Speckledhen, I do agree that living in an arid clime should initially reduce the the incidence of coccidiosis. We do have trillions of wild birds that possibly could have imported the avian species of protozoa into the site of the coop/run though?
We have always had many, many little dirty birdies that try to hang out in our barn. Thankfully, a busy group of small bird hawks (Kestrels) and roadrunners, tend to reduce the populations substantially. I can sterilize the inside of the run still being built though, although protozoal organisms can be wretchedly hard to eliminate. Once the coop/run is up it will be completely bird proof (half-inch x one inch wire). Our opportunistic/numerous packrats will also have a hard time burrowing under the concrete foundation and wire apron buried in the perimeter gravel. Point is....wild birds CAN bring in disease, even though packrats have their own "breed specific" species of Cocci.
I have always started my chicks in other states on medicated feed, just 'cause I am paranoid. When living in coastal GA (prior to NM) I never used any coccidiostats, such as Amprolium, or sulfonamides. The "teenagers" were well started, and very healthy when I bought them (mainly Golden Sebrights, with a few Quail d'Anvers). All of the birds were "free range" 24/7 too, giving them a pretty healthy existence.
I just don't want to lose any of our new babies (Yes, Yes,...I AM paranoid!)
Bine, You are sooo right, to try to build a good immune system. Good diet counts! If your chickens get exposed to the causal protozoal organism, you still might have a bad scene though? It also may be possible that acidifying the drinking water a tad bit might help the desired intestinal flora? Foster the Good Bugs,.. over Bad Bugs? Heck I dunno. Our water is extremely hard, with much calcium, originating from valley wells. The hard water makes it a PITA to grow plants, etc (and why we have a water softener in de house). Does altering water Ph help with healthy chip?