Animal shelters are places where unwanted pets and domesticated animals can be left, usually in the hope that they will be adopted by a new owner. One of the oldest and best-known is the Battersea Dogs Home in London (which also takes cats).
Bloggers writing about animal shelters may be promoting animals available for adoption, discussing the breeds put up for adoption, or sharing the experience of adopting an animal from a shelter.
Some bloggers are commenting on the cost of shelter charges, or their method of euthanasia (given that sadly many shelters have more animals than they can find homes for).