I don't know, maybe some areas are more prone to worms than others.... My birds are organic and free range... Never had a worm problem.... All home make foods, plenty of greens bugs and so forth....
I strongly believe if one stays balanced with nature their is no need for all the chemical crap. Using those awful chemicals on a back yard flock? Why? Might as well go buy antibotic and chemical laced factory farm eggs then..
Come on you are not commercial operators with 10's of thousands of birds at stake.... Take a risk, be observant work with nature.. Get those chicks in dirt on day one!!! Dump all that medicated garbage... Go natural