Exercise is as important as diet to maintain both health and good weight. To encourage exercise, get a package of paper lunch sacks. Lay one on its side. On the first day, put a thin layer of alfalfa on the side of the sack.
Flatten the sack, roll it up like a cinnamon roll and tie with raffia. Drop it on the floor in the bunnies’ space. They’ll probably spend several hours tearing it apart and getting every last bit of alfalfa out of it.
Do the same thing the next day at about the same time of day, but use something else – parsley, for example, and drop the sack in a different location.
At around the same time each day, put something different in the sack and drop it in a different location. When the rabbits begin anticipating the sack, start hiding it behind things in their space. Then start hiding it on top of things in their space (like a low stool or cardboard box). Make it harder and harder, but never so hard that they don’t find it before they give up, so the rabbits have to run and jump up on things to search for it.
If you start this practice when your rabbits are young, you will find they’ll continue to run around searching for the sack even when they’re elderly.
By the way, rabbits usually love the snow and it’s perfectly okay to let them run in it for 10 minutes or so. Just don’t let them get wet and cold.