Yes, you are not going to have much sunlight in mid winter MN and the temps are so low that I would not want to put a house raised pup out for long even in sunlight.

I would give him vitamin D3 and some cod liver oil in his food. Both of those should help his feet tighten up since it is the vitamin D he is lacking. You can buy it pretty cheaply at the grocery store for people, vitamin D is vitamin D, and I am sure there is cod liver oil there too.

Here is a video of a talk about vitamin D and how it helps our health --

http://www.youtube.com/watch?v=hiGBVDcbFVk

Interesting that they say anywhere north of Atlanta does not get enough sun in winter to give enough vitamin D.

Good luck with your pup and let us know how he is doing.