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 increase in emulsifier inclusion rate in the diets (P < 0.05). In conclusion, the addition of emulsifier at a rate at least 250 mg kg-1 to moderate- or low-energy diets during the starter, growth, and finisher phases can enhance broiler chicken performance by improving the histological characteristics of small intestine and enhancing lipid digestibility.
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