Hey Deb, while I can’t give any treatment advice (I’m a former Vet Tech, but still nowhere close to a real DVM!), I can share a helpful Q&A I found on the topic of oral ulceration from our friends over at The Horse! You can check out the article here: http://www.thehorse.com/articles/16243/mouth-ulceration (they may require you to register, but it’s easy and free!). Hope that helps!
Rider, Runner, Stuff-Riders-Say-er, SmartPaker