Feather meal, animal feed, disposable diapers, and fuel for incinerators to heat/power plants are the existing uses that I know about from just Tyson Foods.
Food production is super highly optimized; I have to imagine this exists already in most plants.
This is consistent with my understanding that everything that can be sold out of an animal processing plant already is.
It used to be said that they use every part of a pig except the oink.
Yeah exactly, nothing from an animal is wasted, they're too expensive for that.
My in laws run a company that use hydrolysis to extract amino acids from waste feathers. Sells them to the pet food industry
one idea could be to produce less chickens
But how do we stuff our faces with excessive amounts of meat then?
Oh, that's been done; biofuel. It has actually become a bit of a _problem_ in some places AIUI; in countries where coal has been largely or entirely eliminated, it can end up being responsible for a surprisingly large fraction of atmospheric mercury emissions.