In vitro assessment of gastrointestinal tract (GIT) fermentation in pigs: Fermentable substrates and microbial activity

Recently, it has become apparent that GIT fermentation is not only of interest for ruminant animals, but also for monogastrics. While it is now widely accepted that the fermentation process and its resultant end-products can have important influences on animal health, little is known about the microbiological and immunological processes involved. In terms of animal health, most interest at the moment is focussed on those moments in animals’ lives when they are faced with sudden changes resulting in stress. The period of weaning in piglets is a typical example of this. The most easily accomplished and appropriate way to influence GIT fermentation processes is that of dietary intervention. This is reflected by the widespread interest in so-called pre- and pro-biotics. Given the complexities of the interactions occurring in the animal itself, it is hardly surprising that in vitro techniques are being widely used: firstly to examine potential substrates for their fermentability and possible inclusion in diets, and secondly, to assess changes in the microbial populations in response to these substrates. This paper will review the techniques currently in use for these two aspects of monogastric fermentation, and provide examples of their use

An in vitro batch culture method to assess potential fermentability of feed ingredients for monogastric diets

Interest in fermentation within the monogastric digestive tract is growing, particularly relative to animal health. This is of particular importance in relation to the forthcoming European ban on inclusion of anti-microbial growth promotors in animal diets. Fermentable carbohydrates are recognized as having an important role in fermentation in the monogastric digestive tract, and are often added to diets without having been examined for their actual fermentability, particularly in relation to the target animal. We describe an in vitro method to assess feed ingredients, as potential components of monogastric diets, which stimulate a positive fermentation (i.e., ones which will be well fermented and produce more short-chain fatty acids (SCFA) and less ammonia). This technique requires use of a batch culture containing the test substrate and an inoculum of appropriate origin. During fermentation, cumulative gas production is measured at regular intervals, as an indicator of kinetics of the reaction. When fermentation is complete, organic matter losses and end-products such as SCFA and ammonia, are measured. This paper illustrates use of the technique with 45 carbohydrate-based ingredients using faeces from unweaned piglets as inoculum. By assessing potential fermentability of a large number of ingredients, it is possible to make an informed choice as to which substrates are most suited for inclusion in a diet. By combining results with information about transit time, diets can be designed which should stimulate desirable fermentation along the entire digestive tract. In vitro fermentability is a potentially valuable characteristic in diet design, in order to stimulate microbial activity in the digestive tract

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 (RM) 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, RM 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. Copyright © 2004 Society of Chemical Industr