Enotes has a whole page discussing the style of this novel. You can view it at the link below. A few things to consider - first of all, the narrator of the story is a horse, so that definitely impacts the style. Sewell is able to accomplish this in a way that appears honest to the reader, getting them to consider things from the animals perspective. In addition to the point of view, Sewell's poetic descriptions and clear message are notable stylistic elements.