They build resistance to Cocci after about 16 weeks. You could feed them medicated fee until then and switch all of them to non medicated. Watch them for several weeks after moving off of the medicated feed to make sure they do not get sick.
okay and also I noticed my feed store has corrid, is that a treatment just in case?
My favorite chicken book and a must have for any chicken keepers library is "The Chicken Health Handbook by Gail Damerow. Published in 1994, it is indispensable for health related issues in plain speak. It also has lots of good info on management, feeding and housing.
I just learned there is a new edition coming out in January. The '94 edition can be had on half.com or amazon for very little.
Everyone has coccidia. It is everywhere. There are different strains. Most people choose to use medicated. The medication is a thiamine blocker and does nothing for anything but coccidiosis. I have rarely used it. A little coccidia exposure will make them resistant. The best defense is to keep the bedding bone dry and the feeders at least half full and you won't have to worry about it. It is a protozoa that has a multi stage life cycle. It can't live in a dry environment. If the bedding is wet, the coccidia will prosper. Then if the birds need to search the bedding for food, they'll ingest too much and be overwhelmed.
Another defense is probiotics. Either from a probiotic in the water/feed or fermented feed.
Vaccination is normally for Marek's disease- a virus completely unrelated to the protozoa coccidia. Vaccination for coccidia is relatively new and very few hatcheries do it.
Feeding a grower for a mixed flock of layers and non-layers is the best bet.
Never feed layer (4% calcium) to birds that aren't actively laying.
thank you! I read storeys guide to raising chickens and learned so much! I think I will look into that book! Thanks