The Role of Fiber in Ruminant Ration Formulation

Several livestock species have the ability to digest fiber via microbial fermentation and to obtain useful energy from this process. However, in ruminants, fermentation of fiber occurs prior to the small intestine (Figure 1). Thus, microbial protein that is produced, as fiber is being digested, is available for digestion to amino acids with subsequent absorption for use by the animal. Although horses and pigs can digest some fiber, fermentation of fiber takes place in the hindgut which, is after the site of active protein digestion and amino acid absorption. The objective of this paper is to explain how fiber is digested in the rumen, to review practical factors that affect fermentation of fiber in the diet of ruminants, and to explain the basis for recommendations for fiber in ruminant diets.