Bicarbonate! Can feed a handful at a time and it really seems to settle the stomach. We feed it with a handful of chaff about 20 mins before we ride. Much cheaper to buy and works wonders with some of ours
Omeprazole is a great med that can be used every few days (talk to your vet) to prevent ulcers. It is the cheaper form of gastroguard. Also Acid FX is great!I use both on nervous TBs and they do a great job!