Formerly Reader in Agricultural Biochemistry, University of Edinburgh, and Head of the Department of Agricultural Biochemistry, Edinburgh School of Agriculture
R A Edwards:
Formerly Head of the Department of Animal Nutrition, Edinburgh School of Agriculture
J F D Greenhalgh:
Emeritus Professor of Animal Production and Health, University of Aberdeen
As others suggested, those by VanSoest (although older) are really good. I also like DC Church's book The Ruminant Animal: Digestive Physiology and Nutrition (also older, but still good).
There are lots of test books you can follow for ruminant nutrition and it might also depends on your level of understanding and if you want to use as a reference book depends on your student level. However, you may be interested at:
Quantitative aspects of ruminant digestion and metabolism / edited by J. Dijkstra, J. M. Forbes,
Aug 12, 1994 - Among the subjects Peter J. Van Soest covers are nutritional constraints, mineral nutrition, rumen fermentation, microbial ecology, utilization of ..