Upon reading Patricia Leslie’s email, I knew I’d be replying with disappointing news. “We were planning to adopt one puppy, but the breeder said that raising two sisters would be easier.” Leslie had contacted me after reading my blog post about littermate syndrome, in which profoundly bonded siblings have difficulty relating to humans and other dogs.

“After we brought the mixed-breed girls home at nine weeks, their behavior grew completely out of control. My husband and I could not get their attention for more than a second or two, as if we weren’t even in the same room. And then they started displaying alarming fearfulness of people and other dogs.” I made an appointment to meet Patricia, her husband Karl and the puppies the next day at their Richmond, California home.

Many dog behaviorists, trainers, breeders and shelters discourage adopting siblings. Anecdotal evidence suggests that behavioral issues may arise during key development periods because the two puppies’ deep bond impedes their ability to absorb and grasp the nuances of human and canine communication. Since fear is the default reaction to odd or unfamiliar stimuli in dogs, this muddled understanding of the world around them can lead to impaired coping mechanisms later on. Many factors influence behavior and not all siblings raised together will exhibit signs: Littermate syndrome is a risk, not a foregone conclusion.

Littermate Syndrome

Common Signs
Signs include fearfulness of unfamiliar people, dogs and other novel stimuli (neophobia); intense anxiety when separated even briefly; and difficulty learning basic obedience skills. In some cases the two dogs fight incessantly. Over lunch recently, veterinarian and dog behaviorist Dr. Ian Dunbar and I discussed raising sibling dogs. “It’s a disaster waiting to happen for the littermates because they don’t get socialized to other dogs or people, let alone to their owners,” he said. Many owners assume their interacting with each other is adequate, “but when the puppies are five or six months old and meet an unfamiliar dog in a novel setting, they absolutely freak out.”

Dunbar points out that raising littermates necessitates training two puppies—particularly challenging when they essentially wear blinders to all but each other. “It’s more than twice the work; it’s exponential. The two combine to produce levels of energy that we can barely measure. Tension develops in training and compliance as they squeeze the owner out of the relationship. They’re always living with an enormous distraction—each other.”

The Tie That Binds
Cohabitating siblings may become so emotionally dependent on each other that even short separations provoke extreme distress. Behavior specialist and author Nicole Wilde recalls a case in which two nine-year-old sibling Huskies attended her group class. “They were so bonded to each other that I literally could not take one and walk a few feet away to practice loose leash skills because the other would scream.”

Wilde believes the problems are rooted in hyper-attachment, leading to hindered social development and communication issues. “People assume that having two same-age pups that play together and interact constantly covers their dog-dog socialization needs, but they in fact don’t learn how other breeds 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, but his rude behavior might not be tolerated by a new dog in a new setting.”

During my appointment with Leslie, we determined that the best course was to re-home one of her twelve-week-old siblings. Dunbar agrees that it’s often best to separate littermates, especially if symptoms appear early, so that each has a chance to develop normally as an individual. This is obviously a burdensome decision for the overwhelmed owner to make, a sort of canine Sophie’s Choice, so he recommends that the new owner meet both puppies and determine which to take home.

Together Forever
Owners committed to raising a pair should ensure the puppies spend significant portions of every day apart so that each learns how to be alone—a key lesson in any well thought-out puppy program. This means feeding, walking and training separately, with individual crates in different parts of the home. Even trips to puppy socials and the vet should be separate so that both learn to incorporate these episodes into their psyches without being overly dependent on their littermate.

This separate-but-equal arrangement is time-consuming, exhausting and seems to defeat the original intent of acquiring siblings. Wilde notes that planned separations must begin immediately. “I’ve been called into homes where four-month-old siblings have been sleeping in the same crate for eight weeks and not purposefully separated by the owners, who had the best intentions but were unaware of littermate issues. Even getting the puppies to sleep in separate crates right next to each other is traumatic for them.”

Dunbar, too, is adamant that a key lesson for a puppy to master is how to be content with being alone, all but impossible with two siblings. “Once we’ve done that, yes, he can live with other dogs and have free run of the house. But if you don’t teach puppies early on how to be alone, and especially with siblings who have always been together, it will be catastrophic when one dies.” Dunbar encourages multiple dog households—“I always like having three dogs”—but the timing, temperament and age that each enters the home is paramount.

Most people contacting me through my blog never heard of littermate syndrome before finding the post while researching symptoms observed in their dogs. Increasingly, trainers and behavior professionals recognize that the cons of adopting siblings far outweigh the pros. “The only advantage I can think of is a short-term gain of the puppies being less lonely in the first month of life”, says Dunbar. “Everything else is a loss.”

Exceptions and Hope
While the majority of comments to my blog corroborate struggles in raising siblings—including the ongoing aggression and fighting often seen between same-gendered littermates—others write of well-adjusted cohabitating pairs. A common thread seems to be that littermates are more likely to thrive when introduced into a household with an older dog, who perhaps acts as an arbiter and stabilizing influence.

Myriad factors affect dog behavior, including genetics, early life experiences and owner engagement. As University of California/Davis veterinary behaviorist Dr. Melissa Bain points out, “two fearful littermates very well may be genetically predisposed to fear.” Bain is less inclined to apply the term syndrome to the set of symptoms: “It makes you think all littermates have problems, which is not the case.” She also emphasizes that the level of owner involvement is key, saying “the symptoms escalate when the owners treat them as one dog with eight legs.” When conflict ensues within the pair, Bain believes it’s due to the dogs being too similar in size, age and gender. “This uniformity makes it difficult for the siblings to delineate a hierarchy,” she said.

After Leslie’s second sibling had been re-homed, her remaining puppy began to thrive under a remedial socialization program. “Dora has blossomed in the last three months into a delightful household companion and she continues to improve. She now approaches people out of curiosity. We know she would still be fearful had we not separated the two before it got any worse. Dora has become more confident with all kinds of dogs and successfully completed a group obedience class.”

Increased Awareness
Recognition of the risks appears to be spreading, with many breeders and shelters declining to place siblings together. Shelley Smith, adoption center manager at Pets Unlimited in San Francisco, said her shelter stopped placing siblings together after a particularly disturbing case. “A dachshund mix named Thelma was returned to the shelter because her sibling repeatedly attacked her and she had multiple injuries by the time the heartbroken family returned her to us. Thankfully we were able to re-home Thelma, but it’s almost certain the fighting and anxiety could have been avoided had the two littermates not been placed together. We now separate siblings and inform adopters about the rationale for our policy.”

While siblings blessed with extraordinary genes and socialization-forward owners may deflect littermate syndrome, the consensus among canine professionals is that it’s not worth the risk. Most would encourage new owners to adopt a single puppy that suits their lifestyle and to focus on the training and socialization that strengthens the interspecies bond unique to humans and dogs. Once your puppy is a dog, by all means, get a second since the two will be at completely different stages, and the older one may very well emerge as a great life teacher to the younger.

Jeff is nationally-certified through the highly-respected Certification Council for Professional Dog Trainers, attaining the CPDT-KA distinction.

In addition to his CPDT-KA certification, he is a professional member of the Association of Pet Dog Trainers.


Having owned well-trained dogs all his life, He started Better Nature Dog Training to exploit decades of experience teaching across a number of fields.