Okay, firstly I have to thank you for introducing me to one of the more gripping stories I have tried to read.
That said, you seem to be labouring under a mild delusion, here.
See, horses (and ponies, too) can, and do, eat meat. It is a general assumption that a meat-rich diet would trigger some sort of intolerance reaction in a horse - but they get those if you change their feed too quickly anyway (except it's called colic. And the horse usually winds up dead), and seeing as how the steppe nomads of central Asia fed their horses a mix of fruit, grass, and offal without drastically impeding their ability to conquer... everywhere, we can presume that they did manage to adapt (granted, however, the smell of the horse droppings seems to be undocumented). And of course, we can't _know_ what effects strict carnivorism will have on the equin digestive system, as there are no records of a horse _ever_ doing that, and I really don't fancy the chances of anyone trying to pitch that experiment to an ethics committee.
Sorry for the rant, but this mistake is a really popular assumption and it sort of bugs me a little (just a little). Furthermore, it is a completely baseless assumption that herbivores are incapable of eating meat. Look at cows. We used to feed them meat, and we only stopped because it spread _disease_. Not because the actual diet itself was bad for the cow.