Sounds like an induced scrotal hernia, it may have happend even if the castration had not been done, tho' surely the weight of the other pig was the cause here,..due to weekness in the abdominal wall a portion of the intestine pushes through the opening where the cords pass from the testes into the body, if you get to it soon enough, wash every thing, push the intestine back into place and sew or super glue the opening closed so that the intestine can't fall out again. but, if it goes too long the tissue can strangle (blood supply is cut off) and the section of gut will die. then the pig will die. That is if, it is worth the trouble to save the pig, keep him away from other pigs or it could happen again until healed and watch for infection. and be carefull when you lift heavy things it can happen to people too.