Best Lens For Equine Photography?

I'm an amateur photographer with a Canon Rebel T5i. I love shooting horse shows, and don't have any trouble with outdoor venues, but indoor arenas are a headache. I'm interested in upgrading to a lens that can handle the low light and still produce beautiful, high speed shots. What lenses would be best for this?

I've heard good things about the 70-200mm f/28, is this correct? Are there other options? Please help! Thanks!