Animals don't have reason, which is crucial for understanding rights, and in consequence to be a moral being. Wolf doesn't act wrong when it kills sheep. It cannot do right or wrong because it cannot act in accordance with any moral principle, it doesn't know any concepts (self-ownership, privite property and so on), only feelings, sensations, instincts. If you don't understand Rothbard explaining natural law, read Kant instead, he was true moral philosopher and true libertarian.
RE: Vegan Anarchy: Do animals have the right to life, liberty & the pursuit of happiness?