Microbial perspective on fiber utilization by swine.

Dietary fiber may contribute up to 30% of the maintenance energy needs of growing pigs. Higher energy contributions may be obtained from dietary fiber fed to sows, along with some improvements in reproduction, health, and well-being. As long as cereal grain supplies and high-quality protein supplements are abundant, the use of fibrous feeds for swine most likely will be limited. However, as the human demand for cereal grains increases, swine producers, especially those with reproductive animals, may be economically forced to incorporate alternative feedstuffs. These feedstuffs might include lignified plant cell wall material such as grasses and legumes, and feed-milling and distillery by-products that contain a high level of fiber residues. The microflora in swine large intestine will be able to adapt to these lignified forages and by-product feeds much better than the microflora in humans. Swine microflora contain highly active ruminal cellulolytic and hemicellulolytic bacterial species, which include Fibrobacter succinogenes (intestinalis), Ruminococcus albus, Ruminococcus flavefaciens, Butyrivibrio spp., and Prevotella ruminicola. Additionally, a new highly active cellulolytic bacterium, Clostridium herbivorans, has been recently isolated from pig large intestine. The populations of these microorganisms are known to increase in response to the ingestion of diets high in plant cell wall material. The numbers of cellulolytic bacteria from adult animals are approximately 6.7 times greater than those found in growing pigs. None of these highly active cellulolytic bacterial species are found in the human large intestine. Thus, the pig large intestinal fermentation of fiber seems to more closely resemble that of ruminants than that of humans.