information on differences of medicated feed and age of birds

[kidseieio]

We are having to switch to a medicated feed and are confused as to what is best to use. We purchased the purina start and grow but need something for our layers, any suggestions on what brand or type to feed? I have read that some medicated feeds cannot be mixed but what is best for my birds?? should I mix the grower medicated feed with my laying pellets? Also, whats the opinion on vaccinations for chickens? do most do this if purchased at a poultry auction?