It is no secret that optimum animal performance encompasses a number of factors, including genetic characteristics of the specie, quality of the diets, environmental condition and absence of disease outbreaks. Add to this industry pressure, such as the need for efficient use of increasingly expensive raw materials or health management, and the picture becomes more complex. A focus on good gut health can help to successfully navigate this large set of considerations and set the foundation for better growth.
Defining gut health
The gut is a key organ system which mediates nutrient uptake and use by the animals but also plays an important role in providing an effective barrier against environmental pathogens. Hence, a well-functioning and healthy gut is the cornerstone of performance in aquatic animals. At BIOMIN we define gut performance management according to three objectives: to improve the efficiency of the gut; to prevent gastrointestinal disorders and related side effects; and to re-establish gut integrity after a dysfunction.
Identifying the right solution
The aquaculture industry is characterized by a large variety of species compared to other methods of livestock production. In addition, there is diversity in feeding regimes (carnivorous, omnivorous or herbivorous), rearing environments (marine, brackish, or freshwater habitats) and temperature (cold, sub-tropical or tropical climates) and feed formulations. Identifying the correct tool to promote good gut health and growth enhancement must take into consideration these elements along with the value of the species and the specific challenge affecting the production.
Consequently, we work continuously with different aquaculture species, identifying the most promising compounds and strategy to achieve the best growth performance for each. Here we provide several examples of ways to support gut health and growth enhancement using distinctly different tools.
The high cost of fish meal
The reliance on less costly protein sources and low-nutrient dense diets to replace costly fishmeal —whether for economic or sustainable reasons— will most likely lead to lower protein digestibility, higher amino acid imbalance, higher carbohydrate and fiber content, since plant raw materials are less digestible and negatively impact the gastrointestinal tract. The presence of undigested nitrogenous compounds in the intestine favors the formation of ammonia and biogenic amines by the intestinal microbiota. These toxic compounds cause an imbalance of the intestinal microbiota, resulting in inflammatory processes and accelerated turnover of the intestinal tissue, leading to poor performance. In addition, sub-optimal animal performance due to inefficient nutrient use, results in increased feed usage and consequently higher production costs, environmental problems (higher ammonia emissions) and disease vulnerability.
Phytogenic feed additives —consisting of herbs, spices, extracts or other plant-derived compounds— have gained considerable attention as a tool to achieve growth performance. The active ingredients (e.g. phenols and flavonoids) can exert multiple effects in animals, including improvement of feed conversion ratio (FCR), digestibility, growth rate, reduction of nitrogen excretion and improvement of the gut flora and health status. In the case of nutrient sparing or fish meal replacement, phytogenics can stimulate the digestive secretions, increase villi length and density and increase mucous production through an increase in the number of globlet cells. As a result, phytogenics can improve feed digestibility, especially for proteins and amino acids.
In a trial with gilthead sea bream (Sparus aurata) at the University of Algarve in Portugal, fish were fed a low fishmeal diet (14%), supplemented with a matrix-encapsulated phytogenic feed additive (Digestarom® P.E.P. MGE). Dietary supplementation with Digestarom® P.E.P. MGE showed the best results with a significant reduction of FCR from 1.28 up to 1.12 and an improvement of specific growth rates (from 1.76 to 1.82 %.day-1) (Figure 1). Inclusion of the phytogenic products in the diet significantly enhanced (p<0.05) protein and fat retention (Figure 2). The results also showed that a significant reduction of total nitrogenous losses, which was clearly associated with lower metabolic losses (Figure 3).
Figure 1. Feed conversion ratio and specific growth rate of sea bream as affected by diet supplementation with Digestarom® P.E.P. MGE.
Source: BIOMIN trials, 2012
Figure 2. Nutrient retention of sea bream as affected by supplementation with Digestarom®
Source: BIOMIN trials, 2012
Figure 3. Nitrogen budget (gain, fecal losses and metabolic losses) in sea bream with supplementation by Digestarom®
Source: BIOMIN trials, 2012
Probiotics for pathogen control
The use of beneficial bacteria (probiotics) to control pathogens is gaining acceptance in aquaculture, given the richness of microbial life in aquatic environments. Probiotic bacteria can maintain a healthy balance of bacteria in the gut through: competitive exclusion (beneficial bacteria exclude potential pathogenic bacteria through competition for attachment site and nutrients); antagonism (inhibit the growth of pathogenic bacteria by producing, for example, bacitracin and polymyxin (produced by Bacillus sp.). Probiotics can also promote gut maturation and integrity, modulate and stimulate the immune system, prevent inflammation, boost the metabolism, increase digestive enzyme activity, decrease bacterial enzyme activity and ammonia production, improve feed intake and digestion, and neutralize enterotoxins. Following the previous knowledge a total of 60 juvenile trout’s (Oncorhynchus mykiss) were used in a trial carried out at a commercial trout farm in Karditsa, Thessaly, Greece. Here we tested the effect of dietary incorporation of AquaStar® Hatchery (multi-strain probiotic) on growth performance and intestinal bacteria count. Here we saw that probiotic, significantly (p < 0.05) increased body weight gain in the test group compared to the control by an average of 10.8 % feed conversion ratio was significantly (p < 0.05) improved by 18.8 % (Figure 4) and Lactobacilli loads were 54.6 % higher in probiotic fed fish compared to fish fed the basal diet only (Figure 5). The lactic acid production makes the microbial environment acidic, which inhibits the growth of some harmful bacteria.
Figure 4. Feed conversion ratio of trout with diet supplementation using AquaStar® Hatchery
Source: BIOMIN trials, 2010
Figure 5. Lactobacilli count in trout gut fed AquaStar® Hatchery supplemented diets.
Source: BIOMIN trials, 2010
Boosting beneficial bacteria
Prebiotics are non-digestible feed ingredients that beneficially affect the host by selectively altering the composition and metabolism of the gut microbiota. Prebiotics can also provide energy for the growth of endogenous favorable bacteria in the gut, thus improving the host microbial balance. Prebiotics have been reported to enhance host defense and reduce mortality of fish caused by the invasion of gut pathogens. They can also, by enhancing the immune response of aquatic organism, increase the clearance of pathogens from the gut. With regard to the immune-enhancing effect of prebiotics, this may in part be due to direct interaction between prebiotics and gut immune cells receptors as well as due to an indirect action of prebiotics via preferential colonization of beneficial microbes and microbial products that interact with immune cells.
At Aquaculture Center for Applied Nutrition (ACAN) in Thailand we used 117g red tilapia (O. mossambicus X O. niloticus) to test the effect of Levabon® Aquagrow E, spray-dried autolyzed yeast (Saccharomyces cerevisiae) product, on growth performance. The results obtained showed that Levabon® Aquagrow E improved specific growth rate (SGR) by 5% and the feed conversion rate (FCR) decreased by 4% (Figure 6) by addition of 0.4 % Levabon® Aquagrow E to the diet.
Figure 6. Specific growth rate and feed conversion rate of red tilapia fed Levabon® Aquagrow E.
Source: BIOMIN, 2010
A sustainable replacement for AGPs
Unlike antibiotic growth promoters, which kill both beneficial and harmful bacteria, organic acids attack Gram-negative (pathogenic) bacteria while leaving the beneficial ones in place. In the undissociated form, organic acids can freely diffuse through the semi-permeable membrane of the bacteria into the cell cytoplasm. Once in the cell, where the pH is maintained near 7, the acid will dissociate and suppress bacterial cell enzymes (e.g., decarboxylases and catalases) and nutrient transport systems. The reduction of pathogenic intestinal bacteria, which can produce toxin causing damage of intestinal villi and crypt structure, is directly associated with the improved gut structure.
In a trial at ACAN, Pangasius catfish fed the Biotronic® supplemented diet had an improvement of 1.72% in SGR compared to the control group and 0.86% when compared with the flavomycin group (Figure 7). Analyzing the bacteria counts in the gut, was possible to observe that animals fed Biotronic® supplemented diets had a considerable reduction in total bacteria count, -76% than the control group and -43% when compared with the flavomycin group (Figure 8).
Figure 7. Specific growth rate Pangasius catfish (Pangasionodon hypophtalmus) fed Biotronic® supplemented diet or flavomycin, compared to control group.
Source: BIOMIN, 2014
Figure 8. Total bacteria count in pangasius catfish gut (Pangasionodon hypophtalmus) fed Biotronic® supplemented diet or flavomycin, compared to control group.
Source: BIOMIN, 2014
Understanding gut health requires the elucidation of the complex interactions between all different components that will allow the gut to perform under normal physiological functions and to maintain homeostasis, thereby supporting its ability to withstand infections and non-infectious stressors. Given the wide range of considerations in aquaculture production, a focus on good gut health can help farmers to enhance growth. A number of novel feed additives –such as probiotics, prebiotics, phytogenics and organic acids– can help support gut health and growth enhancement.
This article originally appeared in Aquaculture Scoop June 2015 issue.