Ferrets and cats are carnivores and predators. Don't assume that they will cohabit with natural prey such as rodents, rabbits, and birds. To avoid unpleasant accidents, these species should never be left with an unattended ferret or cat. Ferrets have been introduced to and cohabited safely and happily with many kinds of pets, most commonly cats and dogs. The first few times ferrets are exposed to other family pets there should be close supervision. The dog or cat can be allowed to observe the ferret safely shut in its cage, where the animals can see and smell each other but not touch. Ferrets like to tease other animals by nipping at their feet or tails, or running underneath them and grabbing them by the neck or belly and hanging on. These are ferret games that initially alarm other pets.
Barn cats can kill full-grown rabbits and have little trouble killing a naïve ferret – even house cats can easily kill a kit. However, cats and ferrets cohabit well when brought up together. Never assume that any adult cat will not harm a ferret if it has never seen one before. Remember that young ferrets are fearless and careless of their own safety, and will readily approach other animals. Supervise the cat and ferret whenever they are together until it is evident that the cat exhibits no stalking behavior. You may find that the ferret considers the cat to be a large, animated toy. Cat-riding is an exciting ferret sport, and attacks on switching tails provide endless amusement. Cats and ferrets living under one roof usually come to a mutually satisfactory arrangement. The cat may adapt by moving to higher ground and watching from a safe distance when the ferrets are enjoying their play-time.
It is wise never to expose a ferret to a terrier or other type of hunting dog likely to kill what it sees as small vermin. Some dogs will tolerate a ferret while the owner is present but will attack it when the two pets are alone. This is natural behavior for many breeds of dogs. Dogs within a breed vary widely and must be evaluated individually. No animal can be expected to have a conscience or be concerned about human values. Owners must take these responsibilities for their pets. Well-trained dogs can be taught to leave the ferret alone no matter what it does, but undisciplined dogs may have to be kept away when the ferret leaves its cage.
If the housing area does not overcrowd them, there is no limit to the number of ferrets you can house together. Some individuals may not be as sociable as others and, although it's a rare event in young ferrets, serious personality clashes may arise among older ones. Incompatible ferrets that have wrestling and chattering matches don't usually hurt each other, but may have to be housed and allowed out for exercise separately to avoid owner anxiety. Ferret skin is very tough and resists penetration of teeth and claws. Even after what seems like a pitched battle between two rival ferrets, there is seldom a mark on either combatant.
When new ferrets are added to an established group, you can expect a few challenges to the newcomer. Most senior ferrets accept young ones very well, and may be rejuvenated by the enthusiasm of a youthful companion. Older ferrets have much less stamina than a young kit or juvenile, and usually try to hide after a short time of very active play. Young ferrets don't wear out easily and the older one should be protected by returning him to his cage when he has had enough exercise.