The animal’s digestive system has an extremely important role in providing the necessary nutrients and their efficient utilization by the organism. It is known that only a healthy digestive tract can ensure the successful realization of the genetic potential in animals. The tendency is that from now on the role of antibiotics in maintaining gut health will continue to diminish. That imposes the need for future optimization of the biosecurity and animal nutrition, as well as the application of advanced technologies in the production and application of feed additives.

The animal feeding schedule needs to be optimized and balanced in such a way that they can maintain a stable microflora and good health status of the intestinal tract. Whether antibiotics are supplied as growth promoters or for the treatment of intestinal infections, their use must be significantly restricted in the coming years, while not compromising with intestinal health. Probiotics, prebiotics, synbiotics, phytobiotics, enzymes, organic acids, nucleotides, bioactive proteins and peptides, amino acids and some microelements are all feed additives, which have proven positive effect as modulators of the gut microecology. Their mechanisms of action on the gastrointestinal microbiota are complex, diverse and can be either direct or indirect.

E. Barba (2019) classifies the main mechanisms of action of feed additives, used for gut health improvement, in four groups:

1. Strengthening the immune response and the barrier function;
   
2. Reducing the pathogenic bacteria;
   
3. Stimulating beneficial microbiota;
   
4. Supporting the digestibility and utilization of nutrients.
   

Probiotics. The term probiotic is relatively new and Salminen S. (1996) determines them as foods, containing live bacteria, beneficial to health. Subsequently, many definitions have emerged, and they all come together to the understanding that probiotics, as preparations of living microorganisms that enhance endogenous microflora. In 2002 The World Health Organization officially accepted the following definition for the probiotics: “live microorganisms which when administered in adequate amounts confer a health benefit on the host” (WHO, 2002).

Currently, this is the most widely used and accepted definition, encompassing all applications of probiotics as live microorganisms, and is not restricted only to the intestinal homeostasis benefits. Thus, two key points are of paramount importance: 

1. Probiotic preparations should contain live microorganisms; 
2. The desired health benefits depend on the amount of the preparation administered.

Probiotics are living microorganisms, which are administered to the animals to colonize the digestive system, thus beneficially altering the intestinal microflora. Their mechanism of action is based on the competitive exclusion effect – limiting the attachment surface of unwanted microorganisms (Salmonella, Clostridia, coliform bacteria, etc.) and/or the antagonistic properties of probiotics against them. The effect of probiotics is somewhat similar to that of antibiotics, since in both cases it results in a favorable change in the gut microflora. In antibiotics, this is achieved by directly suppressing the unwanted microorganisms, while probiotics have more of an indirect effect via stimulation of the beneficial bacteria. 

Currently, the most commonly used probiotics in the animal breeding industry belong to the genera Bacillus, Lactobacillus, Bifidobacterium, Enterococcus and Saccharomyces. These probiotics have been shown to have the ability to enhance immune response, reduce populations of pathogenic bacteria, stimulate the beneficial microbiota, and aid digestion.

Although probiotic bacteria can survive passage through the stomach, they do not form permanent colonies in the body and need to be renewed. Therefore, they should be administered regularly in order to maintain the health benefits. Moreover, encapsulation may be necessary to protect the bacteria from stomach acids, ensuring they reach the intestines alive. Probiotics provide numerous benefits, including boosting immunity, particularly after infections and antibiotic treatment, inhibiting harmful bacteria, and regulating intestinal microflora.

Prebiotics. Prebiotics are defined as indigestible nutrients that favorably affect the host by selectively stimulating growth, activity or both of one or more beneficial bacteria in the gastrointestinal tract. Prebiotics are the “food” for probiotics. Prebiotics are nutrients that are not digested by digestive enzymes and are not utilized in the upper digestive tract. Thus, they reach the large intestine, where they ferment to short-chain fatty acids and stimulate the development and survival of beneficial microorganisms that are normally present there, or alternatively – provided with the feed. The most commonly used prebiotics in animal husbandry are mannan-oligosaccharides, fructo-oligosaccharides, inulin and lignocellulose. Prebiotics are used in birds and pigs because in ruminants they break down in the abdomen and do not reach the large intestine.

Synbiotics. Synbiotics combine probiotics and prebiotics to produce a synergistic effect that is superior to administering the two products separately.

Phytobiotics. These include aromatic plants (herbs and spices), plant extracts and volatile fatty acids. The main principle of action is based on the volatile fatty acids (thymol, carvacrol, etc.) and the polyphenols. Phytobiotics have been shown to be able to modulate the immune response as well as the intestinal microbiota (via antimicrobial action against pathogenic bacteria).

Enzymes. There can be no nutrients digestion and good utilization without enzymes. Enzymes are complex proteins produced by living cells that trigger chemical reactions in the body. Exogenous enzymes are added to the rations because they improve the utilization of the nutrients contained in the feed, as well as positively affect the gut microbiota profile. The feed contains cellulose, pectin substances, β-glucans, oligosaccharides and other substances that are not digested in the animal body by endogenous enzymes. The most common enzymes are phytase, xylanase, β-glucanase and protease. Scientists have found that the mannanase enzyme increases the production of butyrate and maintains gut health. Butyrate is short-chain fatty acid, an indispensable source of energy for cells in the gastrointestinal tract and is involved in maintaining the health of the intestinal epithelium. Thus, VEMO Corp. has developed a series of high-quality enzyme-based feed additives, ensuring for the proper feed digestion, and providing for the healthy gut microbiota:

• VemoZyme F – phytase based feed additive, for better phosphorus utilization
  
• VemoZyme 50/100 – multienzyme complex, containing xylanase, hemicellulase, β-glucanase, α-galactosidase, mannanase, amylase, protease, lipase and pectinase enzyme activities, for better feed digestion
  
• VemoZyme M – mannanase based feed additive, specifically used for degrading mannan in feed ingredients and improving the utilization rate of nutrients for animals
  
• VemoZyme P – a stable, broad spectrum protease, optimized to work efficiently in the animal’s digestive system
  

Conclusion

It is clear that probiotics, prebiotics, synbiotics and enzymes stimulate the beneficial microbiota and have a positive effect on gut health, however, with various complex mechanisms of action. Short-chain polysaccharides and oligosaccharides obtained by enzymatic degradation may also exhibit prebiotic properties. The use of digestive enzymes is often associated with increased length of the intestinal villi, leading to better absorption and utilization of nutrients. This increases the absorption surface of the intestinal tract, leading to increased feed efficiency and hence growth performance. Therefore, when considering the effects of enzymes on the digestive processes in the animal body, it is important to consider their effects on gut health.

Prof. Sabka Surdjiska