To a certain extent, there is some level of stereotyping in the book. This is done to bring out a couple of elements. The first would be that in stereotyping the animals, it helps to bring out aspects of their humanity, reflecting specific groups in our own setting. If the driving force of Orwell's work is to create a world that strongly parallels our own, then Orwell has to stereotype or group specific behaviors into singular characters in order to effectively forge this link. At the same time, I think that this stereotyping is critically important in order reflect how each particular animal represents some behavior in our own condition that is worthy of critique or better understanding. For example, in making Boxer one dimensional, a stereotype of the working man, the reader is able to understand how those who are working blindly for the government and place their trust implicitly within it can be so easily misled and manipulated. Napoleon is the stereotype of the evil genius and the autocrat so that the reader can sense these traits in their own leaders and be able to make connections that exist.
When creating an allegorical story, the author--to a certain degree--must employ stereotypes to make the characters fit into symbolic molds. If Animal Farm is to be a satire of the Russian Revolution, then the characters need to embody, for the most part, the traits of the players during that historical event. The horses Boxer and Clover are representative of the masses of people under rule in Russia. The animals are presented in the novel as loyal followers who remain primarily passive to the orders and decisions that are being dealt by the pigs. Certainly this is a stereotypical view of the masses of people during that time, and there were likely those who did not fit the mold. However, the place to explore this type of individuality is not a short allegorical novel. To do so would threaten the connections made between the novel and the historical event.