Even if your older dog or cat has lived peacefully with other animals in the house, there is no guarantee that a new puppy or kitten will be welcomed, or even tolerated. Some benign older animals will readily accept any pet brought into the home. Keep in mind that even the calmest dog or cat may be concerned at the appearance of a new puppy or kitten. So when you bring a new puppy or kitten into the home, your older dog or cat will need extra attention. He needs to know that you still love him and that the newcomer is not threat to his position in your household.
Your New Pet
Chances are your new puppy or kitten will be curious about his new surroundings and its occupants. Your new puppy or kitten may see your older pet as a new playmate and be ready to make friends, or your puppy or kitten may be shy.
Either way, it is best to isolate your newcomer when you first bring him home. Be sure to choose a room in neutral territory, and not in a room where your older pet sleeps or eats. Allow the puppy or kitten to explore a bit while you supervise. Then leave the newcomer alone for a short time so she can become comfortable in the new surroundings. This will also allow you time to reassure the older pet.
Animals get to know each other by smell. Therefore, don't be alarmed if you older pet spends a lot of time sniffing at the bottom of the door of the newcomer's room. This is normal. After a day or two, you should be able to determine what the older pet's reaction to the puppy or kitten is. A dog anxious to meet the new pet will scratch at the door and wag his tail, while a cat will purr and generally act curious or friendly. If your dog growls or barks at the door, or if your cat hisses and seems upset, it would be best to wait a few more days before attempting further interaction.
Take It Slowly!
When your older pet seems ready, introduce the pets by opening the door just wide enough so they can see and smell each other. Be certain that you stand close by to supervise. Gradually open the door wider for short periods of time until they have adjusted to looking at each other without becoming upset. This procedure may take several days, but it is usually successful.
Alternatively, replace the closed door with a baby gate. Again, be certain that you stand close by to supervise.
The first time the two pets meet face to face should be short and, hopefully, calm. If the older pet is a dog, proper restraint, such as a leash, will prevent him from chasing and scaring the newcomer.
Most important, don't force the issue. Let the animals go as close, or stay as far away, as they want. Repeat short introductions as often as necessary, until the animals are able to stay comfortably in the same room, with supervision. Don't expect instant friendship - that takes time.
A Place for Everyone
Your older pet needs to be reassured that the newcomer will not take over his territory. Therefore, don't allow the newcomer to take over a favorite sleeping or eating place.
Don't expect your older pet to be willing share his possessions, either. Animals are often possessive of their food and feeding dishes. Ideally, since the puppy or kitten requires an appropriate puppy or kitten food for its developing life stage, separate feeding dishes should be provided, preferably in a different room for a while.
Monitor mealtimes to prevent either animal from pushing the other away from its plate. Since most puppy and kitten foods are recommended for the first 12 months, it may be a good idea to continue feeding your newcomer in a closed room for awhile.
Equip the newcomer's room with a bed, water dishes, and toys. Kittens should also be provided with a scratching post and a litter pan. Two or more cats in a household often do share a litter pan, but many adult cats do not appreciate sharing with a kitten, at least until they are better adjusted. Providing your kitten with its own litter pan should help prevent your adult cat from starting to soil in inappropriate areas as an act of rebellion.
Friends, Friendly Enemies, or Foes?
It may take a year or more for your older pet and the puppy or kitten to become totally comfortable with each other. They may never become friends, but may simply learn to tolerate each other. Even if they remain standoffish, most pets appreciate another warm body in the house when their owners are not there. Over time, the majority of pets find a workable relationship, even if they are not best friends!