Objective: To investigate the physiological effects of exogenous emulsifiers in broiler chickens that were fed tallow-incorporated reduced-energy diets over 35 days.Methods: A total of 256 Ross 308 one-day-old broilers (42.28 ± 0.16 g) were randomly allocated in a 2 × 2 factorial arrangement to 32 pens with eight chicks per cage. Birds were fed one of four dietary treatments as follows: (1) positive control (PCN; energy sufficient diet); (2) negative control (NCN; energy-deficient diet, -100 ME kcal/kg); (3) PCL (PCN plus 0.05% emulsifier) and ( 4) NCL (NCN plus 0.05% emulsifier). Growth performance was evaluated weekly whereas assessments for the carcass traits, digestibility, some blood metabolites, ileal morphology, and meat quality were measured on d 21 and d 35.Results: Birds fed the NCL diet had higher (P < 0.05) body weights, daily gains, daily feed intake, and improved feed efficiency over the entire 35-day period. Improvements (P < 0.05) for the ileal digestibility of crude fat, energy, and dry matter commensurate with longer (P < 0.05) villus heights were also observed with emulsifiers in the NCL and PCL diets. For the carcass measurements, only the liver weights were increased (P< 0.05) with emulsifiers in the supplemented groups. For blood metabolites, higher (P < 0.05) lipase levels were noticed with emulsifiers in the NCL and PCL diets. In addition, marginal reductions (P = 0.076; P= 0.095, respectively) were also noted with emulsifiers for the total cholesterol and triglyceride contents on d 35. Regarding meat quality, breast muscle yellowness was increased (P < 0.05) with emulsifier use in supplemented groups.

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