A couple of years ago, prior to COVID-19, I would buy 4-6 months of feed if they were on a good sale. I never had any feed go bad. Just make sure you always use the oldest stuff first by using good feed rotation on your bags of stored feed. You don't want to buy a storage supply of feed to save money and then end up throwing it away because you forgot to check dates and make sure you feed the oldest food first.
Ditto on the lack of feed sales. Now the "sales" don't ever beat the quantity discount. The "regular" price went up $4/bag - so now the hunt is on to find the store that actually HAS enough in stock to GET the quantity discount. Sigh.