Effects of low energy diets supplemented with emulsifier on growth performance, nutrient digestibility, and intestinal morphology of broiler chickens

•Dietary energy affects growth performance of broiler chickens throughout growth phases.•Dietary emulsifiers enhance intestinal function, nutrient digestibility, and growth performance.•Emulsifiers enhance growth performance and nutrient digestibility in broilers chickens, especially in low-energy diets.•Emulsifiers benefit broiler chickens’ growth, health, and nutrient digestibility in low-energy diets. This study was conducted to investigate the effects of adding an emulsifier to energy-deficient diets on growth performance, intestinal morphology, and nutrient digestibility in broiler chickens. A total of 540 one-day-old male broiler chickens were randomly assigned to a 3 × 3 factorial arrangement of treatments with 4 pens and 15 broiler chickens/pen for 6 wk. Nine treatments consisted of 3 inclusion rates of emulsifier (0, 250, and 500 mg kg-1) and the standard, moderate, and low energy concentrations [45 and 90, 60 and 105, and 75 and 120 kcal apparent metabolizable energy (AME)/kg less for the moderate- and low-energy concentrations than the standard energy requirements during the starter (d 0 to 10), grower (d 10 to 24), and finisher (d 24 to 42) phases, respectively]. The average daily weight gain (ADWG) and average daily feed intake (ADFI) were recorded in the starter, grower, finisher, and total rearing (d 0 to 42) phases and feed conversion ratio (FCR) was calculated. The AME, digestibility of crude protein (CP), lipid, and organic matter (OM) of experimental diets, were determined from d 5 to 10 and from d 35 to 40. Broiler chickens fed moderate- or low-energy diets containing emulsifier showed greater ADWG and LBW, than those fed the standard diets along with lower FCR, compared to the same diets without emulsifier (P < 0.05). Live body weight increased, while both ADFI and FCR decreased linearly and quadratically with an increase in emulsifier inclusion rate in the diets (P < 0.05). Broiler chickens fed moderate-energy diets with 500 mg emulsifier /kg or low-energy diets containing 250 mg emulsifier /kg had greater villus height compared to those fed other diets (P < 0.05). The addition of emulsifiers to diets led to a linear increase in villus height, epithelium height, and the villus height to crypt depth ratio (P < 0.05). In moderate- and low-energy diets, the inclusion of emulsifiers resulted in greater AME and digestibility of lipid and OM (P < 0.05). The AME and digestibility of lipid and OM increased linearly and quadratically with an i