The trick therefore is to stimulate the animal’s own innate immune system at quite a low-level without triggering a full blown immune response. Farmers realise that full-blown immune responses are to be avoided because they cost the animal a lot in terms of the energy that they divert from growth and weight gain.
The innate response should always be the first line of defence against pathogens because it can be activated immediately and can act very quickly on the pathogen. It will be the same whenever the body encounters that pathogen. The mechanism of this type of immunity consists of recognising the unique molecular patterns shared by numerous pathogens. The innate immune system controls the expression of molecules that fight against infectious agents.
The elements associated with the innate immune response can act on the pathogen directly or indirectly, by producing effector cells (cytokines etc). These subsequently trigger the adaptive immunity by activating the animal’s own T and B cells ― small lymphocytes that actively seek out and kill pathogens.
A whole range of specific cells and molecules steer the innate immune response, ranging from substances such as mucosal agglutinins; lectins; pentraxins; lysozyme; complement proteins; antibacterial peptides and immunoglobulins.
In recently years, sulfated polysaccharides have generated huge interest particularly to immune mechanisms of the innate immune system. Algal polysaccharides are complex carbohydrates thatdo not occur in terrestrial plants. They are supposed to influence the immune system by a vast number inadequately understood pathways.
Polysaccharides contain repetitive structural features which are chains of monosaccharide residues joined together by glycosidic bonds. Fucoidan ― a sulphated polysaccharide found in the cell walls of brown algae ― is one such molecule that has been effective as as an immunostimulant in many different animals from livestock to shrimp.
These products have been shown to be successful against pathogens like viral and bacterial diseases. In shrimp for example, experimental administration of fucoidan mixed in the diet has resulted in a 93% increase in survival compared to controls.
Another example is Ulvan ― a water-soluble polysaccharide found in certain green seaweeds. In addition, these polysaccharides can also act as strong pre-biotics, capable of modulating the microflora towards a favorable composition and favoring the development of beneficial bacteria and inhibiting potentially pathogenic micro-organisms. The latter strategies have the advantage of being easily applicable to large feed volumes at the feed mill and thus avoiding having to make major and costly adaptions to production protocols at farm level.
Feed solution application
Regular intake of sulphated polysaccharides from marine algae for a general stimulation of the animal’s state of defence enables it to strengthen its defence system. Repeated use stimulates the ‘basic’ immune system and boosts the defence condition of the innate system. The use of polysaccharides upstream or downstream of a prophylactic programme may be an asset in enhancing the level of immune protection of farmed animals and in contributing to a better control of the infectious pressure on mono cultures such as salmon farming.