In the book Animal Farm what are some examples of racism?

The pigs consider themselves superior to the other animals, and chickens and sheep are second-class citizens. 

As soon as the animals have expelled the humans, the dream of equality on Animal Farm begins to crumble.  At first, it is decreed that all animals are equal.  The animals make commandments to enforce this idea.  However, soon the pigs begin to rewrite history.  They consider themselves smarter and better than the other animals. 

An example is the milk and apples the pigs take for themselves.  Squealer insists that the pigs are brainworkers and they need special food.  The animals had expected to share these, but then the pigs take them. 

"You do not imagine, I hope, that we pigs are doing this in a spirit of selfishness and privilege? Many of us actually dislike milk and apples. I dislike them myself. Our sole object in taking these things is to preserve our health. Milk and apples (this has been proved by Science, comrades) contain substances absolutely necessary to the well−being of a pig. …” (Ch. 3) 

The pigs slowly take more and more privileges.  They live in the house, wear clothes, and even learn to walk on two legs.  Napoleon drinks alcohol.  He also raises the puppies to be his secret police.  

The sheep and chickens are considered stupid.  Napoleon even gets them to confess to false crimes in order to reinforce his reign of terror.  Most of the animals go along with the pigs because they are afraid or they do not know any better.  Soon, the pigs are more abusive than the humans were.  All commandments are replaced with one.  All animals are equal, but some animals are more equal than others.