Answer:
The animals in Animal Farm call each other comrades because the book is based off of history. Each animal represents someone or relates to a person in history. Animal farm was a parody of the Russian Revolution. Napoleon was supposed to be Joseph Stalin. Joseph Stalin referred to people as his comrades. The book is about the Russian revolution, therefore has communism has a central idea. Communism is all about how everyone is equal and has equal things, and everyone is friends. Comrades is basically another word for friends. The animals work as if they are in the military, they care and protect one another, they fight and adore each other as friends, as brothers and as comrades.