I believe the feed mills have an interest in selling feed. Not to say that the commercial feed won't speed up the process some or possibly have healthier birds, but there are plenty of people experimenting with other feeds and fermented feeds and don't have major issues. When we did meat birds some years back we lost some birds even on the commercial feed, 1 just died probably from bad heart the other 2 we killed early because they couldn't walk. I also believe people raised chickens for thousands of years before there was such a thing as commercial feed. When I do meat birds again I want to try a fermented feed and free ranging if they will free range, some have problems with the birds being either too dumb or too lazy to hunt their own food, then again I may go with a slower growing breed as well
I wanted to address the " I also believe people raised chickens for thousands of years before there was such a thing as commercial feed". - That is true, however, 1) they did not raise the breeds that we have today. 2) They lost a lot more animals, and general health was not as good. 3) They did not grow nearly as quickly or efficiently as they do today. 4) They had to have a supply of forage and grains, growing on the farm, to fill the diet needs of those chickens. 5) Layer birds only produced 1-2 eggs per week. There is a reason why feed mills were invented.....
"I believe feed mills have an interest in selling feed" That is a true statement. However, it is a very competitive market, and feed companies strive to offer better performance than a competing company. There is millions of dollars spent, every year, for advancements in animal nutrition. These advancements do make a difference. We are not just throwing something together, and hoping for the best. There is a method to our madness
To answer the main question in this thread- If you want the best performance, lowest mortality, and best meat flavor- 1) Buy a known high quality starter and grower ration for your meat birds. 2) Do not feed a Scratch feed!! It dillutes the amount of vitamins, minerals, and probiotics needed for an optimal diet. 3) Feed according to instructions on the feed label. 4) Allow access to pasture.
The rations, that feed companies manufacture, are designed to provide optimum results. Some farmers supplement with other things, and most of them know what they are doing. If you have time to do that sort of thing, and you know that you are not negatively effecting the diet, it is something that can be fun to do. However, pound for pound, you will not beat the formulations that are designed for growing meat birds.