ll chicks are vaccinated at the hatchery, and some chicks receive "booster" vaccinations after they have been in the grow-out house for several days. Have you ever wondered, "How do these vaccinations protect my chicks?"

The purpose of all vaccinations is to cause the birds to develop immunity to pathogens. Pathogens are things like bacteria and/or viruses. Marek's, Newcastle, Infectious Bronchitis, and Gumboro are diseases caused by viral pathogens that we normally vaccinate chicks against.

Vaccines against viruses consist of attenuated viruses that are either in cells or freed from cells. Attenuation means to reduce the ability of the virus to cause disease, that is, decrease its virulence. This is done by putting the virus through several replication cycles in embryonic cells. Then the virus is either freed from the embryonic cells or the vaccine is prepared using viruses still in the cells.

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