Antibiotic alternatives, yeast cell wall

      The poultry industry is currently facing an urgent need for alternatives to antibiotics, driven by the growing concerns over antibiotic resistance, residual effects in animal products, and the potential impact on human health. The overuse and misuse of antibiotics in poultry production have led to the emergence of drug-resistant pathogens, which not only compromise the effectiveness of disease control in poultry but also pose a significant threat to public health through the food chain. As a result, there is a pressing demand for safe, effective, and sustainable alternatives to antibiotics to enhance production performance and reduce the incidence of enteric diseases in poultry.

      For more than a decade, yeast and yeast fermentation products have emerged as promising candidates in the feed industry, demonstrating significant potential in improving the growth and feed efficiency of livestock, including poultry. Yeast, a unicellular fungus, and its fermentation products are rich in various bioactive components, with the yeast cell wall being a key source of beneficial molecules. The yeast cell wall is a complex structure composed of numerous polysaccharides, including mannans, chitin, β-1,3-glucans, and β-1,6-glucans. These polysaccharides possess unique structural and functional properties that contribute to their bioactivity and health-promoting effects in the host.

      Mannans, for instance, are heteropolysaccharides consisting of mannose units linked by glycosidic bonds. They have a high affinity for certain pathogens, such as Escherichia coli and Salmonella, by binding to the lectins on the surface of these pathogens. This binding prevents the pathogens from adhering to the intestinal epithelial cells, thereby inhibiting their colonization and proliferation in the gut. Chitin, a linear polymer of N-acetylglucosamine, plays a role in maintaining the structural integrity of the yeast cell wall and also exhibits immunostimulatory activities. β-1,3-glucans and β-1,6-glucans are known to activate immune cells, such as macrophages and neutrophils, through specific receptors on their surfaces, triggering a series of immune responses that enhance the host's resistance to infections.

      Yeast and yeast cell wall products exert their beneficial effects on poultry health through several principal mechanisms of action. Competitive exclusion and antagonism are important mechanisms by which these products reduce the load of pathogens in the gut. Yeast cells and their components can compete with pathogenic bacteria for nutrients and adhesion sites on the intestinal mucosa. For example, mannans in the yeast cell wall compete with pathogens for binding sites, effectively preventing their attachment and subsequent invasion. Additionally, some yeast strains produce antimicrobial substances, such as organic acids, bacteriocins, and hydrogen peroxide, which exert direct antagonistic effects against pathogens, inhibiting their growth and reproduction.

      Immunomodulation is another crucial mechanism. The bioactive polysaccharides in yeast cell walls, particularly β-glucans, can stimulate the immune system of poultry. They interact with immune cells, such as dendritic cells and lymphocytes, to promote the production of cytokines, antibodies, and other immune factors. This enhances the innate and adaptive immune responses of poultry, enabling them to better defend against enteric infections. Studies have shown that supplementation with yeast cell wall extracts in poultry feed can increase the number of immune cells in the blood and lymphoid organs, as well as improve the activity of immune-related enzymes.

      Yeast and yeast fermentation products also have an impact on digestive enzymes, which contributes to improved feed efficiency. These products can enhance the activity of various digestive enzymes, such as amylase, protease, and lipase, in the gastrointestinal tract of poultry. This is likely due to the presence of certain bioactive substances that stimulate enzyme secretion or act as cofactors for enzyme activity. Increased digestive enzyme activity promotes the breakdown and absorption of nutrients, such as carbohydrates, proteins, and fats, from the feed, thereby improving the utilization of feed and promoting growth.

      Furthermore, yeast and yeast fermentation products provide direct nutritional benefits to poultry. They are rich in proteins, amino acids, vitamins (such as B vitamins), and minerals, which can supplement the nutritional requirements of poultry. The proteins in yeast have a high biological value, containing essential amino acids that are important for growth and development. Additionally, yeast fermentation products may contain growth factors and other bioactive compounds that promote cell proliferation and differentiation, further enhancing production performance.

      In practical applications, numerous studies and field trials have demonstrated the effectiveness of yeast and yeast cell wall products in poultry production. For example, in broiler chickens, supplementation with yeast probiotics has been shown to increase average daily gain, improve feed conversion ratio, and reduce the incidence of diarrhea and other enteric diseases. In laying hens, these products can enhance egg production, improve egg quality (such as increasing eggshell thickness and reducing eggbreakage), and promote intestinal health.

      In conclusion, yeast and yeast fermentation products, with their diverse bioactive components and multiple mechanisms of action, represent valuable alternatives to antibiotics in the poultry industry. They can effectively improve production performance, reduce the incidence of enteric diseases, and contribute to the sustainable development of poultry production. Further research and development in this field will likely lead to more optimized and targeted applications of these products, providing greater benefits to the poultry industry.