I'm not very good at reading teeth but I think closer to 8 than 20. They aren't angled out enough for an older horse plus in the second side picture it looks like that bottom tooth still has a triangular shape. Teeth are extremely stained though, makes you wonder what the heck the owners were feeding. My first thought was does that horse chew tobacco or what? LOL
Maybe that is what's throwing me off. Combined with the fact that he has a really hard time maintaining weight and muscle for what should be an easy keeper stocky pony type horse.
And to answer your question silage and moldy hay is what he had been eating. And for some reason he was soaked in gasoline - took a month to get the smell out!