EFFECT OF RUMINAL MICROBIAL COLONIZATION ON CEREAL GRAIN DIGESTION

The objective of this study was to examine the microbial digestion and colonization of whole (W), halved (H) and quartered (Q) cereal grains within the rumen. Barley (Hordeum vulgare L.), maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), and wheat (Triticum aestivum L.) were placed in nylon bags in the rumen of a fistulated steer. In sacco DM disappearance (ISDMD) of W grain was lower (P < 0.001) than that of H or Q grain. Once sectioned, wheat was most susceptible to microbial digestion followed by barley, sorghum and maize, respectively. Scanning electron microscopy showed that microbial colonization of W grain was restricted to fractured areas of the pericarp. Fracturing of the pericarp is necessary to allow rumen bacteria to gain access to the rapidly digestible nutrients of the endosperm. Initial colonization (2 h) of the endosperm of H and Q grains by rumen bacteria tended to be between large starch granules. After 24 h of exposure in the rumen, the endosperm of barley, wheat and sorghum was colonized by a variety of rumen bacteria. In contrast, regions of the germ and horny endosperm in maize were not colonized. The sequential colonization of the endosperm, culminating in the establishment of complex microbial consortia, is required for the digestion of cereal grains. Key words: Cereal, rumen bacteria, digestion, processing, concentrate