Nguyen Ngoc Anh, Khuc Thi Hue, Duong Nguyen Khang and Preston 2011 Effect of calcium nitrate as NPN source on growth performance and methane emissions of sheep fed NaOH-treated rice straw supplemented with cassava foliage.  Workshop on Reducing Greenhouse Gas Emissions from Livestock and Soils (Editors: Reg Preston and Sisomphone Southavong). National Institute of Animal Science, Hanoi, 14-15 November 2011. httm://www.mekarn.org/workshops/GHG-CC/anh.grrc.htm