Is it too hard on a horse to walk in snow, say a foot or so of it? What about more? We get a lot of powdery type snow and I don't want to overexert them.

I wouldn't send my two out in snow, because a foot or two would mean that peaks would be likely to be touching their belly :P In that kind of weather I would do my best to find somewhere to take them for a run, maybe shovelling some of the yard for them to be out.

We dont ever get that much snow. Maybe an inch or two but only for a day or so. I know that my horse does not like the snow one bit. I would not advise it.