A veterinarian told us one day "All racehorses have ulcers, but only 4% can suffer, and this is always reachable."
This comes a lot from their very energetic diet that is given to them for their training. In particular, dry oats. Adding this to the possible stress that some racehorses may have due to their respective character. So yes, many race horses have ulcers but once their diet is changed when they arrive in the circuit of reconversion (often a diet less rich and complemented with supplements), ulcers disappear on their own. If the ulcers persist, and the horse suffers, there are very good products that solve the problem.
All The Best,