During pregnancy, they also are extremely irritable and dangerous, not only to their fetusus but to themselves and to their handlers. A sow left to wallow at will can injure herself, her unborn and her owners. They've been known to tear down fences and attack animals twice their size-- including two-legged ones.
Yes, little piggies raised as pets may not have such pronounced tendancies. But the bulk of confined PG sows are on commercial operations-- they are huge and produce huge litters. City guys who have dealt with a spouse or girlfriend with an extreme case of PMS have only the faintest idea.
Sows can also have extreme difficulty birthing. A cage or grillwork between them and the handler is not only an important aid, but an important protection when the piglets must be pulled out with forceps.
Pig penises are shaped like corkscrews. An old farm joke is "Why do pigs have so much trouble giving birth?" Answer: "They're screwed in."
Every day you learn something new. Thanks.