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Additives used to affect favourably the performance of animals in good health or used to affect favourably the environment are defined as zootechnical additives. In practical use two functional groups of zootechnical additives are of prime importance, i.e. digestibility enhancers and gut flora stabilizers. Within the first group mainly enzymes authorised for the use as feed additives having specificities for partial hydrolysis of cereal non-starch-polysaccharides (NSP-enzymes) and to release phosphorus from phytic acid (phytases).
NSP-enzymes are xylanases and β-glucanases which are used as single enzyme preparations or combined enzyme preparations in cereal based diets for chicken und piglets. The target subtrates of these enzymes are arabinoxylans (high contents e.g. in rye, triticale and wheat) and 1,3-1,4-β-glucans (high content in barley and oats). Soluble fractions of both NSP produce high viscosities in the intestinal contents of chicken ant to a smaller extent in piglets, which is the main reason for impaired performance and nutrient digestibility combined in severe cases with diarrhoea. Both, xylanases and β-glucanases are capable of reducing digesta viscosity and to eliminate partially or completely the antrinutritive effects of the mentioned NSP. Thus the main scope of the use of NSP-enzymes is to eliminate the deleterious effects of antinutitive substances. Modifications of the intestinal microbiota and their metabolic activity as well as modifications of gut functions are also involved in the overall effect of these enzymes.
In concentrate feed of plant origin approximately 70 per cent of phosphorus occur in form of phytic acid. Because animals do not secrete phytases into the intestinal tract, which are required for release of phosphoric acid groups from the molecule, the availabilta of phophorus from phytic acid is in monogastric animals restricted at a high degree. Addition of microbial phytases to feed of poultry and pigs is highly effective in improving phosphorus availability from plant material. Thus the main scope of the use of phytases is the increase of digestibility through action on the target feed material. In addition the digestibility of calcium and some trace elements is also improved. Furthermore, the by using phytases as feed additive, it is possible to reduce the inclusion of inorganic phosporus compound in the diet and to reduce considerably the phosphorus pollution into the environment, which is a serious problem in regions with high concentrations of animals.
Since the ban of antibiotics (growth promoters) as feed additives in the EU, selected micro-organisms (Probiotics) come to the fore as feed additives acting as “gut flora stabilizer”. The authorised micro-organisms for this application are of various origin e.g. strains of Enterocosccus faecium, spores of Bacillus spp. or strains of Saccharomyces cerevisiae. Although the majority of studies on the effectiveness of probiotics in piglets point towards improved animal prefomance, these effects are rarely significant and not consistent. However, when incidence of post weaning diarrhoea was recorded in almost all studies including different probiotic strains as significant reduction was observed. Studies on the mode of action of the probiotics Enterococcus faecium NCIMB 10415 and Bacillus cereus var. toyoi in piglets have shown, that both can be found within a short period in all segments of the intestinal tract. Both probiotics modified the intestinal microbiota, combined with a reduces identification frequency of various E. coli sero-pathovars. Furthermor it was shown, that transport kinstics of the intestinal mucosa and the immune status were involved in the response of the animals to the probiotic. Therefore, probiotics act primary as safety factors in a production system without antibiotic growth promoters rather than to replace antibiotics in terms of growth promoters.
Prebiotics are defined as selectively fermented feed ingredients that allow specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host wellbeing and health. Frequently studied substances with regard to these effects are e.g. inulin, fructooligosaccahrides or mannanoligosaccharides. Actually at present no such substances are authorized as feed additives in the EU but they are frequently discussed as alternatives to antibiotic growth promoters and are expected to act like “gut flora modifiers”. However, the effectiveness and the mode of action of prebiotics in farm animals is not well documented.