I am in North western Ontario and we ride outside all winter. Some of the things we do are as follows
- ride in the warmest part of the day
- dress in layers
- put winter riding stirrups on our saddles so we can wear our skidoo boots
- put those little hand and foot warmers in our pockets and boots
- often ride bareback because its warmer (we trail ride through forests mostly)
- warm the horses bit before we tack up or use a hackamore, bitless bridle, or halter
- if the horse is sweaty when we come back we put a fleece cooler on him to help him dry and prevent hiim getting a chill
- if it is extremely cold (-30 or more) we don't work the horses too fast or too long because of the theory (and I don't know if it is true) that really cold air could damage a horses lungs and we don't want to take that chance
- always be aware of the footing, don't take the horse faster than safe for the footing
- be aware that sometimes a heavy crust on the snow could cut the horse's legs as he breaks through it .
I can't think of anything else right now although I am sure I am forgetting some. I took lessons one winter in an indoor arena and to be honest I found it colder and much less appealing than being outside. Outside you have the sunshine and the brilliant blue skies and dazzling white snow.