Influence of high-fiber diet on bacterial populations in gastrointestinal tracts of obese- and lean-genotype pigs.

Bacterial populations from gastrointestinal tracts of genetically lean and obese pigs fed a low- or high-fiber diet (0 or 50% alfalfa meal, respectively) were enumerated with rumen fluid media and specific energy sources. Total culture counts in rectal samples declined 56 (P greater than 0.05) and 63% (P less than 0.05) in lean and obese animals, respectively, 3 weeks after feeding the high-fiber diet. After 8 weeks, culture counts had risen and were similar to those obtained before alfalfa was fed (0 week). At slaughter, 12 to 17 weeks after feeding the high-fiber diet, total counts from rectal samples of lean pigs continued to rise and were 13% greater than the 0-week counts, whereas counts from obese animals declined 37% (P greater than 0.05). The number of cellulolytic bacteria in rectal samples of lean-genotype pigs fed the high-fiber diet increased 80 and 71% from 0 to 3 weeks and 3 to 8 weeks, respectively. This overall increases from 0 to 8 weeks in lean pigs was significant (P less than 0.05); however, these increases were not seen in obese pigs. These data suggest that the microflora is initially suppressed when exposed to a high-fiber diet and that later some adaptation takes place, apparently more so in lean than in obese pigs. When specific energy sources were used to delineate the distribution of different bacterial populations in the cecum, colon, and rectum, trends could be detected between high- and low-fiber diets. These data also support the concept that bacteria populations from different sites in the large bowel differ.