Ratriyanto , A.; Indreswari, R.; Sunarto. Effects of Protein Levels and Supplementation of Methyl Group Donor on Nutrient Digestibility and Performance of Broiler Chickens in the Tropics. Int. J. Poult. Sci. 2014, 13 (10), 575–581. https://doi.org/10.3923/ijps.2014.575.581.