I haven't... Do you have a place for the pigs to shelter and get away from the sunlight as well as a place for them to roll around in the mud?
Mud can work as a natural sunblock as well as a cooler for the pigs.
Mine have never gotten burned. They have a 3 sided shelter, a mudhole that I fill with water as needed and shade cloth in one corner that they can go under and get out of the sun.