The Latin phrase "in ovo" means "into the egg". In medicine or veterinary medicine the phrase means the cultivation of viruses on embryonic tissue for the purpose of obtaining vaccines, as well as the method of vaccinating poultry against multiple viral diseases. Vaccination of chickens using the in ovo method - that is the application of the vaccine into the hatching egg before the hatching of the chick, was first described by Sharma and Burmester in 1982. They found that chickens that had been vaccinated into eggs on the 18th day of incubation (3 days before hatching) with a vaccine against Marek`s disease had better immune protection in three days after hatching than chickens vaccinated immediately after hatching. At that time, this method of vaccination was just an idea, but with the development of equipment with the mechanical implementation of vaccinations as well as with the development of new vaccines it became widely accepted in commercial practice. In order to achieve high hatchability and good immune protection, it’s imperative to vaccinate at the right moment. Good knowledge of the development of the embryo and key factors influencing the development is, therefore, essential. Another important factor is the vaccination site. The subsequent immune protection rate is strongly dependent on the vaccination site (air cell, amnion, alantois, yolk sac, embryo). Maintaining proper hygiene before, during and after in ovo vaccination is of utmost importance for successful vaccination.
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