Always start your chicks out with Chick Starter with 20% protien. There are several different brands to choose from but my feed of choice is always Nutrena NatureWise. Some chick feed is medicated to prevent coccidiosis.
When I first started having chicks I used the medicated feed thinking I was choosing what was best for them. But the truth is, it's medicine that they don't really need. They are better off building their immune system than they are eating medicine that they don't need. If they did have a problem with coccidiosis you can medicate their water instead. I haven't used medicated feed in years & I have noticed no difference at all.
When your chicks are nine weeks old they should be switched to a grower feed between 16-18% protein.
When to switch to a layer feed? Believe it or not, this is a controversial topic in the chicken keeping world. And I have my own opinion about it & yes, I have had to defend it a time or two...
I am big on not feeding things that are unnecessary. Layer feed contains calcium to help produce strong egg shells. If a chicken is eating layer feed and they are not laying yet, it can damage their kidneys. Even roosters. I only feed layer feed after a chicken has started to lay.
In the main flock, I offer a layer feed, a regular flock feed for roosters, and also provide crushed oyster shells. Oyster shell is a calcium supplement you can find at any feed store. The roosters prefer the flock feed naturally.
If you have a hen & chicks, provide the chick starter. It is fine for her until she starts laying again & will help her recuperate from her brooding time.
If your chickens become overweight they wont be happy & healthy. I limit treats to veggies & grass cuttings only. Really everything they need is already included in their feed, so they really don't require extras especially if they are free ranging. In the summer months I freeze fresh grass cuttings & extra zucchini for a special treat during the winter months.
Chickens love treats & we all love to see how happy they are when they get them. Just keeping things in moderation is key to a happy healthy flock.