why does black beauty bear all the pain and suffering?

One of the main messages Sewell attempts to portray through Black Beauty is that animals feel pain and suffering just as humans do: thus abusing animals is an unacceptable practice. However, as she demonstrates in the book, this practice is nonetheless widespread. All of the trials and torture which Black Beauty and his friends have to bear--the pain of the first breaking-in process, the unnatural feel of the bit in one’s mouth and the saddle on one’s back, the torturous check rein, the struggle of pulling overloaded carts and injustice of getting whipped despite one give’s ones best efforts—all of these are examples of abuse which the horses of the story face and which are widespread in society. In order to condemn this cruel behavior, Sewell has the heroes of the story constantly oppose this behavior. She also illustrates how it will be better of for both owner and horse to have a more peaceful co-existence. Finally, she asks the underlying question of the book: what would a horse say if it could speak? Multiple times in the book, the labeling of horses as "dumb animals" occurs. Yes, they are "dumb" in that they cannot speak. But that does not mean they feel no pain, it just means they have no way to express that pain. Here Sewell is giving them a voice, and is hoping that such an expression will be enough to change society’s behavior for the better.