Coccidiosis is caused by the numbers of certain protozoa in the chicken’s digestive tract getting out of hand. There are different strains of those protozoa, each strain colonizes a specific portion of the digestive tract. Some attack more sensitive areas so they are more dangerous. Some protozoa in the digestive tract are good, it helps the chicken develop immunity to that specific strain, it’s when the numbers get out of hand that the chicken gets sick. If the chicken is exposed to that strain of protozoa for two to three weeks they develop an immunity to it but that does not give them immunity to any different strain.
The life cycle of that protozoa is that the bugs lay “eggs” (not true eggs but close enough for this discussion) in the chicken’s gut. It passes out the rear end. It needs about two days in warm moist soil, especially soil with poop in it, to develop enough so it can “hatch”. The chicken eats it when foraging and it develops inside the chicken. That’s a big reason that wet brooders, coops, and runs are dangerous, those cocci protozoa thrive in those conditions. The chicken eats enough so that the number gets out of hand. A dry brooder, coop, or run helps prevent the numbers getting out of hand.
All strains of Coccidiosis protozoa are not present in all soil. Some won’t have any of these protozoa, some can have several different strains. Coccidiosis is generally more of a problem in warm moist areas like the Southeast of the US. That doesn’t mean it can’t be present in a cool dry area, just that it is more likely to be present in warm moist areas. Areas around a waterer can stay moist.
I always suggest you check the label to see what medication is in your medicated feed. It’s almost always Amprolium but almost always does not mean each and every time. If it’s not only Amprolium but is something else or something else plus Amprolium, what I’m going to say about Amprolium alone does not apply.
Amprolium in the dosage in medicated feed does not prevent all the protozoa from reproducing. It greatly inhibits the ability of that protozoa to reproduce. It allows enough to reproduce so there is a constant supply so the chicken can develop the immunity it needs. If you have a wet brooder, coop, or run and feed medicated feed it is still possible for the chicken to get Coccidiosis even if you are feeding medicated feed. But medicated feed with Amprolium greatly improves your odds. That’s still not an excuse for a wet brooder, coop, or run.
What often happens is that chicks are fed medicated feed while they are in the brooder but have never been exposed to the protozoa that causes Coccidiosis. When they hit the ground and are first exposed to that protozoa the medicated feed is stopped just when it is needed the most.
I personally do not use medicated feed. I keep the brooder very dry and introduce dirt from the run to the chicks as soon as they learn to eat their regular food, usually Day 2 or 3 in the brooder. I feed them more dirt every three or four days to give them a steady supply of that protozoa. By the time they hit the ground they have developed the immunity they need.
There is nothing wrong with feeding medicated feed. It will not hurt your chicks. If you have a history of Coccidiosis it is probably a really good thing to do. But if they have not been introduced to the protozoa it does no good.
