All my meat birds are raised in tractors that get moved as often as they run out of grass, every few days to once a week. They are not fed a commercial food, they are fed a mash that is made by the mill down the road from me. They grow their own grains and grind them up or leave some whole, like sorghum. I add a bit of their hog feed to my meat birds food, too. And I often feed starter all the way through to processing.
I feed a lot of rolled oats with whole grains, too. Whatever fruit the local farms have going to waste is brought home to add in the warm months and all our meat scraps go into the pens in the winter. We do not feed any cat food to them.
Not sure that the meat tastes any better because of it but I feel better because of it. My breeds taste different anyhow. We only eat our extra roos and that can be a lot! So far my Marans are the best tasting of all the breeds we have processed. I get some great breast, legs and thighs from them but even my banty Cochins can give me some great big chunks of breast. I think grass and dirt is good for them.