It might no longer be true for the cows that have been breed for producing lots of milk. I guess most of them might still be able to survive outside during the winter, but I suspect that their milk production will be strongly affected.
It depends on the breed for sure, but as a rule of thumb when you're talking about the 40-55 latitude band, they're more comfortable/gain weight easier in the winter when it's cold outside than in the summer when it's hot outside.
