This study evaluated the effect of an emulsifier on the energetic values of lipids fed to yellow-feathered chickens and established prediction equations for the metabolizable energy (ME) of lipids fed with and without an emulsifier. One hundred and ninety-two Chinese yellow-feathered roosters [Wen's Yellow A; initial body weight (BW) = 2.37 ± 0.33 kg] were individually weighed, divided into four BW blocks, and randomly assigned within block to the 16 dietary treatments with replicates of three roosters. The diets consisted of a corn basal diet or the basal diet supplemented with 8% of corn oil (CO), soybean oil (SO), cottonseed oil (CSO), rice bran oil (RBO), palm oil (PO), modified palm oil (MPO), or lard were evaluated with or without an emulsifier (0.02% of diet) in an 8 × 2 factorial arrangement. Diets were fed for 8 d, with 4 d for adaptation to diets and another 4 d for excreta collection. There was an interaction between lipid sources and emulsifier on ME (apparent ME and N-corrected apparent ME) of the lipids (P < 0.05). Addition of 0.02% emulsifier had no effect on the ME of CO, SO, PO, or lard, but reduced the ME of CSO (P < 0.05) and MPO (P < 0.05), and tended to increase the ME of RBO (0.05 ≤ P < 0.10). There was a quadratic relationship between ME and concentration of stearic (C18:0) (P < 0.05) or linoleic acid (C18:2) (0.05 ≤ P < 0.10), and a linear function between ME and concentration of oleic acid (C18:1) or monounsaturated fatty acids (P < 0.05) in diets without emulsifier. The ME of lipids could be predicted by the concentration of C18:0 with C18:1 or with monounsaturated fatty acid without an emulsifier. With an emulsifier, the ME concentration was affected linearly by the concentration of myristic acid (C14:0), palmitic acid (C16:0), C18:2, polyunsaturated fatty acids, unsaturated fatty acids, saturated fatty acids, and the ratio of unsaturated to saturated fatty acids (U:S) (P < 0.05). Prediction equations for the ME of lipid were established on the content of C18:0, C16:0, C14:0, SFA, and U:S. These results indicated that the ME of RBO is positively affected by emulsifiers, but the ME of CSO and MPO declines with emulsifiers. These inconsistent results may be influenced by the relationship between ME and concentration of fatty acid across sources of dietary lipids.
Keywords: chicken; emulsifier; lipid; metabolizable energy.
Considering that commercial diets generally contain 3% to 8% added lipids to provide up to 20% metabolizable energy (ME) in broiler diets, the addition of emulsifier in diets was believed to improve the digestibility of fat. In this experiment, seven sources of lipid with or without emulsifier addition were evaluated for ME in yellow-feathered broilers. Without emulsifier addition, ME values were observed highest for cottonseed oil [4,129 kcal/kg∙ dry matter (DM)] and lowest for rice bran oil (4,036 kcal/kg∙DM) and lard (4,015 kcal/kg∙DM). With emulsifier addition, ME values were highest for soybean oil (4,177 kcal/kg∙DM) and lowest for modified palm oil (4,059 kcal/kg∙DM) and lard (4,024 kcal/kg∙DM). The emulsifier has a positive effect on the ME of rice bran oil, but the ME of cottonseed oil and modified palm oil declines with the addition of emulsifiers. These inconsistent results may be influenced by the relationship between ME and concentration of fatty acids across sources of dietary lipids. Lipids with high concentrations of unsaturated fatty acids are more easily emulsified and better digested than those rich in saturated fatty acids. Additionally, the concentration of C18:0 and C18:1 in lipids contributed to the main variance of ME prediction equation.
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