Nguyen Thi Hong Nhan, Nguyen Trong Ngu, Nguyen Thiet, Preston T R and Leng R A  2005: Determination of the optimum level of a soybean oil drench with respect to the rumen ecosystem, feed intake and digestibility in cattle; Workshop-seminar "Making better  use of local feed resources" (Editors: Reg Preston and Brian Ogle) MEKARN-CTU, Cantho, 23-25 May, 2005. Article #09a. Retrieved, from http://www.mekarn.org/proctu/nhan09a.htm