Comparison of metabolizable energy values of wheat, paddy, and brown rice in roosters determined by free-feeding and tube-feeding methods

The objective of this study was to evaluate the impact of the determination methods (free feeding [FF] and tube feeding [TF]) on the available energy of ingredients (wheat, paddy, and brown rice). A total of 101 adult Hy-Line Brown roosters (35 weeks old) with an initial body weight of 2.72 ± 0.21 kg were used, in which 96 roosters were randomly assigned to the FF group and TF group, and the remaining five birds were selected to determine the endogenous energy loss. Each group consisted of 12 dietary treatments. In the FF group, each diet treatment comprised 2 replicates with 2 birds per replicate and 4 replicates with 1 bird per replicate for each diet in the TF group. The 12 dietary treatments included a basal diet (BD) and 11 test diets, in which wheat, paddy, and brown rice replaced 30% corn, soybean meal, and wheat bran in the BD. The experiment was performed three times. There was a significant effect of source on apparent metabolizable energy (AME) and true metabolizable energy (TME) in paddy (p < 0.05). Results showed that AME in wheat, paddy, and brown rice measured by the FF method were greater than those values gained by the TF method (p < 0.05). The average AME and TME values were 3537, 3140, and 3893 kcal/kg dry matter (DM) and 3555, 3163, and 3933 kcal/kg DM for wheat, paddy, and brown rice, respectively, measured by the FF method. The means of AME and TME evaluated by the TF method were 3270, 2988, and 3764 kcal/kg DM and 3642, 3357, and 4135 kcal/kg DM for wheat, paddy, and brown rice, respectively. In conclusion, the determination method has a considerable effect on available energy, and the TF method underestimates the AME of ingredients.