There were some videos a while back on a butcher torturing pigs in a slaughterhouse, which was leaked and showed inhuman practices. The pigs were squealing and grunting in absolute horror as they were tortured. It scares me to know exactly what emotions they were displaying during the torture.
While I don't know what happened in that case, was it worse than castration without anesthesia? Or is this fear you have more about the human intent than the effect on the animal?