Posted on: 2010-05-01
Microalgae trials in animal feed
The main feed market areas were microalgae may have a valuable application are summarized below:
Microalgae aquaculture feeds
The largest current application of microalgae feeds is in aquaculture. Microalgae are used fresh (e.g. live, or at least not dried) in bivalve, shrimp and fish fry and fingerling production (in the latter case via an intermediate food source, such as zooplankton or brineshrimp) (Benemann, 1992, Spolaore et al, 2006). Several companies produce aquaculture feeds using Chlorella and Spirulina, or a mixture thereof. Some examples of the use of microalgae for aquaculture:
- Microalgae species Hypneacervicornis and Cryptonemia crenulata particularly rich in protein were tested in shrimp diets (da Silva et al, 2008). Algae were collected, rinsed, dried and ground up for the feed formulations. Larvae shrimps were fed daily with one of four diets prepared with different percentages of seaweed powder: 39%, 26%, 13%, 0%. The results suggest that there is an increase in feed conversion when the levels of algae are increased. Amount of algae in fish meal resulted in significant increase in shrimp growth rates.
- A large number of marine nitrogen-fixing cyanobacteria have been tested for their nutritional value with the hybrid Tilapia fish fry; a majority were acceptable as single ingredient feeds. Very high growth rates of Tilapia fish using marine cyanobacteria with in-door and out-door cultures have been reported. The marine cyanobacterium Phormidium valderianum was shown to serve as a complete aquaculture feed source, based on the nutritional qualities and non-toxic nature with animal model experiments (Thajuddin et al., 2005).
More than 40 species of microalgae are used in aquaculture worldwide, depending on the special requirements of local seafood production.
In 1999, the production of microalgae for aquaculture reached 1000 ton (62% for molluscs, 21% for shrimps and 16% for fish) for a global world aquaculture production of 43 x 106 ton of plants and animals (Muller-Feuga, 2004).
Apart from feeding larvae and zooplankton, often with special microalgal species, the addition of Spirulina and Chlorella to common fish feed compositions seems to be a promising market. Initially, the colour-enhancing effects of phycocyanin-containing Spirulina biomass or carotenoides from Dunaliella were exploited in ornamental fish.
In recent years, questions of feed utilization and health status in the dense aquacultural fish populations became more important. Here, the addition of microalgae can, depending on concentration, directly enhance the immune system of fish, as investigations on carp have shown (Schreckenbach et al. 2001).
The addition of microalga-derived astaxanthin to feed formulations enhances the colour of the muscles of salmonids. This has a high biotechnological potential and culture techniques for Haematococcus pluvialis are well developed for this purpose (Piccardi et al. 1999); and two different types of industrial-scale closed PBR for producing astaxanthin-rich Haematococcus are in operation in Japan and Israel. In Israel, a glass tube PBR is used and in Japan, a special spherical thin layer PBR. On the Hawaiian Islands and in China, Haematococcus is cultivated in open ponds (Pulz and Gross, 2004).
Microalgae trials in poultry feeds
In poultry rations, algae up to a level of 5-10% can be used safely as partial replacement for conventional proteins (Spolaore et al, 2006). The yellow colour of broiler skin and shanks as well as of egg yolk is the most important characteristics that can be influenced by feeding algae (Becker, 2004). Moreover, the Institut für Getreideverarbeitung (Bergholz-Rehbrücke, Germany) produces a natural feed with the algae Chlorella and Arthrospira called Algrow.
Ginzberg et al. (2000) studied role of algae, Porphyridium sp. as feed supplement on metabolism of chicken. Earlier results in the same laboratory showed a reduction in serum cholesterol and triglyceride levels in rodents fed with red algal biomass. In this study lyophilized algae biomass was fed to chickens at a proportion of 5% or 10% of the standard chicken diet. Chickens fed with algae biomass consumed 10% less food and their serum cholesterol levels were significantly lower (by 11% and 28% for the groups fed with 5% and 10% supplement, respectively) as compared with the respective values of the control group (with unsupplemented diet). Egg yolk of chickens fed with algae tended to have reduced cholesterol levels (by 10%) and increased linoleic acid and arachidonic acid levels (by 29% and 24%, respectively). In addition the colour of egg yolk became darker, indicating that higher carotenoid was produced (2.4 fold higher).
Other poultry feeding studies with Spirulina (up to 30%) showed that both protein and energy efficiency of this alga were similar to other conventional protein carriers up to a level of 10% (Becker, 2004). Significantly higher growth rates and lower non-specific mortality rate were observed in turkey poults fed with Spirulina at the level of 1-10 g.kg -1 diet.
Waldenstedt et al. (2003) analyzed the effects of a dietary astaxanthin from the microalgae Haematococcus pluvialis on broiler chickens performance. The results indicated that tissue astanxanthin and carotenoid concentrations increased with increasing levels of algal meal inclusion. The results also indicate that algal meal could reduce caecal colonization of Clostridium perfringes.
