Differences in microbial activity of digesta from three sections of the porcine large intestine according to in vitro fermentation of carbohydrate-rich substrates

To determine whether faecal microorganisms can represent the entire large intestinal population, samples from caecum, mid-colon and rectum of three adult pigs were used for the in vitro fermentation of fructo-oligosaccharide (FOS), potato starch, wheat bran and oat hulls. The cumulative gas production technique measured fermentation kinetics and end-products such as total gas, NH3 and volatile fatty acids (VFA). There were significant differences in the fermentability of substrates, in terms of both kinetics and end-products. More relevant to this study, there were also differences between pigs in respect of total gas production, the rate of gas production (R-m) and VFA production. For large intestine sections, there were more VFA from mid-colon and rectal inocula compared with that from the caecum (p < 0.0001). Total gas, R-m and NH3 were highest for rectal, intermediate for mid-colon and lowest for caecal inocula. (p < 0.0001). It was concluded that, while faecal sampling might overestimate caecal fermentation, its use is valid for in vitro assessment of large intestinal fermentation. However, differences between pigs indicate that a mix of samples from several animals remains important. (C) 2004 Society of Chemical Industry.