If you believe that only humans domesticate other animals and also only humans kept slaves, then you need to read this.
Well, we humans have company, besides us, ants are the only other species to domesticate other animals. Many species of ants, domesticate aphids. They also shepherd them by taking them to the tender growing shoots of plants. The aphids suck the juices from these plants to feed themselves. Now ants will "milk" the aphids by stroking them with their antennas on their abdomens to stimulate them to release sweet liquid called 'honeydew'. When it is about to rain, the ants herd their livestock below the leaves so that they are not washed away. In exchange for their honeydew, ants provide protection for the aphids by attacking insects or parasites that threaten the safety of the herd. They also ensure that they are well fed by carrying them to new food source when the host plant is sucked clean. Also ants will often tear away the wings of aphids to stop their "cattle' from flying off.
Some ants like Polyergus, enslave smaller formic ants. They employ the smaller ants to take care of their young ones. The Polyergus, cannot care for their brood, because of their sharp mandibles. So they raid and steal the pupae of nearby ant colonies. When they emerge from their cocoons, the "slave ants" start to nurse the brood and perform other colony duties. To maintain a steady workforce, raids are conducted every month or so.