The ranch hands are described in terms of beasts of burden throughout the novel. Lenny receives this treatment the most. His hands are paws. He apes George's actions. He moves in a "bear-like" fashion.
Slim must drown off 4 of the 9 puppies because of a lack of food. The men immediately respond to the dinner bell in a hurried fashion because there is never enough food. They even come running at the sound of the dinner bell which is an obvious allusion to the Pavlov's dogs.
Curly's wife and Candy are both mirrored by dog imagery. "Lulu" and "Shepherd" both show a relationship between their character and their function on this ranch.