composition of intestinal microbiota. Selected strains of microorganisms, believed to possess beneficial effects on digestive processes or animal health are used. Enterococcus faecium and spore-forming Bacillus spp. are the most frequently utilized probiotic microorganisms for swine. Probiotics were established as a new category of feed additives in the EU about twenty years ago and at present, there are more than 40 preparations approved for animal nutrition. In the US, such products are usually marketed as direct-fed microbials. The modes of action of probiotics are not well characterized and
therefore various hypotheses have been suggested in the literature (Kelly, 1998; Simon et al, 2001): • Competitive adhesion of probiotic microorganisms to epithelial receptors may prevent the attachment of pathogenic bacteria (rational behind “competitive exclusion”); • Aggregation of probiotics and pathogenic bacteria; • Competition for nutrients between probiotic and undesired bacteria; • Increased synthesis of lactic acid and reduction of intestinal pH;
• Production of specific antibacterial substances; • Reduced production of toxic amines and decrease of ammonia level in the gastro-intestinal tract. • Beneficial effects on the intestinal immune system, an improved intestinal defence against viral infections.
Several beneficial claims have been established for microbial
probiotics, but it is not always possible to provide sufficient scientific evidence to back up these claims. They usually show only limited and variable growth-promoting effects and in general, the “probiotic effect” is not as consistent as is the case for AGP.
Prebiotics The concept of prebiotics was first developed and introduced by Gibson and Roberfroid (1995) in human nutrition. It is based on the feeding of certain non-digestible oligosaccharides in order to control or manipulate microbial composition and/or activity, thereby assisting in maintaining a beneficial microflora (Zimmermann et al, 2001). Initially, various oligosaccharides, which are natural constituents of plants, were considered as potential probiotic products for animal nutrition, such as fructo-oligosaccharides, xylo-oligosaccharides, isomalto-oligosaccharides, trans-galactooligosaccharides (TOS), mannan-oligosaccharides and some fructans (inulin, lactulose). Dietary inclusion levels of potential prebiotics are usually 0.1 to 0.5% and many suppliers intend to market them as feed ingredients, claiming selective regulation of intestinal microflora, reduction of pathogens and promotion of beneficial microorganisms (e.g. Bifidobacteria, Lactobacilli). Roberfroid (2007) revisited this concept in human nutrition and concluded, that only two dietary non-digestible oligosaccharides, namely inulin and TOS (a mixture of oligosaccharides derived from lactulose by enzymatic transglycosylation) fulfil all the criteria necessary for prebiotic classification. They include resistance to gastric acidity, to hydrolysis by digestive enzymes and to gastrointestinal absorption, fermentation by intestinal microflora and selective stimulation of the growth and/or activity of those intestinal bacteria that contribute to health and well-being. Unfortunately, the effects of such ingredients
on the performance of farm animals such as poultry and swine are not consistent.
Essential oil compounds Another group of feed additives showing a potential for the replacement of AGP are essential oil compounds, which are active ingredients present in various plants, and spices (e.g. thymol, carvacrol, eugenol). Due to their antibacterial activity they might be able to modify the composition of intestinal microflora and to exert beneficial effects on performance of poultry and swine. At present all active compounds are listed in the flavouring agent group under EU legislation. In poultry, several authors have reported an in vivo effect on microflora by specific formulations of EOC: Hume (2006) showed an overall modification of the microflora, Mitsch (2004) a reduction of Clostridium perfringens and Jang (2007) a decrease in
E.coli numbers in broiler ileo-cecal digesta. Additionally, increases in digestive enzyme production have been identified by Lee (2003) and Jang (2007). However, a positive impact on performance has seldom been reported with EOC alone. Instead, a combination of benzoic acid and EOC has recently been shown to improve the performances of broilers (Weber, 2012) and turkeys (Giannenas, 2014). Although the efficacy of EOC in poultry show promise, more research is required in swine to better understand the benefits of these essential oil compounds either alone or in combination.
Future innovative concepts Substantial research has been conducted over the past few years to evaluate the potential of alternative antimicrobial agents for replacement of AGP. Some natural compounds such as lactoferrin, lysozyme, bacteriocins and antimicrobial peptides appear to result in beneficial effects. Lactoferrin, isolated from bovine milk was evaluated as a potential feed additive in early weaned piglets and significant positive effects on performance parameters were observed at a 2000ppm inclusion level. However, due to its relatively high production costs, practical use in animal nutrition is currently not feasible. Lysozyme (1,4-beta-N-acetylmuramidase) is an enzyme exhibiting antibacterial properties. It is present at low concentrations in animal products such as milk, eggs and also in many tissues. Recently published results confirmed that dietary addition of lysozyme improved growth performance of young piglets and it could also be considered as an alternative to AGP. Bacteriocins and antimicrobial proteins have also attracted attention as potential substitutes, but some regulatory issues, particularly in the EU, in addition to their high production costs are factors that might prevent their practical application in the near future.
Summary The total ban on antibiotic growth promoters in the European Union since January 2006 has had a serious impact on both performance and health status of early weaned piglets. Recent developments concerning possible replacement of AGP by effective alternative products referred to as eubiotics are reviewed in this contribution, with the main emphasis on organic acids, probiotics, prebiotics and essential oils. Some innovative concepts, in particular the potential use of lactoferrin, lysozyme and bacteriocins are also discussed.
This article was originally published on DSM Feed Talks on 4 September 2018:
https://www.dsm.com/anh/
en.html
FEED COMPOUNDER JULY/AUGUST 2019 PAGE 35
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