I would never give a horse ACE before a show....I dont think it helps plus the risks tend to outweigh the benefits. If I was to give a horse something I would give them Equinamity EQ, it relaxes them without actually affecting their cordiantion or attentiveness. I am not positive it is legal at recognized competitions but for a schooling show there should not be anything wrong with it. Here is the website, http://foxdenequine.com/misc.htm#equinpaste, it is made by foxden equine. I love all of their supplements!