Activity of Fiber-Degrading Microorganisms in the Pig Large Intestine

The large intestine is comparable to the rumen fermentation in many aspects; however, it is understood less well. Fiber in the form of cellulose and hemicellulose is one of the major substrates fermented in the large intestine. Various studies suggest that the pig can utilize fiber for growth, and up to 30% of its maintenance energy may be derived from volatile fatty acids produced in the large intestine. The total number of microorganisms in the pig large intestine do not change when a high fiber diet such as 50 or 80% alfalfa meal is fed. However, the fiber-degrading organisms increase and obviously replace others. The increase in fibrolytic bacteria normally coincides with an increase in enzyme activity (cellulase and xylanase), indicating that diet can be used to enhance fibrolytic activity. This is true for growing pigs and adult animals. The cellulolytic organisms in the pig, Bacteroides succinogenes and Ruminococcus flavefaciens, are similar to those in the rumen and are present at comparable numbers. This partly explains why adult pigs can maintain themselves by merely grazing on forage in pastures. Assuming other conditions are met, there is a significant potential for fiber degradation in the pig large intestine. Whether various genotypes such as the genetically selected obese and lean pigs have different abilities to degrade fiber is unknown. More work is required to understand the interaction of the fibrolytic organisms with the other organisms present in the large intestine, similar to that which has been done in the rumen, as well as the microbe-host interaction.