ELDRIDGE, Iowa — Sow 44733 had broken the shoulder of one of her pen mates, rousted another who was huddled in the corner and was chewing on the ear of a third.

Other sows in the pen sported abrasions, torn ears and bloody tail stumps — all souvenirs of her attentions.

It was that kind of behavior that led hog farmers like Tom Dittmer to isolate sows in individual stalls called gestation crates that are barely bigger than the pigs themselves.

“The reason the industry switched to crates wasn’t because we wanted to harm our animals,” Mr. Dittmer said. “We did it because we thought it was what was best for the animals.” The move also kept the price of pork reasonably low for consumers, he said.