The most likely reason the author wrote this passage is to show that Napoleon will use extreme cruelty to stop a revolt.
This excerpt from Animal Farm presents the cruel method that Napoleon resorts to in order to break the hens' rebellion: he stops giving them food and orders the other animals in the farm to do the same. Moreover, Napoleon decides that, if any animal dares to feed the hens, the pig will punish this animal with death. In that way, Orwell wrote this passage to emphasize the fact that Napoleon is a ruthless leader and a tyrant and that his cruelty has no limits.