It comes in two parts. In Part I, he talks about various ethical issues. This comes from the site:

Peter Singer explores how controversial or compatible his views are with religious thought and in what sense his ethics is informed by a naturalistic or Darwinian understanding of the origins of life. He discusses the value of human life as regards end-of-life questions such as doctor-assisted suicide, and offers justification for the involuntary euthanasia of severely disabled infants. He details what it means to be genuinely “pro-life.” And he shares his views on stem cell research and abortion, arguing how that even though abortion is killing a human life, it is not unethical. He also explains what qualities of life would make killing it unethical.

In part II, he talks about Vegetarianism specifically. Here’s the summary from the site:

Peter Singer defends vegetarianism, arguing that we should give equal consideration to all “beings who have interests.” He draws ethical distinctions between human fetuses and animals, such as dogs and cats. He argues against “dominionism,” which is the idea that humanity is special, and that other animals were made by God for humanity’s benefit. He attacks “specieism,” and explains why he did not sign the Humanist Manifesto 2000. He describes factory farming, and the commercial imperatives that he says cause animals to be treated as mere property. He talks about the decision to become a vegetarian, and what keeps secularists and scientists from making the decision, in terms of the question he posed to Richard Dawkins at a recent Center for Inquiry conference. And he considers how working with the religious may advance vegetarianism in society.

Whether you agree with him or not, you must say that he has done a lot to philosophy.