Actually, in the ancient world when slavery was rampant, it was customary to treat slaves extremely well,. as long as they behaved. The reason for this was that they were perceived as being "property" and one does not damage a piece of property one owns for fear of it losing its value. At any rate, there are farms where animals are treated well. They admittedly do not get the right to roam too far, but, on the other hand, they are less likely to be savagely killed by predators' claws, nor will they suffer from thirst or starvation as much as they would do in the wild, and so on.