The Impact of Mycoplasma in Laying Hens Focusing on Egg Quality, Immunity, and its Role in Predisposing for Viral Infections
The problems associated with the use of antibiotics in the poultry industry have led to numerous issues and have negatively affected animal health, followed by adverse effects on human health. Therefore, there has become an urgent need to find natural and safe alternatives that can replace antibiotics in poultry and livestock in general.
Yeast is considered one of the oldest microorganisms and is larger than bacteria. There are more than 700 yeast species, but only a few have been well characterized. The term “yeast” is commonly used as a synonym for Saccharomyces cerevisiae, since most experiments have been conducted on this species and it has been widely used in industry.
Uses of Yeast
Yeast has traditionally been used in poultry and animal rations as a growth promoter. Under normal conditions, yeast does not multiply within the gastrointestinal tract of the host; it disappears rapidly from the digestive tract after being removed from the diet.
Main Effects of Yeast
Numerous nutritional studies have shown that adding yeast to poultry diets at a rate of 2–3 g/kg leads to:
Cells of S. cerevisiae and their extracts (water-soluble derivatives of alpha-glucan) contain antioxidant substances such as glucose tolerance factor fractions and superoxide dismutase. These substances remove free radicals from the bloodstream. In addition, adding yeast to poultry diets reduces lipid rancidity.
Yeast and Heat Stress Reduction
Yeast can be added to poultry diets to reduce heat stress for the following reasons:
The small intestine contains Goblet cells that produce mucus and support nutrient absorption through the intestinal wall. Heat stress reduces the number of Goblet cells. Studies have shown that adding yeast to the diets of heat-stressed poultry increases Goblet cell numbers, thereby improving performance under heat stress conditions. Studies also indicated improved yeast utilization when zinc bacitracin was added.
While yeast is present in the digestive tract, digestive secretions such as enzymes and acids break down yeast cell contents, which are rich in water-soluble vitamins, minerals, peptides, and aromatic amino acids, providing flavor enhancement as well as stimulation of liver function and improved digestion.
Some essential minerals may be unavailable to birds when present in inorganic form. Providing them in organic form bound to organic molecules may solve this problem. The utilization of selenium and chromium can be enhanced by incorporating them into yeast during growth.
Selenium is important for immunity and fertility and acts as an antioxidant. Chromium plays an important role in reducing fat deposition in carcasses and lowering mortality rates in broilers.
Yeast Cell Wall Components
Yeast cell walls are rich in complex carbohydrate glucans (46%) and mannans (43%). These components play an important role in maintaining intestinal microbial balance, improving immune response, and enhancing meat quality. Yeast also acts as prebiotic, reducing pathogenic microorganisms while increasing beneficial microbes.
Adding yeast may increase the absorptive surface area of the small intestine by increasing villi length, thereby improving digestion and absorption.
Many studies indicate that yeast supplementation reduces pathogenic microorganisms such as Salmonella, E. coli, Staphylococcus aureus, and Entamoeba histolytica, while increasing beneficial bacteria such as Bifidobacteria and Lactobacillus, thus reducing bacterial toxins.
Mannan in yeast improves immune response by increasing interleukin-6 secretion and stimulating the release of mannose-specific binding protein from the liver, which binds to bacterial capsules of invading pathogens.
Mannan may also enhance immunity by increasing plasma IgG concentration or by modulating cell-mediated immunity. Glucan in the inner cell wall stimulates specialized glucan receptors on white blood cells and extra-vascular macrophages, enhancing host defenses either by increasing macrophage activity or through macrophage-derived cytokines.
Yeast and Mycotoxin Exposure
Whole yeast has beneficial effects in birds exposed to mycotoxins (aflatoxin) at levels of 500 ppb to 5 ppm. Adding yeast at 0.1% reduces the adverse effects of aflatoxin on growth rate, liver weight, and serum albumin and total protein concentrations. Other benefits include increased antibody levels against Newcastle disease, with more pronounced effects in ducks.
Adding yeast at 0.9–1 kg per ton of feed improves egg production, fertility, reproductive organ weight (ovaries and testes), and hatchability by reducing embryonic mortality in flocks fed aflatoxin-contaminated diets.
Dr. Enas Hammad
Researcher – Animal Health Research Institute – Mansoura Branch Laboratory
Agricultural Research Center – Egypt