Rumen microbial attachment and degradation of plant cell walls

The plant cell wall of forages is a complex entity of cellulose fibers found in a matrix of hemicellulose and pectins. Different microbial types including bacteria, protozoa, and fungi associate with plant cell walls during incubation with rumen fluid. Bacteria, the major degraders of the forage cell wall, often firmly attach to the forage cell wall before digestion. Encapsulated cocci and irregularly shaped or pleomorphic bacteria are the predominant types of bacteria that adhere to and degrade cell walls. Although certain bacterial types adhere to particular forages, no consistent association was found between digestibility and the type of adhering bacteria. Bacteria adhere to the more rigid forage cell walls and adhere, or are close to, the more easily degraded cell walls. Tissues delignified with potassium permanganate or treated with sodium hydroxide (to improve forage digestibility) show a loss of electron denseness. These tissues separate into individual cells, which at times appear as microfibrils in the cell walls. Research is needed on forages of higher fiber content to mitigate the barriers that limit the attack on forage cell walls by rumen microorganisms.