i dont generally like to use my feed more then 3 months past the mill date...the date that it was milled/made. usually it is printed somewhere on the bag, generally near the threads.
Some people put it in the freezer?? but if you not using a bag in 3 months.. then wh y not just buy a new bag?? i go through a bag every 1.75 days UGH
It goes stale like a bag of chips, you will see the chins start to eat less and pick up a piece of food and throw it on the floor. They do that anyways, but they do it a lot when it's stale. You should find a mill date on the bag. I buy a 50 lbs bag of Purina Adavanced Nutrition Show Rabbit (PANR Show) I only have 4 chins and I keep it fresher in Hefty's XL utility zip lock bags
I store my Oxbow in a vittle vault airtight container - http://www.petsmart.com/product/index.jsp?productId=2811537
I order 50 lbs. at a time from Oxbow and they use a "best by date" on a sewn on label, which is 1 year from when it was actually milled. Since I sell some to members here, my 50 lbs. gets used up in a little over 1 month.