It's important to know how to choose a second dog and ensure dog and dog compatibility. How well your current pet(s) accepts a newcomer depends on their age, health, sex, genetics, and traits of instinct, size, personality—the list goes on and on.
Some dog breeds are more willing to accept other canines (or cats), while others can be downright dangerous. The safety and well being of your new puppy and older dogs must be addressed before you bring the “new kid” into your home and introduce to other dogs.
Although there are exceptions, terrier-type breeds developed to go after “critters” and other breeds with a high 'prey drive' may not be able to control their instinct to chase and/or attack your new puppy. Sighthounds such as Afghans, Greyhounds, or Scottish Deerhounds may also feel the urge to chase scurrying creatures and may see a small puppy as more of an object to be chased than a companion. Herding dogs chase joggers, bicyclists, sheep, and cats, for instance—it’s a natural instinct, so be prepared for careful training if you share your life with one of these go-getters.
Some dogs who were never properly socialized may have a difficult time adjusting to another dog in the house, especially if they don't know how to communicate with other dogs. However, in general, dogs can adapt, learn to get along, and even enjoy each other's company, with good guidance and positive reinforcement from their human companions.
Even friendly dogs could prove dangerous if there’s a great size disparity between the pets. An 80-pound pooch could accidentally sit on your Chihuahua puppy or hurt the smaller pet if play gets too rough.
On the other paw, a jumbo-size Great Pyrenees baby might injure your older Lhasa Apso when the puppy-pounces on their fragile frame. Study the breeds and talk with professionals to help you make informed choices. It can work but requires more supervision and care on your part.
Big bruiser felines can be dangerous for tiny pups. Feline predatory behavior prompts games of stalk and pounce that can lead to injuries if interactions with a new puppy are not closely supervised. Claws can injure doggy eyes and/or inspire canine retaliation. Once a cat reaches the age of 12-18 months or so, cats may lose their inclination to make new pet friends. They may show signs of aggression or simply hide and become a stranger in their own home.
Puppies can be overly eager to play and may not understand the boundaries of what constitutes rough play yet. They also may not know the warning signs for when a cat is not interested in that kind of attention. For this reason, cats may hiss or swat at a new puppy in attempt to communicate these things and in a sense say, "leave me alone!" If your resident kitties have had positive experiences with other dogs, they’ll be much more likely to eventually accept a new pet into the household. It’s very positive if your new puppy grew has also been properly socialized to cats, so they already respect the feline attitude. In all cases, initial introductions should be closely supervised, and it is a good idea to allow each pet to sniff around the areas where the other spends time before having a face-to-face interaction.
Cats should always be provided with a safe space to escape to during these interactions and should not be punished for growling, hissing, or swatting which are important warning signs that dogs need to learn. Dogs should be kept on leash and/or held to prevent them from chasing or attacking. Positive reinforcement, such as treats and toys should be given to both pets during these interactions when they are calm so they can see that good things happen when they are together.
Many factors can affect the compatibility of your pets, and ultimately, their individual personalities will be the real deciding factor. Some people suggest that it may be best to choose a new pet that’s younger than, and the opposite sex of, your resident pet. That means if you already have a male adult dog, introduce a female pup. This is not always the case, and many times, any combination can work with the right personalities. It may be helpful to consider things like your current dog's activity level, size, and temperament when looking for a compatible housemate.
If you have more than one dog or cat already, it's not fair to introduce a new pet to all of the cats and dogs in your household at once. Introductions should be done one pet at a time. Sometimes it’s love at first sight, but more often, the pets take days or even weeks to learn to accept a newcomer. For this reason, the new pup should be separated from other animals at first to allow for a slow, careful introduction. All initial meetings should be closely supervised and lots of positive reinforcement with treats and toys should be used to show all the pets that this is a good thing. Any time things escalate to where any of the pets are growling, playing too rough, or showing signs of aggression or fear, the interaction should be paused and the pets separated. In this way, it may take many small baby steps to introduce your new pup but your patience will be rewarded with a harmonious home. By planning ahead, you can choose the best puppy for both you—and the resident pets that also share your heart.