Horse's ears are very, very sensitive. They can hear the "snap" of a carrot or the rattle of a grain bucket at the far end of their pasture. As the delicate internal auditory structure of the horse is designed to help him hear the slightest hint of a threat and just as we would wear ear protection at a concert or around heavy machinery, we also need to protect our horses' ears from damage associated with load noises. Enter earplugs for horses!
Just as in the human species, equine hearing can deteriorate with age, but ear protection can protect and prolong that hearing. Ear plugs also can help your horse from shying or losing focus and will help him keep calm during show day.
Ear plugs range in price and design, so it would be best to try them on your horse at home before entering the show area. Most disciplines allow plugs but many do not allow the net/plug combination. Check your rule book before ordering.