I keep each separate bag of feed in a plastic tub. I do like to dump them out and look them over to make sure it is clean feed. I got one bag of hay pellets that had plastic bits in it once, and very occasionally I will find a bit of moldy feed in the bottom corners of a "new" bag.

"It's really quite amazing what a horse will do for you, if he only understands what you want. 
And it it's also quite amazing what a horse will do to you if he doesn't." ~ Bill Dorrance