One of the central themes of this great story has to be the way in which Mrs. Grimes tries to sustain animal life in all of its forms, both human and animal, by "feeding animal life." This focuses us on the relationship between humans and animals and the extent to which one is or is not more important than the other.
Consider her various actions in the story: she feeds the animals of the farm, the German farmer and his wife and her own family with apparently no distinction between them. In addition, it is interesting to consider how the men are presented in the story. They are very much like animals in the inhumane way in which they treat others and consider themselves to be the most important individual in the world.
When we think of how animals are presented, the contrast between animals and humans in the story is made more explicit. Note the way in which the dogs are bestowed with qualities that we would normally associate with humans, and certainly make them appear "better" than their human counterparts. This is highlighted by the way in which they do not eat Mrs. Grimes' body when she dies, whereas the human men in her life seem happy to metaphorically eat her during her lifetime, glad receptors of her strength and energy in feeding them.
Throughout the story, then, you might want to consider how humans and animals are presented, and the relationship between these two categories of beings. The story seems to present humans as being more animal and animals as being more human, which is of course a very interesting comment upon humanity.