mikey - "How could these two men do this to another human being ?"
Because they could.
It is possible for people of low intellect to regard someone like this poor man in the way they regard their animals - there to work with minimal food and shelter necessary to produce what they are on the farm for.
It is appalling, but if you look at it from the point of view of rational behaviour, you will only hurt your head.
This is behaviour by people of low intellignce, with no ability to empathise or understand outside themselves.
It is a horrible situation, but one has to feel pity for the perpetrators - I doubt whether they would consider themselves cruel or inhuman - such concepts are probably beyond their comprehension.