Some time ago when we lived in mid-north NSW (an area with wet summers conducive to coccidiosis), I used to raise batches of chicks in a concrete-floored shed.
I only raised 4 batches a year, and because I hadn't had problems in the past I didn't bother changing the litter (I was aiming for a sort of deep litter effect). Unfortunately deep litter is an artform in itself. At any rate, by the 3rd batch in the one season I began to see coccidiosis in the chicks even though they were on medicated starter.
All these chicks had been raised at 2 week intervals, and the weather was warm and humid. Even so I should have expected the medicated starter to work. But obviously the parasite numbers had overwhelmed the coccidiostat, or else some resistance had developed. It's also perhaps possible (without being a microbiologist I'm only wondering) that the coccidiostat in the feed had destroyed the microbe balance in the litter. Whatever the case, it was an eye-opener, and after that I began to think about ways of weaning my system off medications if I could safely do so.
However my first foray into unmedicated chick rearing was also problematic. The first batch went fine but the second developed cocci signs and had to be put on both medicated feed and a sulpha drug. I can see now what went wrong — it was management failure, pure and simple — but it sobered me into thinking I could never leave medicated feeds behind, whatever their limitations.
But my current chicks are just over 3 weeks old and doing very well on ground that has had chicks on it before. Not in high numbers, of course, and not for a few months, but it's certainly far from virgin ground. Moreover these chicks have eaten only very low amounts of medicated starter, and since going into the tractor have been fed the sprout diet with added meat meal, bandsaw dust, rolled oats and the odd dose of kefir, which is a fermented milk drink rich in probiotics. They haven't been in the tractor long enough to know for sure, but I suspect that they've already developed good resistance against coccidiosis. Furthermore, we've now had 5 days of light summer rain without them developing the telltale droopy wings or (a first symptom) going off their feed.
Next batch of chicks (which may not be for some time) I'll be raising in the same way, but the tractor will be in a new position to start with. In this way I should be able to limit the oocyst numbers while the birds' immune systems respond. Since coccidiosis is a terrible disease that can claim birds quickly, I'm not taking it lightly. But there are good signs so far as I head toward medication-free rearing.
After all, it's overuse of antibiotics that has ruined their effectiveness on germs like MRSA. As beef-producers head away from grass feeding into feedlot and end-stage fattening via pellets that contain antibiotics of their own (to control rumen pathogen overgrowth caused by a change to grain), it seems to me there is all the more reason to withdraw medications in favour of management and non-synthetic remedies wherever we can.
Relatively clean ground (not sterile), probiotics, lightly soured milk, judicious infection with small amounts of healthy adult droppings, and quality fresh feed may go a long way toward keeping chicks from developing coccidiosis in their first months of life.
But time will tell if this system can become permanent. Wish me luck!