Yeast cells and β-glucans – Multibiotic factors for successful animal nutrition

Photo 1: Cell wall of brewers' yeast (Saccharomyces cerevisiae; magnitude: x5,0000

Yeast cells can be used in many different ways in animal production. Not only the entire yeast cells can be fed, but so can the cell walls or even extracts of cell walls. This article dives into the effects of all different options for use in pigs.

By Dr Jan Frericks, Leiber, Germany

Stomach ache as a result of stressful situations is not uncommon in farm animals, especially those used for breeding. A sure indication of this kind of stress is a reduced intake of feed and diarrhoea. Metabolism has an intermediate response involving a diminished intestinal mucosa barrier function, a compromised immune status and an increased demand for specific nutrients and active ingredients.
Due to its multibiotic effect, gently-dried brewers’ yeast can work to restore balance in each case: When malt extract is fermented during the brewing process, cells of the yeast species Saccharomyces cerevisiae accumulate within them high concentrations of minerals and trace elements, amino acids, vitamin B and enzymes, as well as many micro-nutrients. Brewers’ yeast also contains nucleosides and nucleotides, building blocks of the somatic and immune system cells. This high concentration of active ingredients and the fact that they are in an organically-bound form, as well as the easy availability of the ribonucleotides, promotes cell regeneration in the mother. At the same time, piglets, for example, are assisted from the outset with the cell growth required for the development of the intestinal mucosa and immune system.
Moreover, only cells of the yeast ­species Saccharomyces cerevisiae are endowed with a cell wall composed of specific glycosidically-bonded mannans and β-glucans. This is characterised by a complex network structure with a very large surface area and strong adsorption affinity.
Recent studies by Zentek in 2012 have shown that native brewers’ yeast is capable of protecting the intestinal mucosa of piglets from attack by infectious agents such as Salmonella species. In this experiment, epithelial cells were taken from the jejunum of pigs and Salmonella species were added in vitro as a function of time. It showed a significant (p < 0.05) dose-dependent inhibition of Salmonella typhimurium. These results too demonstrate the prebiotic nature of cells of the yeast species Saccharomyces cerevisiae: An increase in the supply of substrate increased the significance (P < 0.01), see also Table 1.

MOS – prebiotic yeast cell walls
Yeast cell walls contain specific mannan-oligosaccharides (MOS). More specifically, these building blocks of the cell walls are called β-glucans and mannans. The latter serves as a growing medium for the beneficial flora found in the gut. These prebiotic properties are thus indirectly responsible for the suppression of pathogens. Ultimately, yeast mannans help in establishing a balanced microflora in the intestine (eubiosis). Moreover, mannan-­oligosaccharides are able to bind infectious agents and their toxins as well as mycotoxins. The simultaneous enhancing of the intestinal mucosa’s barrier function inhibits these toxins from entering the systemic circulatory system and the metabolic damage and performance degradation that would ensue.
Photo 1 shows yeast cell walls (Biolex-MB40, Leiber), that typically contain around 20-25% mannans and 25-30% β-glucans. This is about three times the concentration found in natural yeast. Processing techniques further enhance the availability and effectiveness of these constituents. For this reason, the benefits arising from their use as a constituent of compound feed can be realised with a dose as low as 0.2%-0.5%, even in situations where the feed has elevated levels of mycotoxin contamination or where infection pressure is high. Lower concentrations or mixtures involving other glycosidically-linked carbohydrate fractions are ­indicators of inferior quality.

β-glucans
β-1,3/1,6-(D)-glucan molecules can be isolated from the cell wall using special hydrolytic processes. They consist of a characteristic β-1,3 glucose backbone connected to a β-1,6 glucose backbone. Only this free β-glucan structure from Saccharomyces cerevisiae has an immunomodulatory effect on the metabolism and is, in contrast to intact yeast cells or mannan-oligosaccharides, able to pass through the epithelial barrier in the intestine with the help of specialised M cells. β-glucans act in such a way that they are able to identify pathogens, bind to them and present the pathogens’ particular vulnerability to the immune system. Under stress conditions, a high-yield sow is thus able to ‘handle’ germs and toxins much more effectively. The main difference between β-glucans and an actual infection is that β-glucans do not possess any pathogenic properties and thus act without causing any adverse health effects.
Recent studies at Anhalt University in Germany confirm elevated immunoglobulin concentrations in the blood serum of sows and piglets when β­-glucans from brewers’ yeast (Leiber Beta-S) was included in their feed.
From the 70th day of gestation, 36 sows were administered 0.05% β-glucans from brewers’ yeast in the ­gestation feed and subsequently in the lactation feed. The control feed contained no β-glucan and the piglet feed did not contain any β-glucan either. Blood samples were taken from the sows and piglets on the fifth and 28th days following farrowing.
The results show a significant increase (p < 0.05) in immunoglobulins (IgG) in the blood serum of sows on the fifth day of lactation. This effect diminishes towards the end of lactation. Concurrent to this, the lysozyme concentration was significantly elevated during the entire lactation period. Lysozyme is a component of the non-specific immune system that renders infectious agents harmless by lysing their cell membranes.
A significant finding of this experiment was the fact that the non-specific immunocompetence of the mothers was passed on to the piglets. The immunoglobulins IgG in the serum of the piglets were also significantly altered (Figure 1). The positive effect of β-glucans is confirmed by the animals’ performance parameters: The birth weight of piglets in the experimental group was significantly higher and the relative piglet losses reduced by more than 17%. The weight gain and the number of piglets reared are both evidence for the increased vitality of the animals (Figure 2).

Review
The demand is increasing for products and concepts for use in animal nutrition that will help keep our livestock healthy and thereby reduce therapeutic drug use with all its potential negative consequences. Brewers’ yeast cells contain a complex of ingredients that is composed of nutritive, prebiotic, ­bacterial and toxin-inhibiting, and immunological factors. Optimal results are achieved in animal nutrition if ­high-grade, top quality products are used.
Looking forward, products made from the yeast species Saccharomyces ­cerevisiae will become increasingly important thanks to the diverse and simple application possibilities, and their safety with respect to both animal nutrition and the environment.

References available on request