Riding in the snow is a great workout for a horse.
On trails.. I'd be very careful. It is feasible, yes, but if those trails are popular there is bound to be quite a bit of ice. Just take your time and make sure your horse is nice and relaxed or otherwise under control at all times.
If you aren't shod, you could probably put shoes on but I'm not sure if that would be better or worse than going barefoot. Depends on your horse..
I used to ride in snow all winter long when I was living north. Not in MD though... Horses went barefoot and we never had issues with slipping (however we never run or even trot on ice, just the snow).
I ride all year round. Winter is more often bareback because it's warmer :) For the most part, I stay off the roads in the winter because they are often slippery. I ride in on bush trails and in my small fields. No shoes, no problems and no amount of snow stops me. But I am getting wussy in my old age -- I tend not to go out anymore when it gets to -15 celcius. I have a circulatory problem and my hands get dangerously cold then.
If horse has shoes on you would need to have sno pads to keep the snow from balling up in them. Around here, snow is really wet and sticky, so balls up in the shoes. But we only get snow two or three times a winter.
We have snow nearly 5 months of the year, barefoot seems to work best unless it icy then it's just too risky to ride. There is shoes with removable caulks & snowpads. That is best discussed with your farrier as there is disadvantages to using those as well. Posted via Mobile Device
Coming from snowland I ride my horses in winter,no shoes. Only real issues is snow too deep,it being too cold outside or when we get melting temps making hard icy snow just makes thinks harder for them, then we just don't go
About the snow balling in their feet - if you keep moving at a brisk enough pace, it just flies out. If you can maintain at least a working trot for a majority of your ride, it won't cause any discomfort as the snow will fly out of their feet.
We ride all winter while it's snowy - but the minute the ice hits, I'm outta there.