The effects of emulsifier blend (EB) supplementation of diets with various levels of metabolizable energy (ME) and crude protein (CP) on broiler performance, digestibility, gut morphology, and muscle fatty acid profile were investigated over a 42-d period. Diets were arranged factorially (2 × 2 × 3) and consisted of 2 levels of ME (normal [commercially recommended levels] and low [100 kcal/kg reduction in dietary ME]), 2 levels of CP and limiting amino acids (normal [commercially recommended levels] and low [95% of the normal CP level]), and 3 levels of EB supplementation (0, 1, and 2 g/kg of diet). A total of 1,200 one-day-old male broiler chickens (Ross 308) were randomly assigned to 12 treatment groups (5 pens/treatment with 20 birds/pen). Supplemental EB linearly improved (P < 0.05) final body weight, overall average daily gain, and feed conversion ratio, but the magnitude of the responses was greater in low-ME and low-CP treatments, resulting in significant ME × CP × EB interactions. Similarly, the inclusion of EB in the diet, particularly at 2 g/kg, increased the ileal digestibility of crude protein and crude fat, as well as the AMEn value (P < 0.05), but the response was greater at lower ME concentration, indicating significant ME × EB interactions. Additionally, there were CP × EB interactions (P < 0.05) for duodenal villus height and villus height/crypt depth ratio, indicating that the effect of EB on these responses was more marked at lower dietary CP levels. An increase in dietary EB levels was accompanied by a linear increase in the concentration of total saturated fatty acids and a linear decrease (P < 0.05) in the concentrations of total polyunsaturated fatty acids in both breast and thigh meat. In conclusion, the positive effects of EB supplementation, particularly at a dietary inclusion level of 2 g/kg, were clearly evident in broiler chickens fed with low nutrient diets (−100 Kcal/kg ME and/or −5% CP and limiting amino acids) in terms of growth perf
