Quote: That's why the 28% works well for you -- you only feed it while the chicks are in the brooder. Their joints can take the higher protein at that age, in most chicken breeds up to 8 weeks old. But after that many breeds need to slow their growth, so the lower protein is needed to avoid future problems. Since most people don't like to, or forget to, change foods often as the birds age, the easiest recommendation for chickens is to start with 16-22 percent protein and continue until they need to go to layer ration. It's easy, and it works well because it gets done. For many dual purpose breeds it probably is ideal to start at 22-28% protein for the first 3-6 weeks, then decrease to 16-20% for the hens and 14-18% for the cockerels until 18-20 weeks, then put the hens on layer ration and the cockerels on either finishing ration or maintain on 14-18% for the breeders, +/- other changes along the way, depending on your breed and the use of the bird and your ability/willingness to adjust their management. But most people either don't want to have to keep up with all that, or forget, so despite being ideal it doesn't work for many people because it doesn't get done.
Free ranging tends to help balance out their diets also, although that is not an option for everyone. The birds can concentrate on eating grass or on eating bugs (or mice), as they wish, to increase or decrease their protein levels. The extra exercise helps their skeleton and joints develop properly.
It's amazing how important the details can be when you try to push the envelope. I've mostly raised English breed chickens -- Dorkings and Speckled Sussex -- and have found that these breeds, in my hands, do best when given some fish in their diet. It makes sense to me -- these breeds were developed in England and fish scraps were a common ingredient to give to the chickens on the English farms. They thrive with the extra animal protein. Then I tried it on some Barnevelders. Big disaster! The pullets did fine, but the cockerels grew too tall too quick, and every one was lame by the time they were 6 months old. It makes sense -- Barnevelders were developed using many breeds, including the Croad Langshan, which has very tall and stately roosters that do best with slow and consistent growth between 3-10 months. Had I looked at the breed's history and development before deciding on their management I never would have added fish to their diet after 8 weeks, but I didn't stop and think about this being a different breed. I just did what I had always done for my other chicks, without stopping to realize that I had customized my management for a specific breed.
One thing that's great about chickens and turkeys is that they can thrive on so many different management styles. Most of the time we only run into trouble when we try to push the limits, like I do with my Dorkings, and accidently apply it to a group that can't handle it. But that's how we learn, and hopefully improve.