Avian eggs are the largest sources of nutrients required for the development of embryos and a great number of defense factors to protect embryos and neonates against specific infectious agents that affect their mother or against received vaccine. Chicken egg yolk contains the immunoglobulin IgY which is the main antibody in the blood of birds, amphibians, and lungfish. IgY antibodies are passed from mother hen's serum to its eggs. The recently 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 1/104 - 1/106 after one or 3 - 4 booster doses. Prepared IgY can be stored active under cool or in dried form for a year, and can be administered to birds orally in feed or water and 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 and also, denote its value in disease prevention and treatment in the field of the poultry industry.