1. Anatomy of the gastrointestinal tract;Hofmann,1988
2. Nutrient requirements of sheep,1985
3. Water requirements for livestock, 2000, Alberta Agriculture Food and Rural Development Extension Bulletin.
4. When is water good enough for livestock?;Bauder;Montana State Extension Bulletin,2000
5. Guyer PQ: Livestock water quality, University of Nebraska Extension Service Bulletin G79-46A.