In order to unlock this achievement, you need to play an empire that is able to set foreign species to Full Slavery. This is only possible if you choose Xenophobe or Fanatic Xenophobe as your ethic. With full slavery enabled for a species, set Livestock as their slavery type in the Species screen. Do this for five species you conquered or obtained by other means. Careful: There is also an option to use a species as livestock if you purge them. Thies does not work. You need to select livestock as slavery type not purge type.