I remember reading somewhere that whole grains store for quite some time, but that the processed feed doesn’t.
The processed food I buy fresh from the factory has an expiration date of 4 months. Mainly bc vitamins disappear in due time. If you can keep it dry in a special container it wont go bad but the quality decreases.
The freshly bagged grain mix has an expiration date of only 2 months. This is because the factory cant guarantee there is no life form in it. There is a possibility tiny eggs of * meal moths and dust mites are inside the bag. If the eggs hatch and multiply, they spoil the feed.
Buying from this factory has the advantage it’s really fresh and way cheaper than buying feed in the pet and gardening shop. The disadvantage is we have to buy 5 bags at a time. Buying feed together with someone who lives in the neighbourhood is the best of both worlds.
*not sure if google translated it right.