Your best bet would be a combination of things, start at home by putting a small piece of the pool chlorinating tablet in you water trough, put it in something plastic like a cup and sink it if it set directly on the steel you will get corrosion on the metal.This will also help with moss and algae in your trough.
Add something to change the taste and smell of the water at home, coolaid, firewater, powdered gator aid, or molasses.
At the show filter the water and add the same flavoring you used at home, should drink.