Natural Growth Promoters a sustainable solution to improve gut health and performance in aquaculture species
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 (Verschuere et al., 2000).
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 (Ringo & Olsen 1999). Alteration of the intestinal microbiota composition and consequent reduction of protective gut microflora may contribute to pathogenesis in the gut (Ringo & Olsen 1999). 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 numbers 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 and chemical products. 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 and phytogenic substances, and organic acids and their respective salts, commonly known as acidifiers.
Figure 1 - Competitive exclusion for space. The high population of beneficial bacteria will limit the adhesion of the pathogenic bacteria to adhesion sites of the intestine
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 (Verschuere et al., 2000, Irianto & Austin, 2002). Several studies have shown that probiotics provide protection against pathogenic microorganisms 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) (Balcazar et al., 2006).
Disease due to luminous bacteria, such as Vibrio harveyi, is one of the major problems of the shrimp industry. As a result, different technologies have been introduced to prevent the occurrence of luminous bacteria in shrimp ponds. Several studies have shown that luminous Vibrio can be eliminated from the water column and from the sediment of ponds when probiotic strains selected for their direct inhibitory effect are used (Verschuere et al., 2000). These data show that the disease problems associated with luminous Vibrio (V. harveyi) can be overcome by applying probiotic biotechnology and water ecology management. A recent study by Supamattaya et al. (2006) showed that the use of probiotics in feed is also effective in reducing the load of Vibrio bacteria in the shrimp of gut and hepatopancreas, which can reduce the risk of infection.
Table 1: Enumeration of total Vibrio spp. and Enterococcus sp. (by FISH technique) in shrimp digestive tract after feeding diets containing a single probiotic strain (Enterococcus sp.) (treatment 1) essential oils (treatment 2), or a multi-strain probiotic mixture containing Bacillus sp and Enterococcus sp. (treatment 3) for 6 weeks.
|Total Vibrio spp. (x104)||Entero coccus (x106)||Total Vibrio spp. (x106)||Entero coccus (x108)|
|Treatment 1||1.2+0.6 b||39.5+10.2 ns||32.5+28.7||9.6+6.5 ns|
|Treatment 2||34.4+12.1 a||-||86.8+35.3||-|
|Treatment 3||1.7+0.9 b||56.5+23.2||29.5+19.4||7.8+5.7|
Pre-biotics are non-digestible food ingredients (inulin, fructooligosaccharides) 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. Studies conducted by Ringo et al (2006) in Artic char have shown that inclusion of the prebiotic inulin changed the microbial community increasing the number of gram-positive bacteria like Streptococcus, Carnobacterium and Bacillus.
Phytogenics are a relatively young class of feed additives and are still rather fragmented in terms of knowledge regarding their mode of action and application strategies. They are plant derived products which are added to the feed in order to improve performance in agricultural livestock. Phytogenic feed additives (phytogenics) are an extremely heterogeneous group of feed additives originating from leaves, roots, tubers or fruits of herbs, spices or other plants. They are either available in a solid, dried or ground form or as extracts or essential oils. Within phytogenic feed additives, the content of active substances in products may vary widely, depending upon the plant part used (e.g., seeds, leaf, root, and bark), harvesting season, and geographical origin (Steiner, 2006). Phytogenics can have antioxidative and/or antimicrobial activity. Additionally some phytogenics are used to increase the palatiblity of diets, which could also lead to higher growth rates of animals (Steiner, 2006).
Essential oils are odoriferous, secondary plant products which contain most of the plant's active compounds e.g. alcohol, aldehydes, ketones, phenolic compounds, etc. Processing modifies the active substances and associated compounds within the final product (e.g. by cold expression, steam distillation, or extraction with non aqueous solvents). The plant family of Labiatae has received most interest with thyme, oregano and sage as the most popular representatives (Steiner, 2006). The antimicrobial mode of action is considered to arise mainly from the potential of hydrophobic essential oils to intrude into the bacterial cell membrane, to disintegrate membrane structures and cause ion leakage (Kroismayr, 2007). Among the herbs and spices used in animal nutrition, oregano is probably used most frequently, it's rich in carcavol and thymol, which are known to have strong antibacterial and anti oxidative properties and were described as acting synergistically (Burt, 2004).
In animal nutrition, phytogenics are an interesting category of feed additives due to their different effects. Most studies on application of essential oils in animal nutrition have been conducted in swine and poultry, however, there is increase evidence that the application of phytogenics can also be beneficial for some aquaculture species. A recent trial conducted at Biomin Aquaculture Research Center confirmed that essential oils (Biomin® P.E.P. 125) have a positive effect on pangasius fish (P. hypothalamus) growth performance (Fig. 2). When included into a commercial type feed at levels of 125 g/ton fish showed improved growth rate (6%) and improved FCR (1.32 vs 1.38).
Figure 2 - Effect of a essential oils based product (Biomin® P.E.P. 125) on growth performance of pangasius hypothalamus after 4 week trial.
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 (IgAantibodies) which are a predominant antibody in body fluids and mucous membranes, responsible for defense reactions with pathogens. Immune-stimulating 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 and shrimp. Research into fish immune-stimulants is developing and many agents are currently in use in the aquaculture industry such as cell wall fragments, ?-glucans, peptidoglycans, lipopolysaccharides, and nucleotides, among others.
Phycophytic substances are derived from sea algae species, mainly brown algae from the genera Fucus, Macrocystis, Laminaria. They contain complex immune-stimulating carbohydrates which demonstrate immune stimulating effects activating macrophages (Fig. 3) and stimulate proliferation of lymphocytes, therefore supporting the immune system and helping to fight infections.
Figure 3 – Macrophage activation capability of different plant extracts tested in vitro.
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. The mode of action of organic acids in the intestinal tract involves two different ways: on one hand they reduce the pH-level in the stomach and particularly in the small intestine, and on the other hand they inhibit growth of gram negative bacteria through the dissociation of the acids and production of anions in the bacterial cells.
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 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. These natural solutions represent a more sustainable approach than the widespread use of antibiotics, and are a preventive measure to reduce pathogenic load and manage gut health and performance in aquaculture species.
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 the 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.
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