|This is not our dog. We would never let one of ours get this bad. This pic came from Google and is just being used to make a point.|
The predominant reason, and the most simple one, is that the hair between the toes gets too long and collects snow. The more snow the toes collect, the wider the toes spread. The wider the toes spread, the more snow packs in between. This isn't good for several reasons.
First, it's not comfortable for your dog. Imagine having snow and ice between your toes!
Second, as it builds up, it forces the toes to spread as the dog walks. Long toe nails are also a problem. This can damage your dogs feet and cause them to walk on the backs perpetuating the problem.
Third, having long hair on the bottom of the feet makes it more difficult to get good traction. This could led to any number of muscular or joint injuries.
So what can you do about it? Well, the biggest thing is to keep the hair between the toes and on the bottoms of their feet cut very short. If you live somewhere where the temperatures are extreme in the winter, you can apply oils and products like Mushers Secret to help keep the snow from sticking and building up into a giant snowball. These can also keep the dogs pads from drying out and cracking open.
I haven't tried the Mushers Secret. After eliminating the problem by cutting, and keeping the hair short, I really had no need for it.
When you're out hunting this time of year, remember your dogs needs, and look out for them too!