Chicken feed that is stored in a cool, dry place away from direct sunlight has a shelf-life of approximately 6 months from the date of manufacturing. Feed should never be stored directly on the ground, concrete, or metal as those surfaces draw moisture and may cause mold growth. Wooden pallets are preferred. If you desire the longest shelf-life possible, you can consider some of the small packages (12 lbs bags or less). Those typically have a shelf-life of 9-12 months because the packages are solid plastic and have less oxygen in them. And, if electricity-usage is not a concern, you always have the option of freezing your feed to greatly prolong shelf-life. If you choose this method, just try to thaw only what you need for a few days to help keep the feed fresh.
How do farmers do it using silos?
Silos work a couple of ways. A true silo would have the feedstuff (corn silage, chop, etc.) packed very tightly in the silo. Then the product is preserved using an inoculate that deprives the silo of oxygen. Because there is no oxygen, anaerobic bacteria begin to grow and push the pH of the product in the silo down to a level that prevents mold from growing. Because silos are deprived of oxygen, farmers know they are very dangerous and should only be used or serviced by a professional.
Fans to keep out moisture
Farmers also use a lot of grain bins which also look similar to silos. In this case the grain (e.g., corn) is left to dry in the field. Once the grain reaches a certain moisture level, usually less than 18%, it is harvested by a combine and then stored in bins. These bins usually have large fans that push air through the crop to help it stay very dry. Since the grain is devoid of moisture, mold growth is greatly reduced.
Keep the Feed off the Ground
For rodent control, you will need to store somewhere safe and secure. For example, I store my feed stock on a wooden pallet inside a completely enclosed workshop. I watch for any signs of rodents and, if I notice any activity, I put out traps to catch and eliminate them. The feed that I am actively using is stored in METAL bins in my barn. I highlighted metal because mice can easily chew through bags, plastic totes, or wooden barrels. If you notice any signs of mice near your barn or coop, put out traps.