**1. Introduction**

Traditionally, wheat grain is primarily used for human food consumption; the milling of wheat produces flour for human use and appreciable quantities of by-products for animal feeds. On average, wheat grain contains 65% starch, 15% protein, 14% fibre, 2.2% oil and 10% moisture [1]. With expansion of fuel ethanol production in North America and other places

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in the world during the last decade wheat grain has been used as second feedstock after corn for ethanol production due to its high starch content. Many different classes and types of wheat can be used for ethanol production. In general, soft wheats such as soft white and soft red classes are preferred to hard wheats because they contain higher starch content. Varieties with higher protein are less desirable, but may still be used when blended with one or more high starch varieties.

Increase of fuel ethanol production has resulted in a significant increase in the use of distiller grains in the diets of livestock animals, especially in ruminant feeding. Distiller grains have historically been used as a protein source for dairy cattle. Whereas, increased supply and reduced cost make it also a source of energy to replace grain. The distiller grain has comparable energy value to its original grain, high quality protein and high fibre content but highly digestible which is suitable for ruminant feed but not suitable for monogastric animals or poultry because of high fibre content. Wheat distiller grain is the major by-product of ethanol production when wheat grain is used as a substrate for ethanol production. In the last decade, research has documented the variation in chemical composition of wheat distiller grain, and its feed value as protein, energy or fibre source for dairy and beef cattle as well as small ruminant animals. Studies have frequently focused on comparing the feed value of wheat distiller grain to corn distiller grain and characterizing the impact of inclusion of these by-products on nitrogen and phosphorus excretion in manure. To our knowledge, there is no review article that has addressed these research findings, even though several review articles on the use of corn distiller grain in animal production and one book chapter on use of wheat distiller grain in pigs and poultry have been published [2, 3]. The objective of this chapter is to describe some recently developed knowledge and application of wheat distiller grain in ruminant animal diets.
