"That means the horse had a bath."
When a horse is feeling fresh, it doesn't mean they feel clean, or fresh like produce. That means they're feeling themselves. They're feeling good, they're energetic, and going for it. This could either be a good or a bad thing depending on the horse.
Fresh can have another meaning. Another meaning of a fresh horse is when they hadn't been ridden in a while. Perhaps they don't have a riding routine. They may also be fresh from not being handled in a while.
