Feed transformation into biomass gain it’s a process that starts in the digestive system of the animal. As such, its health status and its functionality correlate directly with the economic results of the farmer. From mammalian research it is well known that the gastrointestinal tract is responsive and sensitive to a wide range of stressors. Some of the more common features are degeneration of the intestinal mucosa and perturbation of its barrier function and uptake mechanisms. Closely connected with the state of health of the gut is a well balanced intestinal micro-flora, which helps the digestive and absorptive process and protects the host against invading pathogens.
The host-microbe interactions are often qualitatively as well as quantitatively different for aquatic and terrestrial species. The aquatic environment is rich in microorganism (up to 105 to 106 per ml), with hosts and microorganisms sharing the same ecosystem. Thus, much more than terrestrial animals, aquatic farmed animals are surrounded by an environment that supports their pathogens independently of the host animals, as such, (opportunistic) pathogens can reach high densities around the animal. Surrounding bacteria are continuously ingested either with the feed or when the host is drinking, causing a natural interaction between the microbiota of the ambient environment and the gut environment. If the bacterial challenge exceeds a certain level, the health of the animal is in danger, as the animal alone cannot defend itself sufficiently.
During the last decade, there has been an improvement in understanding the importance of intestinal microbiota in fish. Floral health is a new concept, which underlines the importance of the microbiota to the intestinal health and performance.
As a result, there is increasing evidence that the complex microbial ecology of the intestinal tract provides both nutritional benefit and protection against pathogens, and it is vital in modulating interactions with the environment and the development of beneficial immune responses.
Several studies also have shown that different feed ingredients and changes in diet composition can affect gut structure and microbiota balance influencing digestive and absorptive functions. Alteration of the intestinal microbiota composition and consequent reduction of protective gut microflora may contribute to pathogenesis in the gut. Management of the gut flora is therefore, an important issue to achieve a good feed efficiency, animal growth and animal health. Management means selection of beneficial strains, control of their numbers, minimizing number of negative or potential pathogenic strains.
Different strategies have been used to face the problems regarding bacterial and viral threats, chemotherapy being the most used approach, using large amounts of antibiotics. Nonetheless, this should not be a routine method to be used in fish and shrimp culture due to the risks resulting from the pathogens increased resistance to antimicrobials, its cost, and environmental pollution risks derived from its use.
Nowadays, we have learned about more sustainable ways to manage gut microflora and fish performance using nutriceuticals or functional foods to modulate the health of farmed animals. There are several natural options available to manage and regulate fish gut environment which include the use of probiotics, prebiotics, immune-stimulants, phycophytic substances, and organic acids and their respective salts, commonly known as acidifiers.
Probiotics are live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance. The interaction of probiotics with the digestive tract and its endogenous microflora is a subject that is now being studied extensively and its benefits on aquatic animal health well documented and scientifically reviewed. Several studies have shown that probiotics provide protection against pathogenic microorganism present in water medium and the gut of the animals by competition with pathogenic bacteria for space and nutrients (Fig. 1), production of antimicrobial substances (lactoferrin, lysozyme, bacteriocins) and change of environmental conditions in the intestine (lowering of pH through increased production of volatile fatty acids and lactic acid).
Pre-biotics are non-digestible food ingredients (inulin, fructo-oligosaccharides) that beneficially affect the host by selectively stimulating the growth of and/or activating the metabolism of one or a limited number of beneficial bacteria in the intestinal tract, particularly bifido bacteria and lactobacilli, thus improving the host’s intestinal balance.
As an essential part of the immune system is associated with the intestine, its health is of particular importance. The gut associated immune system consists of unspecific and specific components. It provides a special category of antibodies (IgA-antibodies) which are a predominant antibody in body fluids and mucous membranes, responsible for defense reactions with pathogens. Immune-stimulants substances have been recognized as promising supplements that potentially assist in disease prevention of several organisms including fish and shrimp. These substances increase disease resistance by regulating host defense mechanisms against opportunistic pathogens which are always present in the fish surrounding environment. Immune-stimulants increase resistance to infectious disease, not by enhancing specific immune responses, but by enhancing non-specific mechanisms. Therefore, there is no memory component and the response is likely to be of short duration. The use of these immune-stimulants is an effective means of increasing the immune-competency and disease resistance of fish. Research into fish immune-stimulants is developing and many agents are currently in use in the aquaculture industry such as cell wall fragments, β-glucans, peptidoglycans, lipopolysaccharides, and nucleotides, among others.
Phycophytic substances are derived from sea algae species. They contain complex immune-stimulating carbohydrates which demonstrate immune stimulating effects activating macrophages (Fig. 2) and stimulate proliferation of lymphocytes, therefore supporting the immune system and helping fight infections.
Dietary acidification by addition of organic acids is another possible alternative to improve gut health and performance. The pH decreasing action of organic acids contributes to an improved activity of digestive enzymes and creates an impaired environment for pathogens. A combination of organic acids and their salts are commonly used to modulate the gut microflora of intensively farmed animals; this is achieved by causing a shift in the dominancy hierarchies of bacteria through the lysing of gram negative bacteria.
In conclusion, the animal’s digestive system and the animal’s health status are of utmost importance to develop performance at high level. There is increasing evidence from research that several natural feed additives can have a beneficial effect on the animals by supporting a well balanced gut microflora and improving gut health and performance.
BIOMIN has more than 20 years of experience with concepts associated with antibiotic free feeding. Continuous research work has been done resulting in very efficient feed additives. These feed additives are based on natural ingredients, which are able to unlock the performance potential of our animals. Our natural growth promoters (NGP’s) make use of a modular system combining different substances to balance the gut microflora and boost the immune-system of the targeted species.
In this symbiotic approach, all the components act together in a well-adjusted way to compete against unfavorable dietary factors including changes of feed composition, and microbial contamination of the feed and water. They allow a better utilization of the energy deriving from the nutrients of the feed and enhance the animal immune system.
Figure 1 - Competitive exclusion for space. The high population of beneficial bacteria will limit the adhesion of the pathogenic bacteria into the adhesion sites in the intestine.
Figure 2 – Macrophage activation capability of different plant extracts tested in vitro.