I can only speak to the USA, but in my area the number one crop in this area is dent corn and soya. Of the corn grown here 40% goes into ethanol production, and 36% is used for animal feed.
Commercial poultry production heavily relies on grain -- typically corn. It's the primary ingredient in the processed feed overwhelmingly used for commercial poultry, as seen in this typical mix.
We absolutely grow crops specifically to feed livestock. And this is ignoring the 52 million acres used for alfalfa and hay-grass.