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An Almost Sure Way to Be Rejected by Your Dog

May cause failure to bond, even when you do everything right. Can also lead to bullying, aggression, and harm between dogs. While it isn't a foregone conclusion, animal behaviorists recommend against it. Plus, what to do if you've already crossed this bridge ...

littermate syndrome


  • Many dog behavior experts agree it’s a bad idea to bring home a pair of puppies from the same litter
  • “Littermate syndrome” is based on anecdotal evidence that often two siblings adopted together bond intensely with each other, to the exclusion of their human family
  • Puppies with littermate syndrome often suffer from intense separation anxiety when apart; conversely, one of the two may be dangerously aggressive toward the other
  • If you’ve adopted a pair of siblings, there are steps you can take to help them grow into well-socialized, balanced adult dogs

Editor's Note: This article is a reprint. It was originally published December 28, 2015.

Many experts and organizations in a position to know (for example, animal behaviorists, dog trainers, and rescue professionals), discourage dog guardians from acquiring puppy littermates. In fact, many shelters and breeders simply refuse to place siblings together.

The reason, according to certified professional dog trainer Jeff Stallings, writing for The Bark:

“Anecdotal evidence suggests that behavioral issues may arise during key development periods because the two puppies’ deep bond impedes their individual ability to absorb and grasp the nuances of human and canine communication.”1

In other words, canine siblings can be so closely bonded on a primal level, that if they go on to share the same home and family, that deep connection can inhibit their ability to learn how to communicate with their humans and interact with other dogs.

They wind up with a “muddled understanding of the world around them,” according to Stallings, which can create fearfulness and other undesirable coping behaviors.

The phenomenon is known as “littermate syndrome,” and it doesn’t occur in every single pair of littermates who are raised in the same home. However, it happens often enough that experts in canine behavior and the human-canine bond advise against bringing home siblings.

Signs of Littermate Syndrome

Some of the signs of littermate syndrome include:

  • Fear of strangers (people and dogs)
  • Fear of unfamiliar stimuli
  • High level of anxiety when separated even for a short time
  • Failure to learn basic obedience commands

Training two littermates is not just a matter of twice the work, but also the level of difficulty resulting from the puppies constantly distracting each other. According to Patricia McConnell, applied animal behaviorist and author of several books on canine behavior:

“It’s just hard to get their attention. They are so busy playing with each other … that you become the odd man out.

I suspect this indeed does have to do with social bonding to some extent, but I have seen pups of a duo who clearly adored their humans. Adored them. They just didn’t listen to them.

It seems harder to get their attention, harder to teach them emotional control, and harder to teach them boundaries. I imagine that we humans become more like party poopers that interfere in their fun with their playmates, not to mention that we are more tiring, because they have to learn a foreign language in order to communicate with us.”2

Another Potential Problem Among Littermates: Fighting

Sometimes littermate syndrome can take the form of non-stop fighting between the dogs.

Bullying and aggression between siblings seems to happen more often than between unrelated dogs, and it can get nasty. Many well-intentioned dog guardians have terrible tales to tell about the harm caused to one sibling by the other.

Shelters have stories as well of pairs (or one of a pair) being returned because the adoptive owner feared for the well-being of the sibling being bullied.

Unhealthy Emotional Dependence

Nicole Wilde, canine behavior expert and author of “Don’t Leave Me!” believes the separation anxiety between littermates is the result of hyper-attachment, which is also what interferes with the puppies’ ability to be properly socialized.

“People assume that having two same-age pups who play together and interact constantly covers their dog-dog socialization needs,” Wilde told Stallings, “but they in fact don’t learn how other [dogs] play and have no idea about social skills with other puppies, adolescents or adult dogs.

“Perhaps one puppy is a bit of a bully, which his littermate puts up with,” Wilde continued, “but his rude behavior might not be tolerated by a new dog in a new setting.”3

Many canine behavior experts feel it’s best to rehome one of the siblings when a pair is showing early signs of littermate syndrome, so that both puppies have the opportunity to grow separately into stable, balanced adults.

Since this can be a difficult time for the original owners, it’s often easier to have prospective new owners meet both puppies and decide which one to take.

Uh Oh … I’ve Already Adopted a Pair of Littermates. Help!

It’s important to keep in mind that it isn’t a given that every pair of puppy siblings will develop littermate syndrome. In fact, I’m sure there are many people reading here right now who are in complete disagreement with the advice of the experts I’ve cited.

With that said, according to Pat Miller writing for the Whole Dog Journal, there are things you can do to prevent or mitigate littermate syndrome if you’ve already brought sibling pups home with you.4

The goal is to keep the puppies from developing a counterproductive degree of emotional dependence on one another.

  • Two dogs, two crates — Miller recommends crating your puppies separately at night. The crates can be near each other initially, but one pup per crate helps each dog learn to adjust to being alone. The next step is to gradually increase the distance between the crates until the pups can no longer see each other.

    Make sure the crates are in bedrooms at night so the pups spend several hours in close contact with their human family members.
  • Two dogs, two training sessions — Train your puppies separately so that you can count on their undivided attention. Miller also suggests walking and socializing them separately to avoid ending up with a leader and a follower who looks to the leader – not you – for social cues, commands, and direction. This will help both pups develop into confident, independent adult dogs.

    Use training sessions to lavish attention and affection on one puppy, while the other works on a treat-release toy in his crate in another room. This will allow you to develop a bond with each puppy.
  • Two dogs, two play sessions — Miller suggests separating the pups for play sessions at least some of the time so that the less assertive of the two can come into her own.

    “For example, if you always play ‘fetch’ with the two together,” says Miller, “you’re likely to see that one pup repeatedly gets the toy and brings it back, while the other runs happily along behind. If you watch closely, you may even see the more assertive one do a little body language warning if the other tries to get the toy – a hard stare and stiffened body, perhaps.

    The less assertive one defers to her sibling by letting go of the toy and looking away. That’s a fine and normal puppy interaction, but it can suppress the ‘softer’ pup’s retrieving behavior.

    Unless you make the effort to give her positive reinforcement for fetching toys when you play with her alone, you might find it difficult to get her to retrieve later on in her training.”5

A Rule of Thumb for Most Dog Guardians: One Pup at a Time

As I mentioned earlier, littermate syndrome isn’t a foregone conclusion for every pair of puppy siblings. Genetics play a role, and certainly the knowledge and commitment of the dogs’ owner to raise two well-socialized, balanced individuals does as well.

However, the general advice given by professionals is: don’t do it. Instead, adopt a puppy who is most likely to fit into your lifestyle, and then focus on training and socializing your pup to insure she is comfortable in her environment and when she encounters other dogs and people.

Only after your puppy has grown into a well-balanced adult is it smart to think about adding a second canine companion to the family.

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