Do anyone know if you can give the Marek's vaccine older birds? I have heard of people giving older birds marek's vac. The bottle says how to vaccine in day old chicks but, I want to see what the oldest age you can give it.
You can vaccinate later but it may have no effect.
Every day past day old, the vaccine has less effectiveness.
The reason is that it is in a race with Marek's in the environment. It takes time for antibodies to develop and if exposed to a strain of Marek's they're susceptible to, it won't work.