Ruminants such as cattle, sheep and goats digest feed including forages and grains (plant materials) to obtain nutrients for their maintenance and production (e.g. milk and meat). Thus, ruminant production is strongly connected with feeding management and hormonal regulation for maintaining homeostasis in ruminants. Although ruminants digest feed in the digestive tract, ruminants themselves do not produce fiber-degrading enzymes. But bacteria, fungi and protozoa inhabiting the digestive tract, especially the rumen, are able to digest fiber, main components of plant materials, and produce short chain fatty acids and microbial proteins as rumen fermentation products. Since those products are absorbed and utilized by ruminants as nutrients, rumen fermentation should be appropriately maintained. Moreover, disturbance of homeostasis in ruminants might lead to low productivity of ruminants. Therefore, feeding system and homeostasis in ruminants should be properly managed. However, ruminant productivity sometimes decreases by some reasons. In order to escape low productivity of ruminants, this unit is carrying out studies on ruminant metabolism and rumen microbiology.