It’s not uncommon to get moths in grains/sweet feeds or hay products this time of year. The eggs are in there when the feed is milled and they hatch when the feed gets warm enough and is exposed to fresh air. Sweet feeds are generally not that great for horses (corn is pro-inflammatory and most horses just don’t need that much sugar in their diets. Long-term it can have a real impact on a horse’s risk for metabolic syndrome, insulin resistance, and laminitis.) However, in order to get rid of the moths you can do two things to help with the moth problem. First, get a commercial moth trap and put it up in your barn. Secondly, you can put any remaining feed into a sealed plastic bag and put it in a freezer for 12 hours. That will kill all the moths and their eggs. A horse can safely eat the eggs and dead moths, though.