PETA goes on to mention that "in extremely crowded conditions, piglets are prone to stress-related behavior such as cannibalism and tail-biting, so farmers often chop off piglets' tails and use pliers to break off the ends of their teeth–without giving them any painkillers."
Animal Planet: Pig Genius
Marino, who is a vegan, and her colleagues have also studied chickens, finding evidence for cognitive, emotional and social complexity. Such ideas might seem laughable to some, but that's the point - our view of these animals tends to be that they are tasty yet non-sentient beings, only good for consumption. The reality is far from that view, according to this and other studies.
The researchers further note that we tend to put pigs in a lesser category than animals like dogs and cats, even though studies show pigs are just as intelligent and empathetic - perhaps even more so - than such pets.
The scientists next plan to study other factory-farmed animals, such as cows and goats. The research is made possible by grant money from Farm Sanctuary's The Someone Project, created to raise the public's understanding of farm animal intelligence and behavior.