Napoleon orders the animals to stop singing "Beast of England" because he says that the revolution is over. The song was taught to the animals by Old Major, who believed in animal equality. Now that Napoleon is in charge, the ideas of Old Major and the revolution do not matter any more. Napoleon controls the farm and never intends to give equality to the other animals.
"It is replaced by another song composed by Minimus: “Animal Farm, Animal Farm,/Never through me shalt thou come to harm!”