Horses being such easily spooked animals I'd be wary of flying anywhere near them, even if the event organisers were OK with it or had no policy.
If I were to try doing it I'd want something unobtrusive and quiet. The Mavic Platinum would be a good choice as it is much quieter than almost any other on the market, and much smaller than that 2016 model mentioned which appears to need a suitcase to carry it.