MadPriest has kindly directed traffic my way, so I'd like to devote a few postings to this and related subjects.
Concern for animal suffering can be found in the earliest writings of Hinduism, and the ancient Buddhist idea of compassion is a universal one; it embraces animals as well as humans. Our Western traditions are very different. Our intellectual roots lie in Ancient Greece and in the Judeo-Christian traditions. Neither of these is kind to those who are not of our species.
Among the rival schools of thought in Ancient Greece was that of Pythagoras, he of the famous theorem. Pythagoras was a vegetarian because he believed that the souls of dead people migrate to animals, and he didn’t want to end up eating his own grandmother. That’s more or less what it amounted to. Pythagoras however did not have anywhere near so many followers as Plato and Plato’s pupil, Aristotle, and it was the school of Aristotle that eventually became dominant. Aristotle taught that nature is a hierarchy in which those with less reasoning ability exist for the sake of those with more reasoning ability. Thus plants, he said, exist for the sake of animals, and animals for the sake of man, to provide him with food and clothing. An extension of this was that, in human society, the less rational barbarians exist to serve as slaves to their more rational Greek neighbours. Aristotle was, of course, Greek. Nice one, Aristotle.
Because, unlike Aristotle, we really are nice, we no longer follow him in applying the aforesaid logic to human beings, but our attitudes to non-human animals have barely changed at all.