"Those animals are the slaves of the pigs."
Translation:Những động vật đó là nô lệ của những con heo.
Because they are not saying specific slaves, like for examples if you want to distinguish the slaves of someone from the slaves of another. The important thing is that they are slaves of the pigs.
A better translation maybe would be "these animals are slaves of the pigs", although I'm not sure since I am not a native English speaker.