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This development is, of course, not unconnected with the Pythagorean revival in philosophy. But by then the Pythagorean ban on eating meat had been reinforced by a philosophical tradition going back to Theophrastus and Xenocrates, the heads of Lyceum and Academy respectively in the late fourth century B.C. Theophrastus' work On Piety (much of which has been preserved in Porphyry's On Abstinence) presented a systematic argument against animal sacrifice, with an interesting theory on the prehistory of divine worship. Theophrastus cited Empedocles on the Golden Age (when Aphrodite ruled instead of Zeus, and "the altar was not drenched with the unspeakable slaughter of bulls"), and he claimed that the original offerings to the gods were made exclusively from the fruits of the earth. Theophrastus emphasizes the anatomical and psyholocial features that we share with the animals, above all, sense perception and feeling. He thus offers, for the first time, a philosophical basis for the notion of a moral community between us and the animals. On this view, we have the right to kill dangerous animals, but only in the same way that we have a right to protect ourselves against criminal human beings. Xenocrates, on the other hand, was concerned not only to protect animals but also to preserve the human being from contamination: animal food will assimilate the eater to the souls of irrational beasts. In Xenocrates we recognize a forerunner of the NeoPythagorean asceticism. Xenocrates; successor Polemon defended a similar view, and abstinence from meat became characteristic of the Platonic school. The writing of Xenocrates and Polemon are lost, but the Platonist case for vegetarianism, on a wide variety of grounds, is abundantly preserved in the writings of Plutarch, notably 'On the Eating of Flesh, Whether Aquatic Animals are more Intelligent than Land Animals', and 'On the Use of Reason by Brutes' http://books.google.com.au/books?id=5vi10r5k5eEC&pg=PA149&lpg=PA149&dq=pythagoras+banned+animal+sacrifice&source=bl&ots=0Lc1ia16G6&sig=g5KztIOdp5JJR7iEl4hEid6NJWw&hl=en&sa=X&ei=8TGdU8aIM8WlkQXykoHQBQ&ved=0CB8Q6AEwAA#v=onepage&q=pythagoras%20banned%20animal%20sacrifice&f=false

Diodorus Siculus reported that the Druids were “philosophers and theologians,” “skilled in the divine nature,” and able to communicate with the gods. Julius Caesar wrote that they had philosophical and religious beliefs pertaining to the “powers and spheres of action of the immortal gods”; that they had “much knowledge of the stars and their motion, of the size of the world and of the earth, of natural philosophy.” Strabo and Cicero said the Druids had the knowledge of nature which the Greeks called physiologia. Other ancient writers linked the Druids with the Pythagoreans. Diodorus, Ammianus and Valerius Maximus associated the Druidic belief in immortality with the theory of metempsychosis, making Druids “members of the intimate fellowship of the Pythagorean faith.” Some went further and derived the Pythagorean school of philosophy from the Druids. Iamblichus, for example, maintained that Pythagoras was acquainted with the Celtic mysteries, a statement confirmed by Clement of Alexandria, who in about AD 200 wrote that philosophy had been studied by the Druids before the Greeks. http://www.theosophical.org.uk/.../celts-and-druids-who.../