Animals (satta or tiracchāna) are sentient beings other than humans. The Buddha classified animals as being either born from eggs, from the womb, from water or spontaneously born (S.III,240). At other times he classified them as many-legged, four-legged, two-legged or legless (Vin.II,110). He said: ‘I know of no other class of things as diverse as the creatures of the animal world.’ (S.III,151; Sn.600). He also said that more beings are reborn as animals than as humans (A.I,36). Because animals have a limited capacity of comprehension and, thus, little chance to develop spiritually, and because the animal kingdom is dominated by the principle of ‘eat or be eaten,’ the Buddha considered it to be a distinct disadvantage to be reborn as an animal rather than as a human. Nonetheless, he acknowledges that sometimes animals set an example that humans could do well to copy. Once when some monks were quarrelling with each other the Buddha said to them: ‘If animals can be courteous, deferential and polite towards each other, so should you be.’ (Vin.II,162). Animals are sentient beings, capable of feeling pleasure and pain and, thus, worthy of sympathy and respect. Most religions say that we should love other humans. Buddhism broadens and universalizes love by saying that it should be felt for and expressed to all beings, however humble. The Buddhacarita says: ‘Empathy with all creatures is the true religion.’ (sarveṣu bhūteṣu dayā hi dharmaḥ). The earliest legislation to protect animals from cruelty and to provide reserves for wild animals was drawn up by the Buddhist monarch Aśoka in the 2nd century BCE. See Hunting.
The Great Compassion - Buddhism and Animal Rights, Norm Phelps, 2004.