Skip to main content

What is littermate syndrome? Why this puppy bond can be a problem

Why you want to avoid littermate syndrome (and what to do if you didn't)

Golden retriever puppies
Chevanon Photography / Pexels

What’s better than bringing one puppy home? Two — or so you might think. Welcoming two puppies at the same time can seem adorable in theory, especially if they’re from the same litter. The two puppies already knew one another and were perhaps born within seconds of one another. Siblings growing up together, what could be more fun?

However, most animal behavioral experts recommend against getting two puppies on the same day (or within six months). They’re not trying to rain on your puppy parade. Instead, experts warn against the possibility of littermate syndrome. What is littermate syndrome, and why can it be so stressful? Let’s discuss. We’ll also work through ways to treat littermate syndrome if your pets already have the issue.

What is littermate syndrome?

Three young puppies on grass
Mateja Lemic / Pexels

Littermate syndrome is a set of behavioral issues that are most common in pets of the same litter. However, the problem can arise in pets that are close in age and from separate litters. Littermate syndrome occurs when two puppies are too closely bonded.

While two puppies who love one another so much sounds sweet, littermate syndrome can have a ripple effect, causing more unhealthy behaviors that aren’t good for pets (or people), like anxiety and fear. When puppies are raised together right after weaning, they can form such a tight-knit bond that they can’t stand separation.

This connection develops during the crucial puppy socialization period of 3 to 12 weeks. During this phase, puppies start the weaning process. As they become more independent from their mothers, they get to know the species that will become a source of lifelong companionship: humans. During this time, they start to learn what causes positive and negative reactions. A nuzzle against a leg may earn a dog a good ear scratch. Chewing a throw pillow? Not so much.

Pets with littermate syndrome don’t look to humans for validation and affection. Instead, they look to one another. In other words, they have developed a co-dependence. Unfortunately, this inclination can lead puppies to feed off each other’s fear responses to new stimuli (and everything is new when you bring a puppy home). Additionally, puppies won’t always be together, even in the same home. You may need to take one to the vet or want special time with a puppy. Dogs with littermate syndrome can display even more negative behaviors when separated.

Symptoms of littermate syndrome include:

  • Separation anxiety
  • Fear of anything new (people, objects, animals, or experiences)
  • Fear-based aggression, like barking or biting, prompted by perceived threats
  • Leash reactivity
  • Increased fighting at 6 months old when sexual maturity is reached
  • Timid behavior in the more submissive puppy

These symptoms sometimes appear after some time. Littermate syndrome can first present at 6 months old.

What to do about littermate syndrome

Two huskies play fighting
Mihaela Pastiu / Pexels

Littermate syndrome can be a massive hurdle to overcome and is a long process. Pet parents will have to work with each dog separately and together, and professional help is likely needed.

Prevent littermate syndrome

Your best bet is to avoid littermate syndrome in the first place. Save yourself the trouble by resisting the (valid) urge to take in two puppies simultaneously or within six months of one another. Socialize the new puppy by bringing them to meet new people and other animals. Sign the puppy up for obedience training classes so they can learn basic commands.

Then, once that six-month mark has come and gone, ask yourself if you still feel up for having another puppy in the home. If your answer is a resounding yes, bring your current pet for meet and greets with prospective puppies and choose one you both love. Speaking with a breeder or member of the shelter staff about your current pet’s age and behaviors can also help ensure now is the right time for (another) new puppy.

Crate training

From the get-go, ensure dogs have separate crates. Avoid crating dogs together — this tactic only exacerbates the strong but unhealthy connection involved in littermate syndrome. You can keep the crates next to one another at first. However, gradually move them further apart as time passes so your pets get used to having more personal space.


Train the dogs out of sight of one another to build separate human-canine bonds with each pup. You want the dog to look to you — not their canine companion — for assurance and commands. Training should also include separate socialization. Bring each pet around new stimuli, like the park, separately.

Once you feel separate training sessions and park trips are consistently going well, you can phase back in together times. For instance, bring pets to the park, but ensure each one has their own human. Spend time walking in opposite directions. Watch their reactions. Are they stressed? OK? That’ll help you gauge how they’re healing from littermate syndrome.

Final thoughts on littermate syndrome

A picture of two Biewer terriers puppies playing tug of war with a rope toy
Amalia33 / Pexels

Two dogs with an unbreakable bond can sound amazing. However, littermate syndrome is anything but. Littermate syndrome is a behavior that prompts two dogs from the same litter or close in age to become co-dependent. They look to one another for assurance, which can actually cause fear and anxiety.

Aggression and separation anxiety are common in dogs with littermate syndrome. Your best bet is to avoid littermate syndrome by not bringing home two puppies at once. Instead, wait six months (at least). If your pets have littermate syndrome, working with a trainer to get your dogs used to life without one another (even if you plan to keep both) can be life-changing for everyone.

Editors' Recommendations

BethAnn Mayer
Beth Ann's work has appeared on and In her spare time, you can find her running (either marathons…
These are the longest-living dog breeds
These pups stick around longer than any others
Purebred Chihuahua puppy and a Great Dane sniffing each other

Everything would be better if dogs lived longer. We want our pets to stay with us forever, but sadly, these guys only stick around for a decade or two, at the most. Still, longevity in all pets depends heavily on a few factors, including breed, size, genetics, and, of course, how well you take care of her.

Knowing in advance which pups live the longest can help you choose the right one for your family and manage your specific animal's health conditions. We'll cover the longest-living dog breeds and how to best keep your dog happy and healthy for as long as possible.
How long do dogs live?

Read more
5 reasons you really need to get a dog car seat
Safety first: Why you'll want to invest in a dog car seat (or similar product)
A French bulldog in front of car

The image of a dog with their head out the window — tongue out and ears blowing in the breeze — is classic. Whether they're getting an unpleasant surprise (a vet appointment) or joining their pet parent on a visit to the park or cross-country road trip, the dog is happy in the moment. Is the precious cargo safe, though?

Not to scare or shame you, but no. The best way to keep your beloved pet safe is in a dog car seat or similar product. The idea may seem like helicopter pet parenting. However, for several reasons, you'll want to strongly consider a dog car seat or another product that keeps the dog safe and secure en route to a destination.
Why you'll want to invest in a dog car seat

Read more
How many dog breeds are there, really?
Knowing about your dog's breed can help in their care
A woman outside sits with a pack of dogs

It frequently amazes humans how much our dogs seem to understand and respond to us. Some part of this likely lies in the distant past when dogs chose us to be their companions. But a lot of it stems from selective breeding that has taken place over thousands of years.

More recently, our pets fall so neatly into different breeds because we chose specific characteristics that exist across a specific type of dog. For example, you'll recognize the coat and stature of a German shepherd from 100 feet away and likely instantly identify the yap of a Chihuahua without even seeing them. The question is then, how many dog breeds are there? We'll take you through the details.
What is a purebred dog?

Read more