Many farms use individual barrels or garbage cans to store one or two bags of feed at a time, and this method can work very well, provided that the lids close tightly to keep moisture and rodents out. Wooden or fiberglass feed bins are another time-tested way to go, although it should be noted that large bins allow more of the surface area of the grain within to oxidize and lose nutrients. They can be a hazard if you have small children who like to climb into things, however, so be sure to remove the latch. You can minimize the problems by keeping the feed off the floor on wooden pallets, and by ensuring that they're stored in a closed-off area. Warm, humid days and cool nights are the worst conditions under which to store feed.
Most farms have far fewer problems in winter than in summer.
E. Hay, too, suffers the loss of vitamins when it is exposed to air and light. All hay is best stored under a roof, and a three-sided hay shed often will pay for itself within a few years in terms of hay salvaged from losses due to weather. The increased fire hazard must be weighed against the convenience of being able to easily grab and feed hay bales without going to a separate outside storage area. If you do store hay in the same barn in which your horses are housed, pay particular attention to the ventilation in your loft. Air circulation is crucial in preventing heat buildup, so leave some room between stacks and avoid stacking right up to the ceiling.