The organic poultry starter I bought is not medicated, and the feed store didn't think any of the chicks had been vaccinated. There are no other chickens in the area, although we do live on a wildlife/bird refuge that has a large wild bird population (from golden and bald eagles, pelicans, ducks, geese down to grosbeaks, redwing blackbird, grosbeaks, sparrows, finches, goldfinches, juncos, woodpeckers etc etc etc). Should I be concerned about Marek's or coccidosis, and if I should be, is it possible to buy an additive and put it in the feed myself?