Where are you located at?
What breed(s) of cattle do you have? Where are they from (did you buy them locally)? I have read that cows in more northern climates develop a thicker skin to deal with the harsher weather. I have also been told certain breeds hold up better than others in northern climates.
What BCS or condition are they in? Fat cows will not have any problems with those temps. Thin cows will require more attention.
What kind of hay?
We have rain right now, but it will be snow by tomorrow and then down to the teens and single digits after that. The problem I have is the rain will soak them and then it will get cold. That is hard on cows. Might even be worse than -15, if they are dry. I suspect they will be fine if you are taking good care of them. Might make chores a little rough the next few days :cowboy: