Dr. Nabil Brandl writes:

I did an experiment to study pigs' movement by image analysis as an alternative to the manual method (video watching). I also did an experiment to measure pigs' dimensions to determine the space requirements of pigs. From these experiments, I found that if only two pigs were placed in a small pen, they divided the pen into two sections: one for sleeping and the other for manuring. But if you put six pigs in a pen with double the space given to the two pigs, the pigs will mix the sleeping and dunging areas together.

This means that if the pigs did not get their space requirements, there was more stress.