we had -15 here last week, and my girls was shivering & I was very worried about one of them who i thought may get phnumonia. The shed they are in is incredibly cold, even the water buckets were froze solid. I put single feece rugs on both of them, but decided to install a heat lamp instead, they dont mind wearing a rug, but the lamp brings temp up to +2 in the shed, which is far more acceptable apparently as the girls are much happier & no longer shivering.