Feed additives

Background

Feed supplements for optimum shrimp farming

The production of shrimp is growing rapidly and their diets are also becoming more sophisticated. In this article we delve deeper in to the use of phytomolecules, organic acids and prebiotics.

In shrimp farming, the reduction of antibiotic use is an important topic. The challenge is to maintain performance levels while reducing the use of antibiotics. This can be done by using phytomolecules, organic acids and prebiotics as an alternative. The combination of all supplements in the feed cleverly combines the positive characteristics of the substances and additionally uses synergistic effects. But, for optimal nutritional effects, it is necessary to adapt the method of application considering the characteristics of the supplements used.

The world’s shrimp production has grown tremendously. Over the last ten years, the compound annual growth rate has been around 10%. Photo: Dreamstime
The world’s shrimp production has grown tremendously. Over the last ten years, the compound annual growth rate has been around 10%. Photo: Dreamstime

Growth in shrimp farming

The world’s shrimp production has grown tremendously. Over the last 10 years, the compound annual growth rate has been around 10%. In 2017, 6 million tons of shrimp were produced by using about 8.5 million tons of feed. The increase in shrimp production is the result of the stagnation of wild captures since 2003.Higher quality of feeds allows higher production yields and new techniques allow higher stocking densities. The main producers of shrimp are China, Ecuador, India, Indonesia, Mexico, Thailand and Vietnam. They represent 90% of the global production with around two million hectares of production area. Smaller markets are also growing as the high potential of shrimp business arouses the interest of other countries.

Disease challenges

The main breed used in shrimp production (80%) is Litopenaeus vannamei, also known as White Leg Shrimp. It is followed by Penaeus monodon or Giant Tiger Shrimp (15%). Compared to Penaeus monodon, Litopenaeus vannamei shows better acceptance to high-density cultivation, high-health broodstock and has a lower protein requirement. One big challenge in shrimp production is the occurrence of diseases. In 2017 they caused economic losses of about US$2 billion. The most common diseases are: Early Mortality Syndrome or Acute Hepatopancreatic Necrosis Disease (EMS/AHPND), White Faeces Syndrome (WFS), White Spot Syndrome (WSS), Enterocytozoon hepatopenaei (EHP), and the Running Mortality Syndrome (RMS). High stocking densities, poor water quality and a lack of nutrients are often the best preconditions for these diseases. The resulting higher susceptibility to pathogens leads to poor health and reduced growth performance.

Use of feed supplements

Three main product groups used as supplements in shrimp production are phytomolecules, organic acids and prebiotics.

Phytomolecules

In aquaculture, the phytomolecules carvacrol and cinnamaldehyde are well-established. Both impair harmful bacteria and stop their growth by interfering with processes in the bacterial cell. They disrupt e.g. the bacterial enzyme metabolism and prevent proliferation. The extent of the inhibitory effect depends on the dosage of the phytomolecules. In order to obtain liquid feed additives for flexible use, the phytomolecules are stabilised by an emulsifier. Carvacrol and cinnamaldehyde are a good tool for the effective improvement of intestinal health and digestion.

Organic acids

Several studies with organic acids such as citric, propionic and formic acid showed that organic acids positively influence growth performance, immunity and resistance against diverse species of Vibrio.

Prebiotics

The use of prebiotics is also common practice in aquaculture. One source of prebiotics are yeast cells. The cell walls of e.g. Saccharomyces cerevisiae consist of beta-glucans and mannan-oligosaccharides. One part of the positive effect of prebiotics on intestinal health is the agglutination of pathogens. Harmful bacteria like Vibrio spp. are bound in complexes and discharged. The other part is the promoting effect on the beneficial gut flora. Only certain microbes can use mannan-oligosaccharides as energy source, e.g. lactobacilli and bifidobacteria. These beneficial bacteria help the shrimp to absorb and utilise nutrients. They also produce metabolites (organic acids) which additionally inhibit the proliferation of pathogens. All in all, mannan-oligosaccharides and beta-glucans increase intestinal balance and gut health.

Using the adequate application

It is important to know how to use the feed supplements to prevent that they are damaged or lose their efficacy. For feed millers it is important to know that phytomolecules are not heat stable. Therefore, the addition into the mixer has negative consequences. Heat treatment increases the losses of the highly volatile phytomolecules and also influences their efficacy in a negative way. In order to avoid these negative consequences, it is recommended to coat the phytomolecules onto the feed with a drum or vacuum coater after pelleting. The homogenous mixture with oil is kept in motion by a screw in the storage tank of the coater. This allows an even distribution of the additives during the coating process. The type and quantity of oil complies with the regional oil availability and the fat absorption capacity of the feed. Yeast cell walls, on the other hand, are heat stable and can be added to the raw materials of the basic feed in the mixer. On a farm, the application is similar to the coating method mentioned above. All supplements, the phytomolecules, the organic acids and the prebiotics, must be homogenously mixed with a binder (e.g. molasses, gelatin or oil) and dispensed onto the already prepared shrimp feed. This can be done on plastic tarpaulins, in basins or in pug mills. Trials showed that the feed supplements remain in and on the feed due to the fatty surface and the hydrophobic property of our emulsion. This means that the products are stable when added to the water.

Conclusion

Both, phytomolecules as well as prebiotics are effective tools in aquaculture. The combination of both brings additional benefit because of synergistic effects. In order to achieve maximum efficiency, the substances have to be applied onto the feed according to their special characteristics like heat stability.

Putting feed supplements to the test
In October 2018 a trial with a product based on phytomolecules and an organic acid (Activo® Liquid, EW Nutrition) was conducted at the Shrimp Vet Laboratory, Minh Phu Aquamekong / Nong Lam University in Vietnam. This trial evaluated the minimum inhibitory concentration (MIC) of the product against isolated field strains of Vibrio spp. Different isolated EMS/AHPND field strains from Vietnam, Thailand and Ecuador as well as different WFS field strain isolates from Vietnam were used. It showed bactericidal efficacy against specific strains of EMS/AHPND and WFS at concentrations of = 0.1 – 0.2 % of the product and growth-inhibiting activity at concentrations of = 0.1 % of the product. Another trial was done on prebiotics in shrimp feed. An agglutination test was conducted with a product based on beta-glucans / mannan-oligosaccharides (BgMOS®, EW Nutrition). The trial took place in the same institute and at the same time as the above mentioned trial. The question in this trial was, if this product agglutinates the above mentioned Vibrio spp. strains. E. coli was used as positive control. Colony forming units counted per ml (CFU/ml) served to calculate the agglutination. The study showed strong and weak agglutinations of the product with = 5 g/kg and = 0.625 g/kg, respectively, against EMS/AHPND and WFS pathogen strains.