Also, for what it's worth, I believe there are two types of ulcers. Irritation ulcers can be healed by stopping whatever is causing the ulcer, ie. Bute, etc. The can be healed/soothed with slippery elm, and chia seeds.
The other type of ulcer is caused by H. Pylori bacteria. This bacteria is transmitted by flies. It's tough to knock out, and antibiotics are rarely effective. I believe treating with antibiotics makes the situation worse. Mastic gum is very effective in killing the H. Pylori bacteria. The most common type of ulcer in humans is caused by H. Pylori. By process of elimination, it should be easy to figure which type a horse has. If they have ulcers, but haven't been on anything that would cause them, than you have a good idea it's H. Pylori.