In this article, we present a wide range of strategies that embrace ingredients, additives, and other nutritional strategies that may be of interest for the management of gut health. To facilitate the understanding of the mechanism of action and the expected effects of each strategy, we have framed them in four major mechanisms of action that will be presented in detail in the next articles: enhance the immune response, reduce the burden of pathogenic bacteria, stimulate the colonization of a beneficial microbiota and stimulate digestion (Table 1). It is important to mention that some of these strategies owe their results to multifactorial effects, therefore, they can be included in different mechanisms.
Table 1. Classification of the main modes of action present in different strategies to improve intestinal health.
|Potentiation of immune response and barrier function||Reduction of pathogenic bacteria||Stimulation of beneficial microbiota||Stimulation of digestion and utilization of nutrients|
|Polyunsaturated fatty acids||Fermentable fiber||Fermentable fiber||Fermentable fiber|
|Probiotics||Protein reduction||Protein reduction||Protein reduction|
|Prebiotics||Fermented diets||Fermented diets||Fermented diets|
|Symbiotics||Diets with low buffer capacity||Probiotics||Diets with low buffer capacity|
|Nucleotides||Probiotics||Prebiotics||Reduction of anti-nutritional factors|
|Bioactive proteins and peptides||Prebiotics||Symbiotics||Probiotics|
|Amino acids||Symbiotics||Inorganic and organic acids||Symbiotics|
|Phytogenic||Inorganic and organic acids||Enzymes||Inorganic and organic acids|
|Trace elements||Bioactive proteins and peptides||Enzymes|
|Trace elements||Bioactive proteins and peptides|
Probiotics: Live microorganisms that can transfer benefits to the host when they are ingested in a suitable form and quantity. Currently, the most popular probiotics in swine production belong to the genera Bacillus, Lactobacillus, Bifidobacterium, Enterococcus and Saccharomyces. They have been reported the ability to enhance the immune response, reduce the burden of pathogenic bacteria, stimulate colonization by a beneficial microbiota and stimulate digestion.
Prebiotics: Non-digestible ingredients that benefit the host by selectively stimulating the growth or activity of a bacteria (or a limited number of bacteria) in the intestine. The most commonly used prebiotics in pigs are mannan-oligosaccharides (MOS), fructose-oligosaccharides (FOS), inulin or lignocellulose.
Symbiotic: A specific mixture of probiotics and prebiotics, where the prebiotic improves the survival, implantation or function of the probiotic microorganisms. It is a concept that it is still not significantly implemented in pigs, mainly because its effects and synergies can be greatly affected by external conditions. However, they are expected to become more popular in the future thanks to the greater understanding that molecular analysis techniques provide us. Some combinations used in pigs have been FOS and Lactobacillus paracasei (Bomba et al., 2002) or inulin with Enterococcus faecium (Bohmer et al., 2005).
Organic acids (and their salts): Highly energetic products that are used in animal feed due to their high digestibility, acidifying capacity, stimulation of digestive function, antimicrobial power and stimulation of a beneficial microbiota. The most commonly used acids as feed preservatives are formic and propionic. Conversely, acetic, butyric, citric, lactic and fumaric acids are frequently used in young animal diets to avoid the appearance of post-weaning diarrhea, improving digestion and reducing the presence of pathogens.
Enzymes: Exogenous enzymes that are incorporated into the diet due to their potential to improve the use of nutrients in the diet as well as to influence the microbiota profile of the intestine. The most commonly used are phytases, xylanases, β-glucanases or proteases.
Nucleotides: They are the structural unit of the nucleic acids of the cells, purine and pyrimidine bases, which are components of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Under normal conditions, they are synthesized by the animal on the basis of precursors (amino acids), or by means of the degradation of amino acids and nucleotides of the diet. However, when there is a rapid growth, disease, limited consumption of nutrients or endogenous disorder, it is considered that the ingestion of exogenous nucleotides can bring benefits. They have been attributed to having the capacity to modulate the immune response and improve the utilization of nutrients.
Bioactive proteins and peptides: These are proteins or components of proteins capable of exerting a marked antimicrobial activity or other specific biological activities. They stand out for their potential in intestinal health:
- Glycomacropeptide: Peptide obtained from the digestion of whey with K-casein. It has been attributed immunomodulatory functions, protection of the intestinal barrier and antimicrobial capacity.
- Lactoferrin: Glycoprotein present in milk with a high capacity to bind iron. It can exert antimicrobial and immunomodulatory activities.
