Introducing a new pet to the household is an exciting time. For sure, your existing dog will have some strong feelings about the new addition. If your dog is generally well-behaved, though he will probably accept the new addition quickly. You can help ease the transition by preparing ahead of time and introducing your new pet slowly and gradually.
Introducing a New Dog
The best way to introduce a new dog to your existing dog is by meeting in a neutral location with a fellow handler. Have a friend meet you with the new dog at a public park or other low-key spot so you can introduce the two. Let them sniff and socialize if they want. If they want to ignore each other, that is fine, too. Redirect aggressive behavior by either dog by walking both dogs in opposite directions for a few minutes, then meeting up again. Keep the interaction casual, and keep both dogs leashed. Once the two dogs are comfortable around each other, take them both home to allow them to get to know each other better.
Introducing a New Cat
Cats can be trickier to control than dogs, so rather than introducing them on a leash, set up one room in your house to confine your cat while your pets get used to each other. Put everything your new cat needs in the room, including food, water, a place to sleep and a litter box. Let your dog get used to the smell of your cat under the door. Several times a day, put your dog on a leash and let your cat out of the room. Don't force them to interact with each other, let your new cat explore her surroundings, and let your dog get used to the cat's presence. Once they seem to be willing to tolerate each other, you can let your dog off the leash -- but continue to supervise their interactions until you are sure neither will hurt the other one.
Some Things to Consider
No matter how much your dog enjoys his new companion, he may still feel possessive of his belongings. Before you bring the new addition to the family home, pick up your dog's toys, chews and anything else he may not want to share. Make sure you have a separate area to feed your new pet and plenty of comfortable lounging spots. Finally, if your dog is older or a low-energy type, and your new pet is young or hyper, make sure to give your existing dog a spot where he can get away from the new addition and rest in solitude. A new dog or cat who constantly wants to play can try the patience of even the most tolerant dog. Confine your pets in separate, secure areas when you're leaving the home.
Patience Is Your Virtue
It is important to watch for signs of aggressive behavior from either pet during the transition period. Stiff, slow movements, showing teeth, growling, staring at the other pet for a long period of time and, in cats, hissing and swatting, are signs that you should separate the pets for a bit. Be patient during this transition period; it may take your dog some time to get used to his new companion.