@neil mock: "....we get night time frost from time to time."
No expert here, but we have had pet pigs, both pot-bellied and large farm breeds, for a few decades. We are in northern Minnesota with the temps that go with the region. All the pigs here are free-ranging and have appropriate
shelter and supplemental food when needed. Pigs that we've had have come from all over the US and have had no problem adapting, boars, sows, what have you. We even had a couple Ossabaw Island pigs that came from a breeding herd near Lake Superior after their ancestry had adapted them from Europe to that island in the south Atlantic off of Georgia. And of course the pot-bellies are originally from SE Asia and the Yucatans, a villiage pig from southern Mexico. Pigs are noted for being one of the domesticated animals that can go feral in a hurry......hence the wild pig populations increasingly moving north in the US that are derived from original escapes from domesticated situations.