Living with pigs means defilement.
"When he had freely spent everything, a severe famine struck that country, and he found himself in dire need. So he hired himself out to one of the local citizens who sent him to his farm to tend the swine. And he longed to eat his fill of the pods on which the swine fed" (Luke 15:14-16)
For reasons of cleanliness, Jews were not allowed to eat pork. The fact that the prodigal son not only lived with the pigs, but longed to eat their food would have disgusted Jesus’ audience. Moreover, living among the pigs signifies a defilement of appearance, while wanting to eat their food illustrates a defilement within.
+© Bartolomé Esteban Murillo | Wikipedia PD