- Ovotransferrin: Glycoprotein present in the egg white (albumen) with analogous effects to lactoferrin in mammals. It can exert antimicrobial and immunomodulatory activities.
- Growth factors: Peptides present in body fluids (mainly milk) with the ability to stimulate cellular mitosis, regenerative capacities of intestinal morphology and immunomodulation.
- Immunoglobulins: Proteins from milk, animal plasma or chicken eggs. They are bioactive substances that provide passive immunity to the animal and are able to prevent the adherence of pathogenic bacteria to the epithelial cells, to agglutinate bacteria, to neutralize toxins and to inactivate viruses.
- Lysozyme: Protein extracted mainly from the egg or milk, with antimicrobial activity against Gram-positive bacteria (for causing lysis of the cell wall) and with immunomodulatory properties.
Amino Acids: The use of crystalline amino acids enables to reduce the levels of crude protein in the diet (a nutritional strategy to improve intestinal health), covering more accurately the "ideal" protein profile. On the other hand, the amino acids threonine, glutamine, arginine and serine have a prominent role in intestinal health due to their ability to influence intestinal metabolism and architecture.
Phytogenics: They include aromatic plants (herbs and species), plant extracts and volatile acids (usually known as "essential oils"). The main active principles are volatile acids (thymol, cinnamaldehyde, β-ioninea and carvacrol) and polyphenolic compounds. They have attributed the ability to modulate the immune response and intestinal microbiota (with antimicrobial effects against pathogenic bacteria).
Trace elements or rare elements: They are required in minimum quantities to support the growth, development and optimal function of an organism. The most important in relation to intestinal health is zinc, and to a lesser extent copper, which are necessary for many metabolic processes. A high inclusion of zinc oxide (ZnO) (from 2000 to 3500mg / kg) can improve intestinal health by reducing pathogens, improving digestion, barrier function and the animal's immune system. However, due to the environmental problems associated with conventional ZnO, it is falling into disuse. Currently, new improved forms are being introduced with more therapeutic efficacy at lower doses such as microencapsulated ZnO.
Fermentable fiber: The increase in fermentable fiber provides a substrate for the fermentation of colonic bacteria, with benefits that include a more complex bacterial population, more production of short-chain fatty acids in-situ and modifications in the digestive tract and mucosal integrity.
Polyunsaturated fats: Its supplementation, in particular with the omega-3 essential fatty acid (for example, with fish oils or flaxseed) can provide benefits at the immune level by being structural components of cell membranes, signaling molecules and synthesis precursors of eicosanoids (inflammation promoters).
Protein sources of high biological value and high digestibility: highly digestible and palatable protein sources are widely used in early-age diets, not only for their high nutritional value but also for their properties of influencing intestinal health.
- Hydrolyzed intestinal mucosa: It has very high palatability and presence of bioactive peptides with antimicrobial and immunomodulatory effects.
- Spray porcine plasma: Includes immunoglobulins and peptides that transfer passive immunity to the animal.
- Egg yolk (immunized): From chickens that have been immunized against specific pathogens. In addition to a high content of quality protein, they include antibodies with the ability to neutralize specific pathogens.
- Bovine Colostrum: It contains high levels of antimicrobial peptides, immunoglobulins and growth factors that help to modulate immunity as well as to confer passive immunity against pathogens.
- Whey: It has a high content of cysteine that provides immunomodulatory effects and contributes to the synthesis of glutathione, a potent intracellular antioxidant.
Adjust protein levels: The reduction of protein levels in the diet reduces the bacteria capable of fermenting it, limiting the presence of pathogens and inflammation of the intestinal mucosa. However, in order to reduce protein levels to levels of <180g/kg, it is necessary to supplement the ration with synthetic essential amino acids.
Pre-fermented diets: pre-fermented liquid diets are of special interest. Fermentation by lactic acid bacteria improves the availability of nutrients and has also been reported to modulate the immune response and intestinal microbiota.
Diets with low buffer capacity: Diets with low capacity to block gastric acid, especially associated with mineral ingredients and protein concentrates. They are especially useful in young animals with a limited acidification capacity and can provide benefits such as pathogen reduction and improvement of the digestive capacity.
Decrease the presence of anti-nutritive factors: Substances present in vegetables that reduce feed intake, decrease digestibility and/or increase the viscosity of the food. There are processed vegetable concentrates currently available in the market, which are more nutritious and with lower levels of anti-nutritive factors. For instance, soy protein hydrolyzed concentrates.