Mycotoxin prevention in poultry feeds through yeasts and their by-products

Poultry meat is one of the best sources of protein for the ever-growing global population. However, mycotoxin, a secondary fungal metabolite with low molecular weight, is a prominent global challenge associated with health and performance issues in poultry. In addition, mycotoxin is a major threat to meat, eggs, and its derived products, thus a major concern for public health. The financial loss due to mycotoxicosis includes increased mortality rate, reduced productivity, and extra management costs including prevention, control, sampling, mitigation, and additional labour.

Prevention of mycotoxin production

Mycotoxins production can be prevented by decreasing the expression of the genes responsible for mycotoxin synthesis and by constraining the growth of the fungi responsible for its formation. For instance, Pichia anomala, a species of ascomycete and teleomorphic fungi, produces 2-phenyl ethanol which inhibits the formation of Aflatoxin B1. The 2-phenyl ethanol acts by the downregulation in the expression of the genes responsible for mycotoxin biosynthesis. Furthermore, yeast-derived compounds such as Lachancea thermotolerans decrease and inhibit the synthesis of mycotoxins including ochratoxin A in a biological way by using it as a carbon source. In addition, ochratoxin A and aflatoxins are deactivated by volatile organic compounds produced by yeasts. Moreover, yeasts use a variety of anti-fungal defence strategies such as competition for resources and space, creation of volatile metabolites, suppression of spore germination, formation of siderophores, and production of extracellular lytic enzymes to suppress the growth of the mycotoxins.

Impact of yeasts on growth performance

Mannan-oligosaccharides are composed of complex carbohydrate molecules derived from the outer cell wall of Saccharomyces cerevisiae. A natural carbohydrate fraction derived from Mannan-oligosaccharides improves performance in the starter and grower phases in broilers. Baker yeast and Brewer’s yeast are the most common among all to have βglucans in their cell wall.

Supplementing yeast and yeast cell wall extracts to the diet enhances the body weight parameters, feed intake, and feed conversion ratio in birds challenged with Fusarium mycotoxicosis.

Supplementation of yeast-derived carbohydrates improves:

• growth performance,
• health responses,
• immune system function, and
• anti-inflammatory effects in broilers.

Dietary yeast culture plus enzymatically hydrolysed yeast cell wall at levels of 50, 100, 150 mg/kg improve average daily gain and feed efficiency during the starter and grower phases in broilers and reduce carbon footprint, which may contribute to the farm productivity, profitability, and the environmental sustainability.

Impact of yeasts on immune system function

Dietary yeast culture: Modifies the immune system functions such as natural and acquired immune responses. Yeast supplementation increases the antibody titres to Newcastle disease virus and elevated IgM concentration in the serum and secretory IgA concentration in the duodenum.

In addition, dietary yeast enhances the activity of lysozyme content in serum which activates the phagocytosis phenomenon in the broilers to combat the prevailing pathogens. The natural carbohydrate fraction derived from Mannan-oligosaccharides increases the area of goblet cells in the jejunum, enhances mucin production, and augments defence against pathogenic challenges.

Supplementing yeast cell culture: Has immunostimulating effects and increases intraepithelial lymphocytic count, and caecal tonsil secretory IgA, and the activity of CD3+, CD4+, and CD8+ in the blood and spleen in coccidiosis-infected birds. Yeast cell wall supplementation decreases the lymphocytic blastogenic response in the peripheral blood, increases the weight of immune organs including the bursa of Fabricius, spleen, and thymus, and upregulates proinflammatory cytokines like interleukin1β and interleukin 6.

Adding a combination of Mannan-oligosaccharides and yeast extract to the broiler’s starter feed: Enhances antibody titres against infectious bursal disease and infectious bronchitis virus. A diet supplemented with yeast-derived carbohydrates transforms the innate immunity in chickens infected with Clostridium perfringens by supporting the pro-inflammatory responses via T-helper cells.

• Mannan-oligosaccharides supplementation in the diet elevates the humoral immune responses and antibody titres against Avian Influenza and alters the intestinal expression of genes important for inducing cellular immune responses such as lysozyme, lumican, apolipoprotein A-1, and β 2-microglobulin.
• β-glucans supplementation in diets of broiler increases the cellular immune response and improves the production of macrophages and activity of chemotactic factors in the birds challenged with Salmonella enterica.
• The Saccharomyces cerevisiae-derived yeast supplementation induces lower plasma corticosterone and mitigates the physiological effects associated with the stress response in broilers.

Impacts of yeasts on gut morphology and microbiota

The inclusion of yeast and its derived products in broiler diets improves gut morphology and environment in broilers.

• Feeding 0.2% yeast cell wall extract in birds challenged with Fusarium mycotoxin increases duodenal crypt depth, goblet cell counts, villi height, and crypt depth ratio.
• Dietary supplementation of yeast beta glucans increases the villus height, crypt depth ratio, the number of goblet cells and the secretory IgA-expressing cells in the jejunum.
• Supplementation of whole cell inactivated Pichia guilliermondii in Eimeria-challenged birds decreases the Eimeria oocyst count and increases the activity of macrophage nitric oxide and the concentration of interleukin-1 in caecal tonsils.
• Yeast supplementation decreases the proportion of E. coli and Salmonella in caecal microflora during the post-coccidial challenge.
• In addition, supplemented diet with yeast reduces the number of coccidial oocysts.

Concluding remarks

Mycotoxin contamination in poultry feed is a major global challenge affecting feed quality, health and performance of poultry, and the public health. Yeast is beneficial to overcoming mycotoxin contamination by increasing digestibility of calcium, phosphorus, protein, and fibre, enhancing the growth performance, improving the immune system function and gut microbiota, reducing the number of pathogenic gut microorganisms, and decreasing poultry mortality.

However, further research is needed to determine the proper conditions that yield the highest benefit from using the yeast and to identify new cost-effective yeast strains with high antagonising performance. In addition, it is required to provide various tools for the food safety management systems to effectively distinguish mycotoxins.

Source: Article – Yeast and derived products: their uses in preventing mycotoxins in poultry feeds Yeast and derived products: their uses in preventing mycotoxins in poultry feeds. Published in the World’s Poultry Science Journal