How to Determine Compatibility of a Second Dog

Two dogs nose to nose

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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, gender, 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, as well as adult furry wonders, must be addressed before you bring the “new kid” into your home and introduce to other dogs.

Breed Considerations

Although there are exceptions, terrier-type breeds developed to go after “critters” may not be able to control their instinct to chase and kill your new puppy. Sighthounds such as Afghans, Greyhounds, or Scottish Deerhounds may also feel the urge to chase scurrying creatures.

Other dog breeds have been developed to take advantage of predatory behavior, but stop short of killing. 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.

There are always exceptions, but Kerry Blue Terriers, American Pit Bull Terriers, and other aggressive dog breeds may not get along with another canine. Most dogs follow the lead of the human family member they respect, though, and if YOU say the new guy is okay, King often accepts and endorses your decision.

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Size Matters

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 old-lady Lhasa Apso when the puppy-pounces on her arthritic 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.

Chihuahua standing in front of Border Collie
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Cat Considerations

Big bruiser felines can be dangerous for tiny pups. Feline predatory behavior prompts games of stalk and pounce that can turn deadly for helpless pups or traumatic for browbeaten dogs. Claws can injure doggy eyes and inspire canine retaliation. Once a cat reaches the age of 12-18 months or so, Tabby loses her inclination to make new pet friends. She will either do her darnedest to get rid of any interlopers you introduce or simply hide and become a stranger in her own home.

Cats are less likely to object to young puppies, though, and seem to recognize and be more forgiving of babies. 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 up around and has been properly socialized to cats, so he already respects the feline attitude.

Dog and cat
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Sex Appeal

As a general rule of “paw,” it works best to choose a new pet that’s younger than, and the opposite gender of, your resident pet. That means if you already have a male adult dog, introduce a female pup. These combinations prove the least threatening to the resident dogs so they don’t feel their authority is challenged.

Opposite genders and ages also work well when introducing the new puppy to cats, because each wants different things out of life. A resident boy cat who wants to “own” territory won’t upset the new girl puppy’s preference for ruling all the toys.

It’s not fair to introduce a new pet to ALL 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 strangers. By planning ahead, you can choose the best puppy for both you—and the resident pets that also share your heart.