When we buy our own food, most of the products have an expiration date or a best-by date. Most of the better dog foods have an expiration date or best-by date also, but Kentucky Equine Research indicates that horse feeds are not required to have these dates on the label. Many will have the manufacturing date on them and some may have a best-by date, but it is not mandatory. It is difficult to determine the significance of a best-by date because the storage of horse feed is sometimes in less than desirable environments and this will affect the best-by date. Therefore, horse feed may not still be okay to feed up until the best-by date depending on the environment where it is stored.
Products maintained in a cool, low humidity, and pest-free environment may be okay to feed after the best-by date while those stored in a hot barn in heat and humidity may not be good to feed even up to the best-by date. Extruded feeds probably have a longer shelf life than sweet feeds containing molasses. Regardless, it is best to store feed in a cool low humidity environment, which is difficult in hot and humid climates. Placing feed bags in containers off the ground helps rodent and insect infestation.
Another important issue is feeding corn straight out of the field. Corn is a great feed source for horses but it can contain a fungus that produces a poison called fumonisin. This poison causes moldy corn poisoning and it is almost always deadly, so it is never a good idea to feed corn to a horse unless it has been tested; all of the major feed companies test their corn before including it in the feed. So if you are using a product containing corn for your horses, make sure the corn is tested, and never feed corn directly out of the field.