A prominent view in contemporary political theory, the ‘associative view’, says that duties of justice are triggered by particular cooperative relations between morally significant agents, and that ‘therefore’ principles of justice apply only among fellow citizens. This view has been challenged by advocates of global justice, who point to the existence of a worldwide cooperative network to which principles of justice apply. Call this the challenge from geographical extension. In this article, I pose a structurally similar challenge to the associative view: the challenge from species extension. This says that the existing network of cooperation extends beyond the human species, to encompass some non-human animals, particularly domesticated dogs. In light of this, if one believes that (1) certain non-human animals are morally significant (i.e. objects of moral concern), and that (2) justice applies to fellow cooperators, one should also hold that domesticated dogs are owed justice in much the same way that our human fellow citizens are. I conclude by considering the implications of this argument for the associative view, and animal rights theory.