Given the incredible number of chickens that are processed every single minute across the world, this shouldn't be surprising but it's easy to see why you might be surprised if you never considered where all the stuff that isn't meat goes.
https://en.wikipedia.org/wiki/Feather_meal
Manure is also fed to cows.
https://extension.missouri.edu/publications/g2077
"Poultry litter can be used as a feedstuff... There are currently no federal or Missouri regulations governing the use of poultry litter as a feedstuff"
Poultry litter has been banned as cattle feed since 2001, partially due to mouth and foot disease and BSE and to some extent animal welfare.