Hi!

Thought I'd chime in with my experience. I've fed non medicated chick starter from the 2015 and I've been raising chicks well, almost non-stop since then too, without issue.
Last August I had some eggs I was incubating and I also had a few broodies. We had an overnight stay for a medical appointment, and everything was being left to our kid while we were away. The one broody was wonderful and she'd take every chick I gave her so I gave her the newly hatched chicks I had in the house and from the silly broody who wouldn't stop brooding. They had feed and water in an xtra large kennel. Some chicks had been exposed to the outdoors...a few had not. Everything was great when we returned the next day. I moved her and the chicks into the large brooder that I'd been using for the incubated chicks...for a day or so because went straight back to combining. I moved her out with her first couple of chicks when I moved more chicks that had hatched out to the brooder.
Fast forward...a chick didn't look good one morning...by dinner it was dead. By my understanding...by using the broody, it introduced coccidi to the first chicks. She and those chicks exposed it to the brooder. I took her out, but the process had already begun. Those first chicks became massive coccidi producers which in turn got shed to every other chick I introduced to the brooder. It overwhelmed their systems and I began losing chicks. The particular
Eimeria strain my chickens carry doesn't show blood. It kills them very swiftly. Now remember, I'd been using this brooder for chicks a long time before this happened...so you can imagine my surprise. I normally introduce partially grown chicks to the flock and I've never had an issue with that.
From what I understand, medicated feed is specifically using a lower dose so the chicks can be exposed to coccidi which in turn gives them a chance to build resistance against the coccidi without dying or experiencing as much damage and scarring internally as being exposed without medicated feed. But that's only if good husbandry techniques are employed along with the use of the medicated feed. Using medicated feed doesn't compensate for overcrowded, stressed chicks in a dirty environment.
In my case, after bringing chicks to the vet...I was instructed to give the max dose of Amprolium for a specific amount of time. At this time the feed I had been using was no longer available. I tried two new different brands of chick starters...but I was still plagued with problems that presented as vitamin deficiencies like twisting faces/beaks, curled toes, leg issues. Not all the chicks showed these issues...but more than I'd like since this is not something I've dealt with prior.
Now, is it the feed? Or did the coccidi do that much damage that these poor birds were damaged beyond repair and couldn't absorb the proper nutrients due to scarring? I don't know...yet. I'm still feeling the fallout from this as I still have these birds.
I'm on my third chick starter; all the chickens actually like it (a first) and it's fine enough crumbles for the tiniest of my birds. I have a couple of chicks on it now and I will be converting to medicated once I move them out to coop.
Do I like the thought of using medicated starter? No, I do not. I don't like the idea of inhibiting the thiamine production in the chicks. But, now I view it as a tool to hopefully produce a premium chicken who "hopefully" doesn't suffer from unnecessary scarring and damage to their intestines. I'm hoping I'm giving my chickens a better start that will affect the rest of their lives in a positive direction.
My mind may change as this year unfolds and as I learn more how things turn out for my chicks this year. This is an ongoing learning experience for me. I didn't mean for this to turn into a novel...lol. But I did want to give my experience. Perhaps my experience can help someone else.
Food for thought...if a breeder sends exposed-to-coccidi chicks home with a new buyer, and that buyer puts the chicks in a brooder where they will closely encounter each other...should we be suggesting to them to use non-medicated starter? I think they "may" lose some chicks. I think we'd all hate for that to happen. Now that I understand the whole process better...my thoughts have evolved. I certainly don't want to see this happen to someone else if it can be prevented.