It's best to house pet rodents individually because this prevents problems such as aggressiveness, unwanted breeding, and cannibalism of the young. If it's neccessaryto put more than one rodent in the same enclosure, keep the following in mind:
Popular Small Pets | Animal Planet
Assessing pain in animals, is similar to assessing pain in human babies, and relies on the observations of technicians, owners, and veterinarians. A notable drawback is observer variability and the interpretation as to whether an animal is in pain or distress. Knowledge of clinical signs associated with pain potentially provides an objective, rather than a subjective judgment. However, for such signs to be effective observers must have good powers of observation and knowledge of what is normal for the individual animal species. Rats and mice in pain may show decreased food and water consumption, weight loss, self-imposed isolation, self-mutilation and gnawing at limbs; rapid breathing, open-mouth breathing and abdominal breathing; increased or decreased movement; unkempt appearance such as a dirty, greasy or dull hair coat; abnormal posture such as a hunched back; dehydration, skin tenting and sunken eyes; twitching and trembling; and familiar signs such as redness or swelling around a wound or lesion. Recognizing distress is more difficult. The presence of disease, self mutilation, abnormal behavior, or failure to grow are obvious indicators of distress. However, we do not have simple, definitive measures of distress, and we believe the best approach is to use one’s intuition and sensitivity. Ideally, we should have an empathetic attitude and base our evaluation on critical anthropomorphism (25). A good strategy for assessment of pain and distress is to involve everyone involved with the pet rodent, as each person will bring a different focus to bear: owners “know” their animals and veterinarians possess clinical skills. Technicians are crucial in this identification because they know the biology of the species, including its relevant behavioral and physiologic responses. Furthermore, technicians are most likely to know when a hospitalized animal is “not right” and are likely to pick up changes in behavior, posture, appearance, or even the feel of the animal.
Selecting the small pet that's right for your home is no small feat
Smaller mammals, including hamsters, guinea pigs and gerbils, are relatively easy to raise. Most will thrive in a relatively small living space, and require fairly rudimentary care. Except for hamsters, which are solitary, it’s best to obtain young same-sex pairs. Regular, gentle handling promotes friendliness, but bites are possible should rodents feel threatened (especially hamsters). Surprisingly, rats make excellent pets due to their intelligence, larger size, and enjoyment of human companionship. Guinea pigs are also excellent kid-friendly pets.
Best For: Children of any age; a great "starter" pet.