Another problem with feeding cat food is the lack of vitamin D in it. Cats and dogs are capable of converting vitamin D2 into vitamin D3, so D2 is what cat and dog food contains, as it's cheaper to source. Humans and chickens need vitamin D3, especially in the winter when there isn't a lot of sunlight. Chicken feed has vitamin D3 in it. I would just top up the feed with soy flour. For my chick starter I run my layer rations through a coffee grinder and add a few tablespoons of soy flour or soy milk powder, which are pretty much the same thing but for some reason, my Bulk Barn store sees fit to charge more for the soy flour than the powdered soy milk mix.