Pham Tan Nha, Nguyen Van Thu and Preston T R 2008 Effects of different  levels and  sources of crude protein supplementation on feed intake, digestibility and nitrogen retention in swamp buffaloes compared to local cattle. Proceedings MEKARN Regional Conference 2007: Matching Livestock Systems with Available Resources (Editors: Reg Preston and Brian Ogle), Halong Bay, Vietnam, 25-28 November 2007 http://www.mekarn.org/prohan/nha.htm