For the ventilation to work properly, we have to drive at a certain speed. When it's warm, we reduce the number of pigs in our trucks so the ventilation is better. However, when it's warm, it's warm, and the animals release heat. There's no possible airflow in an enclosed area if the truck isn't moving, so the temperature rises, which poses an additional risk.
At times, we have had to pass through certain areas where a road was closed, for example. In the middle of winter, another phenomenon occurs: the animals on the outside risk frostbite, while those in the middle of the truck are too hot.
Passive ventilation balances temperatures inside the truck.