Unfortunately, it may be too late to vaccinate for Marek's Disease. It is best done at 1-2 days old. Marek's Disease is very prevalent, and past that age, the chicks may already have been exposed. It wouldn't hurt to vaccinate, but it may not help.
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The most common vaccination that hatchery chicks receive is for Marek's Disease. Some hatcheries also vaccinate for Coccidiosis. However, they usually only do this if you ask them to in your order. If the feed store didn't specify to receive...