The percentage of crude protein, lysine, methionine, crude fat, crude fiber, calcium min/max, phosphorus, salt and sodium are required to be on the guaranteed analysis tag attached to the seam on the bottom of the bag, opposite end from where you open it.
Some companies will include amounts of things like manganese, selenium, vitamins A, D3 and E, omega 3 and any probiotics on the tag as well but those aren't required.
If a feed is medicated it will be displayed prominently on the tag and the ingredient list will have the medication listed like amprolium or a sulfa drug.
It is a good practice to read the protein, calcium amounts every time you pick up a bag of feed, as well as the mill date.
One of Nutrena's all flock feeds recently went from 18% to 20% crude protein.
All of Purina's game bird feeds come in exactly the same bag. You have to read the guaranteed analysis tag because the maintenance chow is 12.5%, flight conditioner 19%, finisher 20%, layer 20% (with higher calcium), starter 30%. You have to read the tag. Mixing up 12.5% and 30% wouldn't be good.