Chronic ulcers will show up blood in feaces. Otherwise, they will take ages to eat a meal, taking a lot of breaks and drinking water in between eating. They can stand with their elbows pushed together, apparently this stance somehow reduces the pain , it can be really hard to keep condition on them and my horse was really girthy. These are the sypmtoms my horse presented with, but he wasn't super bad by the time I got him. So I am sure others will have many more symptoms to add.