Changes in bacterial populations in the colon of pigs fed different sources of dietary fibre, and the development of swine dysentery after experimental infection.

Swine dysentery (SD) is a disease which can be controlled by feeding a diet low in dietary fibre. The influence of source and inclusion level of dietary fibre both on bacterial populations in the colon, and on subsequent development of SD in pigs experimentally infected with Serpulina hyodysenteriae was evaluated. In Experiment 1, pigs were fed a low-fibre diet based on cooked rice and a animal protein supplement, or the same diet containing added insoluble (iNSP, fed as oaten chaff) or soluble (sNSP, fed as guar gum) non-starch polysaccharides, resistant starch (RS), or a combination of the last two (sNSP/RS). In Experiment 2, different levels of RS were added to the diet. With the base rice diet and with the addition of iNSP, the total number of colonic bacteria was low, the Gram-positive population predominated, S. hyodysenteriae did not colonize and SD did not develop. Synergistic bacteria (Fusobacterium necrophorum and Fus. nucleatum), which have been reported to facilitate colonization by S. hyodysenteriae, were found only among isolates from pigs fed the sNSP/RS diet, and these animals developed SD. Addition of RS to the diet increased total bacterial counts and stimulated growth of Gram-negative bacteria in the colon. In Experiment 1, this permitted colonization by S. hyodysenteriae, but not expression of SD. In contrast, in Experiment 2, this level of inclusion and two others allowed both colonization and development of SD. In conclusion, the addition of sNSP and/or RS to an otherwise protective rice-based diet generated changes in the large intestine microbiota which might have some influence on proliferation of S. hyodysenteriae and the development of SD.