Pale skinned ones might not but Large Black, Oxford Sandy & Black and Tamworth might be a different proposition. All outdoor pigs need shade and a shower or wallow in hot weather. I've got a GOS with 10-day old piglets that's spending the day outside in a shaded concrete run in preference to her sty (it's 27 degrees here today). I usually shower the adult pigs with tepid water every 45 minutes when it's that hot but I don't want to soak the piglets so I'm leaning over the fence and dampening her down with the watering can instead. Works a treat.