MICROBIAL AND ANIMAL LIMITATIONS TO FIBER DIGESTION AND UTILIZATION

The ruminal microbial populations attack, degrade and ferment structur al carbohydrates in forage cell walls and thereby provide volatile fat ty acids and protein to the host animal, Microbial colonization of fib er is quite rapid; however, the rate and extent to which fiber is degr aded is determined to a considerable degree by factors such as microbi al accessibility to substrate, physical and chemical nature of the for age and kinetics of ruminal digestion, The physical and chemical natur e of forages can present a barrier to their complete digestion in the rumen, especially the association of lignin with polysaccharide consti tuents, Adhesin proteins allow bacteria with cell-bound enzymes to com e into intimate contact with their substrates, ensuring that the degra dation products are preferentially available. Research on various fibr olytic enzymes and cellulose binding domains may allow for the transfe r of novel genetic material to bacteria for enhancing the hydrolysis o f plant cell walls, Fungi may also play an important synergistic role in the ruminal digestion of forages by physically disrupting the ligni fied stem tissue, This allows the ruminal microbes greater access to t he plant stem and the digestible portions of the plant, New developmen ts in fiber utilization by ruminants are currently under investigation and include genetic manipulation of ruminal bacteria, chemical and bi ological treatments of forages, and manipulation of dietary inputs and feeding management.