C HICKENS gut have diverse and complex microbial agents that have a critical function in digestability, nutrients uptake, development of immunity and pathogen fight. Then, gut health and bird productivty performance have been linked to falctuation in the intestinal microbiome components. Nevertheless, many factors affect the functionality, integrity and health of the bird's gut including the circumestannces, ration, and the intestinal microbiota. Pathogenesis of enteric and non intestinal illness may result in disturbances in the gut ecosystem; dysbiosis. Gumboro disease is a serious and infectious viral disease that affects chicks and is linked to significant morbidity and mortality rates. The bursa of fabrecius is the target organ of this immunosuppressive virus. Infectious bursal disease (IBD) virus causes histological lesions, alterations in immune cells, and changes in the microbial population by reproducing in gut-associated lymphoid tissue. Our review as part of Master's degree in poultry diseases, mainly focuses on the collection of published data the role of chicken microbiota in gut health, host immunity and chicken productivity in addition to factors affecting microbiota as age, sex, breed, maternal antibody, season, ration composition, antibiotics, relation between pathogen and intestinal microbiota with special reference to effect of IBD on gut microbiota ecosystem with role of probiotic and prebiotic in correction of dysbiosis.

A VIAN eggs are one of the largest sources of nutrients required for the development of embryos (proteins, fat, vitamins, growth factors, minerals and a great number of defense factors to protect embryo and neonates against specific infectious agents that affect their mother or against the received vaccine. The yolk of chicken eggs contains the immunoglobulin IgY which is the main antibody in the blood of birds, amphibians, and lungfish. IgY plays the role of mammalian IgG. IgY antibodies are passed from the mother hen serum to their eggs. The recently adopted technological methods facilitate the production and separation of specific highly purified IgY in hen's egg yolk, to be used as an alternative for antibiotics, and conventional serum-based techniques of antibody generation. Hens as IgY factory are kept under normal conditions of life and management without any stress, and they produce eggs containing the desired antibodies. Hens can be immunized by means of s.c or i. m by injection of 0.5-1.0 ml of antigen, to obtain antibody titers ranging from 1/10 4 -1/10 6 after one or 3 -4 booster doses. Prepared IgY can be stored active under cool or in dried form for about a year, and can administered to birds orally in feed or water as well as by injection.Our review as part of our Master's degree in poultry diseases, mainly focuses on the collection of published data on hen immunization, collection of eggs, preparation, separation, purification, and usage of the specific egg yolk IgY in poultry restoratives against different pathogens, maintain healthy respiratory, oral, and digestive systems, and also, denote its value in disease prevention and treatment in the field of poultry industry.