Definition of Prebiotic: A prebiotic is a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth, activity or both, of one or a limited number of bacterial species already resident in the colon.
For a food ingredient to be classified as a prebiotic it must:
- be neither hydrolyzed nor absorbed in the upper part of the gastrointestinal tract
- be a selective substrate for one or a limited number of potentially beneficial commensal bacteria in the colon, thus stimulating the bacteria to grow, become metabolically activated, or both; and
- be able as a consequence to alter the colonic microflora toward a more healthy composition.
Prebiotics were defined in 1995 by Gibson & Rogerfroid.
Another term which is used is the combination of these products is synbiotics being a combination of a prebiotic and a probiotic.
The natural microbiota (natural bacteria populating the body, and in this instance the gastrointestinal tract) promote the adhesion multiplication and provide a stimulus to the innate, local and systemic immune system. It promotes the maturation of the intestinal lining. Influencing this population is an indirect way of maintaining the healthy development and function of the gastro-intestinal tract. The tract needs to provide a source of nutrients, a barrier to infection yet provide a diverse environment for beneficial bacteria which co-habit mutually and to provide a barrier to infectious pathogenic organisms.
Typical effects of a Range of Prebiotics
Colostrum is one of nature’s prebiotics and if it is absent in the calf’s natural diet leads to slower uptake by beneficial bacteria. These would normally exclude undesired bacteria (pathogens). In its absence there is also a lack of a proliferative stimulus on the bowel lining. Good bacteria through selective prebiotic stimulus and/or dietary fibre provide an immune stimulus to promote maturation changes and disease resistance in the bowel lining. Colostrum (and other prebiotics) also enable the ‘weedy’ rapid multiplying species to be superceded by beneficial bacteria. By about 7 days a healthy bacterial population is normally well established. In calves under stress this can be upset by a number of factors – for example – transport, inappropriate handling, driving up and down ramps, and a failure of colostrum transfer from cows and the presence of infectious diseases.
The Intestine as an Eco-System:
A frequently noted feature of both prebiotics and probiotics is that groups of animals which appear to benefit most from these supplements are those most under ‘stress’, or outside the normal range of function. (refer Timmerman et al, 2005)
The more beneficial species such Lactobacilli spp are frequently quoted to be most sensitive to stressors. They are also the species with the slower generation times.
A healthy eco-system (such as the large intestinal microbiota) is best served by complexity, exhibited by a range of (bacterial) life-forms. And in the young pre-weaned calf, the major organ associated with energy transfer is the intestinal tract, it is particularly susceptible to stress for this reason with reductions in health and productivity.
Interpretation of Trial Results:
Interpretation of the benefits of prebiotics (and probiotics) vary widely. Trials tend not to quantify the degree of severity of ‘stresses’. Interpretation of the potential benefits of probiotics relate to their ability to survive the adverse stomach conditions in-transit, to be stable inhabitants – retreatment every day or so is usually recommended, and species specificity to the animal being treated is considered essential. Sensitivity to temperature is another feature of probiotic bacteria.
Both groups of supplements may give results which indicate a ‘nil’ result particularly when conditions are less conducive to disease from the absence of ‘stressors’.
It is therefore important not to focus attention on nil results in trials, particularly where trial conditions are different from the practical farm situation. On farm, diseases are frequently endemic in both clinical and sub-clinical forms.
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