Microalgae trials in swine feeds
Abril et al. (2003) studied the potential toxicity of DHA-rich microalgae (DRM) from Schizochytrium sp. administered in the diet of growing swine. The only DHA-rich microalgae treatment related changes were higher weight gain and feed conversion efficiency. The administration of DRM (at up to five times the anticipated commercial dose) did not produce any treatment related adverse effects in commercial strains of swine.
Microalgae trials in pet feeds
Another very promising application for microalgal biomass is the pet food market, where not only the health-promoting effects but also effects on the external appearance of the pet (shiny hair, beautiful feathers) are of consumer importance. Studies on minks and rabbits provide evidence of such effects for pets (Pulz and Gross, 2004).
Other microalgae trials
Belay et al. (1996) reviewed potential of Arthrospira (Spirulina) in animal feed. About 30% of the current world production of 2000 tõn Spirulina is sold for animal feed applications. Some of these positive effects of Spirulina like increased growth rate, colour enhancement and general tissue quality may be nutritional effects. However, the fact that growth rates are improved even at 0.1% Spirulina supplementation may suggest the presence of substances that may mimic the effects of or stimulate production of growth hormones. The most promising application may be its immune enhancement effects and through this its antiviral and anti-bacterial properties, since these effects are exhibited at very low supplemental concentrations in the feeds. Spirulina or its extracts may accelerate development of the immune system of many animals especially during the early stages of their lives. Presently Arthrospira is widely used as food additive and can replace 50% of protein diets in existing feeds.
Astaxanthin from H. pluvialis is therefore of interest comparing with other sources. More than 80% of astanxanthin from this microalgae, is found in an esterified form, whereas in synthetic astaxanthin it is in the free form. In birds, astaxanthin in an esterified form has been shown to be more efficiently absorbed than free astaxanthin (Latcscha, 1990).
In mice infected with Helicobacter pylori, treatment with H. pluvialis algal meal significantly reduced the bacterial load of H. pylori in the stomach (Wang et al., 2000). This was explained by the effects of astanxanthin on cytokines produced by H. pylori specific T- cells (Bennedsen et al., 1999).
Fact 1 ________________________________________________________________
The use of microalgae for animal feed started in the early 70s.
Microalgae incorporation in feeds
Microalgae may be incorporated in feeds at different percentages, depending on the final feed product. The several final products and the respective medium percentages of microalgae incorporation are described in the following chart:
Although microalgae are able to enhance the nutritional content of conventional food preparations and hence, to positively affect the health of humans and animals, prior to commercialization, algal material must be analyzed for the presence of toxic compounds to prove their harmlessness. The next step is to get approval for their incorporation as dietary supplements or additives (see section Animal nutrient requirements - Regulations ).
Some constituents of microalgal biomass may represent constrains on its incorporation on feeds, like nucleic acids, toxins and heavy-metal components. Other issues that might constrain microalgae incorporation as dietary supplements are their digestibility, and the high amount of salt in marine microalgal species.
One of the very few constituents present in all living organisms and hence in algae, and which under certain circumstances may be counted as toxin, are nucleic acids (RNA and DNA). Since these constituents are the source of purines, they represent a limitation in the use of alga and other forms of SCP (Single Cell Protein) as food or feed ingredient as the Protein Advisory Group has recommended that the daily intake of nucleic acids from all sources should not exceed 4.0 g per day, and from unconventional sources (as microalgae) should not excedd 2.0 g per day (Becker, 2004).
Cyanobacteria are the predominant toxic algal strains. These strains occur in blooms on rivers and lakes all over the world. No such cases have been reported in connection to mass-cultured algae, as the culture conditions are strictly controlled. The several trials performed so far on mass-cultured algae, for both chemical analysis of algae biomass and feeding trials had return negative results for algae toxicity (Becker, 2004).
One of the major problems associated with algae large scale production is the elevated amounts of various heavy metals (lead, cadmium, arsenic, etc). At present no official standards exist for the heavy metals content of microalgal products but, on a voluntary basis, some algae manufacturers have established internal guidelines for metal levels in their products (Becker, 2004).
Regarding microalgae digestibility, the cellulosic cell wall of most algae strains poses problems in digesting their biomass, since it is not digested by non-ruminant animals (chickens, turkeys, pigs, pets, horses, etc). From the tests performed as yet, the overall digestibility of algae carbohydrates is good and there seems to be no limitation in using dried microalgae as a hole, but this has to be evaluated for each algae identified as a potential feed material (Becker, 2004). If a certain algal strain has low digestibility levels, the biomass may anyway be incorporated as feed material, but needs effective treatment to disrupt the cell wall, making the algal constituents accessible for digestive enzymes. The processes employed may be physical (ex. boiling), high temperature drying and to a certain extent even sun drying, and chemical methods (ex. autolysis) (Becker, 2004).
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