Appearing in Daleks of Manhatten/Evolution of the Pig Slaves were once human but beacuse of their low intelligence were turned into pig slaves by the Dalek Cult of Skaro. The Pig slaves would then be used to capture more humans, where smart ones would be used for the final experiment and the less intelligent ones would become Pig Slaves. Pig slaves only had a lifespan of just a few weeks, and their Dalek Masters did not care for their lives only using them for slave labour.
Although not intelligent, the Pig slaves gained super-human strength, due to their hideous transformation, and were said to be able to slit a human's throat with their bare teeth.
Most of the pig slaves (minus lazlo) died when the daleks plan backfierd, its unkown what happend to the bodies. Any surviving Pig slaves would of roamed the sewers until their short lifespan expired.