Why is Horatio among the guards in the opening scene? He is the supervisor, so is there to make sure the others are doing their job.
To lend proof to the story of the two guards that they have spied a ghost.
It is his job

To lend proof to the story of the two guards that they have spied a ghost.

Explanation:

Horatio was among the guards in the opening scene so that he can lend proof to the story of the two guards that they have spied a ghost.

Horatio never had the belief that there were ghosts, therefore the guards told him to come along so that they can show him King's Hamlet ghost and therefore make him believe that there were ghosts.

normally working animals are domesticated and ruled by a master, a domesticator (tamer), to perform basic and important functions on a farm, for example. the value used in this context is animal labor in exchange for food. it is not so much a contrast to the story told by napoleon and the pigs, since the animals of that particular farm also performed functions on the farm through domestication. the only thing is that in this case, who rules them is a pig, also an animal, but very respected, to whom the other animals lent him submission. that's about a strong relationship of dependency between animal and owner.