It's a deeper question than it appears. Really.
Update: It was really cold on Saturday, and I made the comment that it was cold enough to freeze a polar bear's testicles. One thing led to another (aided by a couple of pints of beer), leading to a question that is currently baffling arctic naturalists everywhere! In my opinion, though, it is likely, because although sperm have to be kept below body temperature, I'm sure subzero temperatures would kill them dead.