Are you conflating the terms feed and grain?
Grain is the seeds of plants in the grass family. Feed is formulated from many ingredients to meet the dietary requirements of the animal for which it is intended.
I'm assuming you mean the feed is 17% protein because no grain has that much protein.
Feed contains grain but also other ingredients including soybean meal and synthetic lysine/methionine which bring up the crude protein percentage to acceptable levels plus a lot of vitamins, minerals and fats that are missing from grain.