ideal dietary energy-to-protein ratio of low-protein diets which does not compromise the production traits and carcass composition of the broilers. Based on our results, the 1.5% crude protein reduction in the diet while maintaining dietary energy constant did not negatively affect the production traits, increased the nitrogen retention, the breast meat yield, and decreased the drip loss of breast meat. Furthermore, the lowest concentration of total-N and uric acid-N in the excreta was obtained when isocaloric diets were fed. Although the low protein diets with reduced energy content led to lower final body weight of broilers, they did not affect the carcass composition, breast meat quality, nitrogen retention, and excreta composition compared to the control diet.AbstractThis study shows the effects of feeding low protein (LP) diets with different energy-to-protein ratios were evaluated on the production parameters, carcass composition, meat quality, nitrogen retention, and excreta composition of broilers. A total of 576-day-old Ross 308 broilers were fed a control diet (C) and three LP diets containing 1.5% less crude protein than diet C for 41 days. The LP1 treatment was isocaloric with diet C, while the dietary apparent metabolizable energy corrected by nitrogen (AMEn) levels in the case of the LP2 and LP3 treatments were reduced by 1.5% and 3%, respectively. The LP diets were supplemented with six crystalline essential amino acids (AA) to meet the standardized ileal digestible AA requirements of broilers. The LP1 treatment did not affect the performance parameters of broilers and increased the breast meat yield, the nitrogen retention and decreased drip loss of breast meat and the total-N and uric acid-N nitrogen excretion of birds in comparison with the C group. Although the energy-reduced LP2 and LP3 diets resulted in lower final body weight, they did not affect the carcass composition, breast meat quality, nitrogen retention, and excreta composition of birds compared with the control treatment.