One may keep pets such as a dog, cat, or parrot. Even though the Sages prohibited Jews from trading in non-kosher animals, that prohibition only applies to those animals whose meat gentiles commonly eat; the Sages were concerned that if such animals were commonly found in Jewish possession, Jews might come to eat their meat. By contrast, there is no prohibition against trading in non-kosher animals whose meat is not commonly eaten. One may therefore trade in such animals and keep them for enjoyment and affection (Beit Yosef, YD 117; Birkei Yosef 2).
Some argue that since these animals are defined by halakha as impure, it is improper to keep them. This concern, however, is not mentioned by the poskim. These animals are called impure because their meat is forbidden to eat, and eating it spiritually defiles a person. But it does not mean that the animals themselves have corrupt traits or that keeping them causes spiritual harm to the owner. On the contrary, each species has its own distinctive quality, and the Sages even praised qualities found in impure animals, such as the loyalty of the dog and the modesty of the cat. It is therefore permitted to keep such pets.
A pet may not be kept when it causes distress to members of the household. Therefore, if a dog intimidates visitors, the owner must have it trained so that guests can enter the home comfortably and be received with proper respect (Shabbat 63a–b).
The Sages said that a person should not bring an animal into his domain unless he knows that he will be able to care for it properly (Yerushalmi, Ketubot 4:8). This includes feeding it, providing it with a suitable doghouse or cage, keeping its area clean, and vaccinating it when necessary.
When an animal under a person’s care becomes sick, the owner must provide the appropriate care. If the animal has a terminal illness and is suffering, it is better to put it down painlessly in order to spare it further suffering. If a person took in an animal thinking he would be able to care for it, but later realizes that he truly cannot, he should try to find someone else who will take proper care of it. If no such person can be found, he is not obligated to keep supporting the animal indefinitely; when necessary, he may put it down in order to spare it suffering (above, section 7).
One may feed live worms to aquarium fish without concern for the worms’ suffering. The prohibition of tza’ar ba’alei ḥayim applies when suffering is caused needlessly; when there is a genuine need, it is permitted. In addition, tza’ar ba’alei ḥayim applies primarily to animals with enough sensitivity to experience suffering more fully. With simpler creatures, the main concern is not to destroy them needlessly (above, section 1, the second principle). Similarly, one who needs to keep a snake may feed it mice. Although a mouse is more cognitively complex than a snake, feeding mice to a snake is permitted when keeping the snake serves a human need.
It is permitted, and even worthwhile, to maintain a zoo, since the animals receive proper food, and people benefit from seeing them and learning about them (Yabia Omer 4, OḤ 20).
It is permitted to provide psychological treatment with the help of animals. Through caring for an animal – feeding it, cleaning its place, and accepting responsibility for its well-being – the patient learns to take others into account and strengthens his confidence and sense of responsibility. Although patients who do not yet know how to relate properly to others may initially frighten the animal, become angry at it, or hold it too tightly, such treatment is permitted because it serves an important need and there is no intent to cause the animal suffering. The aim is to help the patient become someone capable of caring for the animal and treating it well.
