Symbolism, Imagery, Allegory
It's not going too far to say that white slave masters treat black people like animals in this book. And you can see this in the way white men will use dogs to hunt down runaway slaves. Dana finds this out the hard way when she tries to run away from the Weylin plantation and realizes, "Another dog found me later, though. It came racing toward me through a field and over a rail fence, barking and growling." Luckily, she uses a trusty stick (again with the stick) to repel the dog, adding, "I turned to meet [the dog] almost without thinking, and clubbed it down as it lunged at me" (4.12.35).
Later in the book, Alice Greenwood is badly wounded from the bites she got while trying to run away with her husband Isaac. The only reason any white people have a problem with this, though, is because Alice's money value as a slave gets lowered when she can't walk properly anymore.