My stallion has just turned three. he lost his four incisors at 2 1/2, they fell out themsleves. At three he should be loosing some caps just behind the incisores at the front. You probably wont be able to see but a good indication they are ready to come out is tooth bumps. I would get a dentist to check his caps if they already havent been checked as sometimes they need physically removing. ( my stallion had 3 removed last week )