Answer is; He uses parody to imitate communist propaganda techniques.
Many Communism ideas by Karl Marx are part of "Animal farm" a literary work in which George Orwell ridicules ( creates sattire) Communism ideologies taking place in Russia at the time, the U.S.S.R and also the Soviet Union. Characters like Mollie, Mr.Jones, Benjamin or Moses are based on real people who was participáting in communism at that time. In this pasage of chapter one we are told that Clover the horse the animals start to sing "Beasts of England" and the other animals join in. The song would be later on changed.