I think it's not got for their digestive system as it then swells up lots once eaten. There's a higher chance of food poisoning, and without cooking the rice they don't get as much of the nutrients.
And I'm not sure about your analogy, it's a higher risk not certain death. Like saying I give...
Some things I do; Make sure there are no broody hens sitting too long in a nesting box, and it's not overcrowded.
You can spray the ground down a bit with a hose and any trees and plants they hang around/under (can spray the chickens too).
If you give them kitchen scraps, put them in the fridge...
You shouldn't feed them raw egg, not because it harms them, but because they can develop a taste for it and then they start helping themselves to all the eggs they lay.
I would call/visit the feed store and tell them they sold you out of date stuff and ask for them to exchange it for fresher feed.
Failing that, as long as it's not mouldy, I would still use it. Only a couple of small bags shouldn't take that long to use up, it shouldn't do them any damage, just...