Ruminants can be considered as up graders of the quality of food when they are kept on feeds low in nitrogen and rich in structural carbohydrates such as cellulose. Many feeds and agricultural wastes of no value or unattractive to monogastric animals can be converted into tractive power, milk, wool, meat and offspring by ruminants. To attain levels of production, concentrates which are readily degraded and high in protein are being increasingly fed, which results in improper use of the ruminant, production losses and metabolic disorders due to unstable rumen fermentation. This is also associated with the fact that our domesticated cattle belong to a group of ruminants particularly equipped to deal with roughage. Most other ruminants in the group of the large roughage feeders are even superior to European cattle breeds in digesting poor roughage. When it would become necessary to increase the use of roughages and agricultural lignocellulose wastes in the near future, a large ruminal volume and a high salivation rate should be adopted as criteria of selection in breeding new cattle breeds.