||Li Biao technical manager Angel Yeast, China
As a major component of yeast, yeast cell wall has various effects, like improving nonspecific immunity, increasing resistance to infection, adsorbing mycotoxins and regulating the micro-environment of an animal’s digestive tract. In recent years, the use of commercial yeast cell wall has received more attention and has become accepted widely, which is attributed to advantages of naturality, non-residual and no drug resistance.
By Li Biao, technical manager, Angel Yeast, Yichang, Hubei, China
Yeast cell wall is composed of complex polymers of β-(1,3)/(1,6) glucan, mannan-oligosaccharide (MOS) and chitin. As shown in Figure 1, MOS is located on the surface of the cell wall. Yeast glucans are major cell wall components often present as the inner wall layer and associated with other cell wall components such as chitin. β-(1,3)/(1,6) glucan is known to exert remarkable benefits on the immunity of animals. MOS is able to play important roles in binding mycotoxins and improving the micro-environment of the animal digestive tract.
Mode of action
Yeast cell wall has an ability to stimulate immunity activity, depending largely upon the primary structure, helical conformation, branch, molecular size, as well as nature of substituent group, etc. β-glucan, as an immune modulator substance, is able to stimulate non-specific and specific immunological response, activate T cells, B cells, macrophages and natural killer (NK) cells, boost resistance to disease, and thus improve the production performance of animals.
The role of MOS relies chiefly upon the chemical construction. The main chain of yeast MOS consist of 1,6 bond, connection of 1-4 mannose and α-1,3 bond composes the branch. The end of mannose molecular connects by β-1,4 bond N-acetyl ketone disaccharide, the latter links to asparagine in protein polypeptide chain, forming the net structure of mannoprotein. Monogastric animals digest carbohydrates principally confined to β-1,4 glycosidic bond, which results that MOS enters directly into the back of the small intestine rather than is digested and adsorbed by the animal. Recently, various research has demonstrated that MOS was capable of either adsorbing mycotoxins by physical action or reducing the absorption and distribution of mycotoxins directly; nevertheless, it could not have any negative influence upon other nutrients in feed.
The addition of yeast cell wall in feed has the capacity to improve liver function and increase antibody titer of pigs after injection of vaccine. Piglets of the control group drenched normal saline from birth to 28 days old, piglets in treatment 1 to 3 were fed with different levels (0.1 g, 0.2 g, 0.3 g) of yeast cell wall instead of normal saline respectively; from weaning to 42 days, the control group fed with basal diet, piglets of group 1 and 3 fed the same diet supplemented with 500 g/t, 1,000 g/t, 2,000 g/t of yeast cell wall separately, which was conducted by yeast technology research and promotion centre in China. Liver function and antibody titre in the piglets are presented in Figures 2 and 3; the results suggested that liver function and the antibody level of piglets fed with yeast cell wall were improved noticeably.
The application practice indicated that, long-term addition of yeast cell wall in feed, could contribute to the decontamination of pathogens in pig farms. Statistic analysis was led by Wu and others (2008) of the positive appearance of Porcine Circovirus (PCV2) on several large-scale pig farms selling 10,000 pigs per year in eastern China post and pre supplementation of yeast cell wall. All farms tested PCV2 antibody titre before using yeast cell wall, and then tested again after utilising yeast cell wall for half a year or longer, the result is shown in Table 1.
As an immunopotentiator supplemented in pig feed, the effective dosage of extracted β-(1,3)/(1,6)-glucan can drop strikingly, it is therefore necessary to choose the appropriate dose. In the study of Wang and others (2007), to evaluate the effects of dietary supplementation with β-(1,3)/(1,6)-glucan extracted from Saccharomyces cerevisiae on cellular and humoral immunity of weanling pigs, the study was conducted with 28 day weanling piglets reared in a common environment during an experimental period of four weeks. The results in Table 2, indicate that a low supplementation dose of β-(1,3)/(1,6)-glucan is beneficial for resistance to viral infections, but high dose supplementation might lead to immune maladjustment. Consequently, the dosage of yeast cell wall as a feed additive, needs to be controlled.
Effect on production performance
The appropriate yeast cell wall is able to improve non-specific immunity and adsorb multiple mycotoxins. Dietary supplementation with yeast cell wall has a positive influence on growth performance. In 2006, Duan and others studied the effect of yeast cell wall on growth performance and diarrhoea in weanling pigs (Table 3). As shown, the addition of 0.05% yeast cell to the feed may help to reduce diarrhoea considerably and average daily gain (ADG) was increased by 7.6% in comparison to the control group.
Besides the good nutritional value, yeast cell wall can also be applied as an adsorbent for mycotoxins. As a mycotoxin binder, yeast cell wall has numerous characteristics as follows: Binding mycotoxins, especially zearalenone (ZEN); unaffected by the pH of the gastrointestinal tract; without changing nutritional value (regarding mineral and vitamin) in feed; no residue in animal and no negative effect on human health.
The adsorption rate with regard to major mycotoxins was analysed by the yeast technology research and promotion centre in China. The results, as shown in Table 4, indicated that yeast cell wall has a certain ability to bind aflatoxin (AFT), zearalenone (ZEN) and deoxynivalenol (DON).
In conclusion, using yeast cell wall offers considerable prospects in rendering beneficial action on pig health, accelerating non-specific immunity, reducing mycotoxin toxicities in feed and improving production performance.