1. Baker, A.J. (1973). J. Anim. Sci.36, 768–771
2. Beckmann, E. (1979). Gesamtsitzung des Kaiser Wilhelm Inst. für Chemie, Berlin-Dahlem, 275–285
3. Beckmann, E. (1919). British Patent151, 229
4. Donefer, E., Adeleye, O.A., Jones, T.A.O. (1969). Effect of Urea Supplementation on the Nutritive Value of NaOH-treated Oat straw. In: Advances in chemistry, G.J. Hajny, E.T. Reese, eds., series 95, Wash. D.C.: American Chem. Soc.
5. Eger, G. (1965). Arch. Mikrobiol.50, 343–356