I bed with straw and provide protective wooden liners against metal siding. Pigs have very little natural protection from the cold. They stuff frostbite very quickly and can also be killed by wind chill. Necessary precautions to take for cold weather transport include providing bedding and liners. I do not change stocking densities in hot weather.
Pigs have a very low tolerance to high temperatures and humidity.
Precautions reducing the possibility of heat stress include decreasing stocking densities, providing none or very limited bedding, ensuring maximum airflow through the vehicle, loading and unloading promptly and limiting any slops. Pigs should also be transported during the coolest part of the day. Some producers and transporters have sprinkler systems in their trucks to provide relief in case of emergency or extended wait for unloading.