Littermate Syndrome in Dogs: Symptoms and Management

Six Minutes
Jun 27, 2023

Puppy siblings raised together can easily become codependent with one another. These codependent behaviors can be referred to as littermate syndrome. Dogs raised together who aren’t from the same litter can also develop similar symptoms.

It’s undeniable that some pups can exhibit specific behaviors when they’re thick as thieves with another. So let’s dive into what littermate syndrome is, some behaviors to watch out for, and advice for managing those behaviors.

What Is Littermate Syndrome?

Littermate syndrome, which is sometimes referred to as LMS, describes the behavior of two bonded dogs that develop codependency and don’t go through social development properly.1 There’s no scientific evidence for this syndrome, rather it’s based on anecdotal evidence. Behaviors vary in each pair and can range from aggression to separation anxiety between the two dogs.

Dogs with littermate syndrome generally have poor socialization skills with other dogs and can be fearful or aggressive.1 This is because they’ve likely not figured out how to interact with other dogs or humans without their littermate right by their side for support.

How Common Is Littermate Syndrome?

While most dogs exhibiting symptoms of littermate syndrome are siblings adopted from the same litter, two unrelated puppies who were raised together can also develop it. Any two puppies adopted and raised together — or within 6 months of each other — may be at risk for developing these behaviors.2

A few dog breeds, such as terriers, dachshunds, border collies, and shepherds, may be considered higher risk for developing littermate syndrome.3 However, this is based on anecdotal evidence, not scientific fact.

At What Age Does Littermate Syndrome Start?

A puppy’s first 12 weeks — called their socialization window — are crucial to their social development.4 Dogs that haven't experienced new situations, places, people, or animals during this time may be fearful or otherwise avoidant in the future.

If your puppies went through the entire socialization process joined at the hip, they’ve likely learned to rely on each other and may have difficulty in new situations by themselves. They’ve also potentially established any aggression or attachment between them as normal behavior.

Can littermate syndrome be cured?

Since littermate syndrome is a set of behaviors, not a scientifically proven condition, there’s technically no cure. Rather, you can treat or manage the behavior in each dog individually, consulting your vet and a dog trainer for support.

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Littermate Syndrome Symptoms

Littermate syndrome can look different in every pair of dogs. But there are a few behaviors that hyper-attached dogs can commonly exhibit:1,2,3

  • Separation anxiety when apart from each other
  • Protectiveness of one another
  • Aggression with one another
  • Resource guarding (aka food or toy aggression)
  • Anxiety in everyday situations
  • Difficulty focusing on training

How To Manage Littermate Syndrome

Typically grown dogs can spend lots of time together. However, if you have dogs in your household displaying some of these behaviors, it’s important that littermates (or any puppies) experience situations independently to properly develop. Here are four things you can do, whether managing grown littermates or training new pups.

Train individually

Each dog needs one-on-one time with you. Consider teaching them their training cues, taking them for car rides, and playing with them one at a time. While this can be more work, it can be a good way to ensure they develop into independent adult dogs or boost their confidence levels if they’re already grown.3

Provide separate spaces

Consider putting your puppies’ beds or crates in different rooms to provide time apart. You may have to slowly adjust to this if your dogs are grown, especially if they’re already anxious when apart for too long. To protect against resource guarding, provide your dogs with their own food and water bowls, ideally in separate areas as well.3

Prioritize socialization

Expose your puppies to as many situations and spaces as possible during their socialization window. Introduce them to different people and animals while they’re young so they’re comfortable later on. Make sure you do this individually, so one pup can’t depend on the other during the process. And, if you have grown dogs, start by addressing any separation anxiety before you spend ample time with them apart.3

See a dog trainer

Littermate syndrome can be dangerous, especially if your dogs are on the aggressive end of the spectrum and tend to fight with each other. You’ll want to prevent bite wounds, injured paws, and any other injuries from happening. While not as dangerous, separation anxiety and difficulty training can also be detrimental to a dog’s health.

Whether you’re seeing concerning behavior early on or have two bonded adult dogs you’re working with, a dog trainer or behaviorist can help. They’ll identify major concerns, manage aggression, and work with each dog independently to mitigate risks.

How To Prevent Littermate Syndrome

Ultimately, preventing littermate syndrome can be done by not adopting and raising multiple puppies around the same time — whether from the same litter or not. Dog trainers may recommend getting one dog at a time and not getting another until the first is past their socialization window.

But if your mind's made up on adopting two or more together, consider socializing, training, and bonding with one dog at a time. This way they’re getting your full attention, navigating new situations alone to develop confidence, and not becoming dependent on another dog.

Consider Insuring Your Pups To Help With Vet Bills

Littermate syndrome can cause problems. It could result in pups getting into a scuffle, resource guarding, or exhibiting other aggressive behaviors. Dog insurance may help cover the cost of injuries from housemates or littermates being aggressive. It could also cover anxiety medications like trazodone.

In addition to individual plans, MetLife Pet offers multi-pet policies where up to three dogs can be covered on one plan. This can help you with the costs of managing behaviors and medications if needed. Start your journey today by getting a free quote and protecting your pups for the future!

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Healthy and Happy

**As with any insurance policy, coverage may vary. Review our coverage and exclusions.

1 “Littermate Syndrome in Dogs,” The Spruce Pets


3 “Guide To Littermate Syndrome In Dogs: Everything You Need To Know,” Pupford

4 “Social Behavior of Dogs,” Merck Veterinary Manual

Coverage issued by Metropolitan General Insurance Company (“MetGen”), a Rhode Island insurance company, headquartered at 700 Quaker Lane, Warwick, RI 02886, and Independence American Insurance Company (“IAIC”), a Delaware insurance company, headquartered at 11333 N Scottsdale Rd, Ste 160, Scottsdale, AZ 85454. Coverage subject to restrictions, exclusions and limitations and application is subject to underwriting. See policy or contact MetLife Pet Insurance Solutions LLC (“MetLife Pet”) for details. MetLife Pet is the policy administrator. It may operate under an alternate or fictitious name in certain jurisdictions, including MetLife Pet Insurance Services LLC (New York and Minnesota) and MetLife Pet Insurance Solutions Agency LLC (Illinois).

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