Burden not an animal with more than it can bear. We, truly, have prohibited such treatment through a most binding interdiction in the Book. Be ye the embodiments of justice and fairness amidst all creation.

Bahá’u’lláh, Kitab-i-Aqdas, #187

Educate the children in their infancy in such a way that they may become exceedingly kind and merciful to the animals. If an animal is sick they should endeavor to cure it; if it is hungry, they should feed it; if it is thirsty, they should satisfy its thirst; if it is tired, they should give it rest.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 374

If we say that these are effects of powers which animals also have, and of the powers of the bodily senses, we see clearly and evidently that the animals are, in regard to these powers, superior to man. For example, the sight of animals is much more keen than the sight of man; so also is their power of smell and taste. Briefly, in the powers which animals and men have in common, the animal is often the more powerful. For example, let us take the power of memory: if you carry a pigeon  from here to a distant country, and there set it free, it will return, for it remembers the way. Take a dog from here to the center of Asia, set him free, and he will come back here and never once lose the road. So it is with the other powers such as hearing, sight, smell, taste, and touch.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 304-305

It is not only their fellow human beings that the beloved of God must treat with mercy and compassion, rather must they show forth the utmost loving-kindness to every living creature. For in all physical respects, and where the animal spirit is concerned, the self-same feelings are shared by animal and man . . . The feelings are one and the same, whether ye inflict pain on man or on beast. There is no difference here whatever. And indeed ye do worse to harm an animal, for man hath a language, he can lodge a complaint, he can cry out and moan; if injured he can have recourse to the authorities and these will protect him from his aggressor. But the hapless beast is mute, able neither to express its hurt nor take its case to the authorities . . . Therefore it is essential that ye show forth the utmost consideration to the animal, and that ye be even kinder to him than to your fellow man. Train your children from their earliest days to be infinitely tender and loving to animals. If an animal be sick, let them try to heal it, if it be hungry, let them feed it, if thirsty, let them quench its thirst, if weary, let them see that it rests.

‘Abdu’l-Bahá, Selections from the Writings of ‘Abdu’l-Bahá, p. 159

Just as the animal is more noble than the vegetable and mineral so man is superior to the animal. The animal is bereft of ideality; that is to say, it is a captive of the world of nature and not in touch with that which lies within and beyond nature; it is without spiritual susceptibilities, deprived of the attractions of consciousness, unconscious of the world of God and incapable of deviating from the law of nature. It is different with man. Man is possessed of the emanations of consciousness; he has perception, ideality and capable of discovering the mysteries of the universe.

‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 240

Man is generally sinful and the animal is innocent; unquestionably one must be more kind and merciful to the innocent. The harmful animals, such as the bloodthirsty wolf, the poisonous snake and other injurious animals are excepted, because mercy towards these is cruelty to man, and other animals. For instance, if you show kindness to a wolf this becomes a tyranny to the sheep, for it may destroy an entire flock of sheep. If you give the opportunity to a mad dog it may be the cause of the destruction of a thousand animals and men. Therefore, sympathy to the ferocious animal is cruelty to the peaceful animal, so they should be done away with. To the blessed animals, however, the utmost kindness should be exercised: the more the better it will be.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 374