If you want to be able to 'return' it, I'd contact the store and tell them you're a bit concerned that it's old, and that if you open it and it seems funky, you're going to want to get your money back, or a bag of timely feed.

I've heard Lusk say that if the feed is discolored, then you don't want to use it. Now, I think he meant that if you see some feed that is colored differently out of a bag of feed, that means some of the feed is spoiling. I say that because if the entire bag of feed has changed color, you wouldn't be able to know that.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."