MICROBIAL STRATEGIES IN THE RUMINAL DIGESTION OF CEREAL-GRAINS

The rate and extent of ruminal digestion of cereal grains depends on t he rate of passage and a number of complex interactions between cereal kernel tissues and rumen microorganisms. The pericarp of cereal grain s is resistant to microbial attachment and penetration. This structure must be fractured by mechanical processing or mastication for digesti on to proceed. The susceptibility of the exposed endosperm to digestio n depends on the species of cereal grain. Corn and sorghum contain den se protein in the horny endosperm region which surrounds starch granul es and resists microbial colonization and penetration. In contrast, th e floury endosperm region in these two grains, and the endosperm of wh eat and barley are rapidly colonized by a variety of ruminal bacteria. Primary colonizing bacteria produce end products which attract second ary colonizers to the site of digestion to form adherent multispecies microbial biofilms. With finely ground cereal grains microbial biofilm s form at a rapid rate and the excessive production of acid end produc ts can often lead to digestive disturbances. Substances that prevent m icrobial attachment or promote detachment can be used to regulate the rate of cereal grain digestion in the rumen. Future strategies aimed a t regulating the rate of cereal grain digestion in the rumen must incl ude an appreciation for the microbial processes involved in cereal gra in digestion.