Not true at all. It can be effective any time as long as it is while they are exposed to the bug that causes Coccidiosis. Many chicks are not exposed to that bug until they are out of the brooder and on the ground. Even then some are not exposed unless that bug is in your environment.Since the medicated feed is only effective if started in the first couple days of life
There are some vaccines that give you immunity to certain diseases. Feed medicated with Amproleum is not one of those. It allows your chicken's body to develop immunity if it is exposed to that bug. That is a totally different thing.
I'll copy something I wrote a few years ago about medicated feed and Coccidiosis. It may clear up some misconceptions about medicated feed. If you have further questions please ask.
First you need to know what the "medicated" is in the medicated feed. It should be on the label. Usually it is Amprolium, Amprol, some such product, but until you read the label, you really don't know. Most "medicated' feed from major brands for chicks that will be layers uses Amprolium, but there are a few out there mostly for broilers, that use other medicines. I'll assume yours is an Amprolium product, but if it is not, then realize everything I say about it may not apply. And it is possible that the "medicated" is Amprolium AND something else.
Amprolium is not an antibiotic. It does not kill anything. It inhibits the protozoa that cause coccidiosis (often called Cocci on this forum) from multiplying in the chicken's system. It does not prevent the protozoa from multiplying; it just slows that multiplication down. There are several different strains of protozoa that can cause Cocci, some more severe than others. Chickens can develop immunity to a specific strain of the protozoa, but that does not give them immunity to all protozoa that cause Cocci.
It is not a big deal for the chicken’s intestines to contain some of the protozoa that cause Cocci. The problem comes in when the number of those protozoa gets huge. The protozoa can multiply in the chicken’s intestines but also in wet manure. For them to reproduce they need some moisture. Slightly damp isn't an issue, soaking wet is. Different protozoa strains have different strengths, but for almost all cases, if you keep the brooder dry, you will not have a problem.
To develop immunity to a specific strain, that protozoa needs to be in the chicks intestines for two or three weeks. The normal sequence is that a chick has the protozoa. It poops and some of the cysts that develop the protozoa come out in the poop. If the poop is slightly damp, those cysts develop and will then develop in the chick's intestines when the chicks eat that poop. This cycle needs go on for a few weeks so all chicks are exposed and they are exposed long enough to develop immunity. A couple of important points here. You do need to watch them to see if they are getting sick. And the key is to keep the brooder dry yet allow some of the poop to stay damp. Not soaking wet, just barely damp. Wet poop can lead to serious problems.
What sometimes happens is that people keep chicks in a brooder and feed them medicated feed while they are in the brooder. Those chicks are never exposed to the Cocci protozoa that lives in the dirt in their run, so they never develop the immunity to it. Then, they are switched to non-medicated feed and put on the ground where they are for the first time exposed to the protozoa. They do not have immunity, they do not have the protection of the medicated feed, so they get sick. Feeding medicated feed while in the brooder was a complete waste.
I do not feed medicated feed. I keep the brooder dry to not allow the protozoa to breed uncontrollably. The third day that they are in the brooder, I take a scoop of dirt from the run and feed it to them so I can introduce the protozoa and they can develop the immunity they need to the strain they need to develop an immunity to. Since I keep my brooder extremely dry and the water clean the protozoa can't reproduce so every three days I give them more dirt from the run so they get more protozoa and can develop immunity. I don't lose chicks to Cocci when they hit the ground.
There is absolutely nothing wrong with feeding medicated feed to chicks, whether the protozoa are present or not. It will not hurt them. They can still develop the immunity they need. But unless the protozoa are present, it also does no good.
If you get your chicks vaccinated for Cocci, do not feed medicated feed. It can negate the vaccinations.
I see no reason to waste that feed. You can either feed just it or you can mix it with something else.Should we just toss the remaining medicated feed?
You can get all kinds of differing opinions on practically any topic on this forum. Some people use all kinds of different things as supplements for themselves or for their chickens. Others don't. In my opinion if you have a known deficiency or a known condition some of these things can help. I take Turmeric on a doctors advice for arthritis, I noticed an improvement. If you don't have arthritis I would not expect Turmeric to treat your arthritis. Sounds silly doesn't it, to treat arthritis if you don't have arthritis. Yet many people do.Second question: During this research into the medicated feed, we also learned that electrolyte mix shouldn't be used for more than a few days at a time (the mix container did not say this anywhere, but we found the info on the rooster booster website). We had the chicks on it for about the first 10 days of life and they seem to be doing great; to be cautious though, after learning this, we switched them to plain water immediately. Would it now be appropriate to start putting ACV and herbs in their water as a natural supplement? Anything I might be misnderstanding here about the purpose of electrolytes for the birds' water?
In my opinion, as long as you don't get ridiculous and overdo it I don't think moderate levels of those things will hurt. Unless you are treating something specific I also don't think they will help but others will disagree. There is a whole industry out there telling you how much they will help so you will buy their product. There is a value to you if it makes you feel better even if it actually does no good. Just don't go overboard and overdo it.