* What type of show are you talking about? There are many different kinds of horse shows, each with their own rules:
* English Disciplines: Dressage, Hunter, Jumper, Equitation, etc.
* Western Disciplines: Reining, Cutting, Barrel Racing, etc.
* Other: Pleasure classes, trail classes, etc.
* What is the horse's age? Some shows have age restrictions for horses.
* What is the horse's level of training? Shows often have different divisions based on the horse's experience and skill level.
Once I have more information, I can give you a better answer.