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Littermate Syndrome: Symptoms of Littermate Aggression + Prevention & Training Tips

Updated: Oct 19, 2021

The companionship, newfound love, and respect from a dog are worth their weight in gold. The adoring eyes, yipping, licking, and loving attention - these are the things we all get excited about when we know that we’re getting a new puppy. Yet one dog, it seems, is never enough.


If you were already going to bring one fur baby home, is there a good reason not to consider bringing another one as well? They’re small, right? And they get along so well with their brothers and sisters.



You might want to reconsider though. There’s a little something called Littermate Syndrome that could be a huge problem for you and your two puppies.


What is "Littermate Syndrome" (LS) and is it real or a myth?


Littermate Syndrome (also known as Littermate Aggression or Sibling Aggression) is a series of behavioral issues that arise when two or more puppies from the same litter/same age are raised together.


After about eight to ten weeks, a puppy is ready to start its journey to adulthood. A puppy will need time and patience to discover who it is as a dog. If a puppy has to share your attention (or is made to feel the need to share it) with its sibling, this could be hazardous to its health and mental wellbeing.


We should state that there is no conclusive, scientific proof of Littermate Syndrome, but owners have shared story after story about their experiences of adopting two dogs at once - how what they thought would be a great idea backfired.


Still, the idea that Littermate Syndrome is a myth persists.


What are the symptoms of littermate syndrome? Will your dogs fight?


While it might seem like a swell idea at first, our recommendation is that you don’t get two puppies from the same litter. There are a plethora of issues that could plague your household for years if they are not addressed immediately. Let’s review the most common symptoms of littermate syndrome.


  • Hyperattachment

Imagine what it would be like if you couldn’t be with someone you craved. This is a possible issue with LS. If the puppies feel lost without their other half, they could become combative with other dogs or humans, including their owner. They could have an unhealthy, obsessive need to spend every second of every day with their siblings.

  • Aggression

You have probably seen the tiniest of pups pouncing and playing around. They love jumping on top of each other, politely gnawing at each other’s ears and feet. After a few months though, this same jokey attitude could be misconstrued as an attack. Sibling rivalry isn’t the most common tell-tale sign of LS, but it is certainly a possibility.

  • Fear

There's a technical term for this issue – neophobia. As defined by Oxford Languages, neophobia is an “extreme or irrational fear or dislike of anything new or unfamiliar.” To a new puppy, everything is new or unfamiliar. The only thing that is a known quantity is their sibling; if they are always with their siblings, they could grow to fear everything else.

  • Anxiety

Do you remember what it was like being apart from your mother and father when you were young? Maybe a brother or a sister? You probably thought they’d never come back. With LS, this is a real issue between two siblings that could last their entire lives. If not addressed, the puppies could howl or cry the entire time they are separated from their siblings.

  • Lack of Social Skills

Remember we spoke about neophobia? Your expectation might be to take your pup to play in the park. While they know each other’s barks and scents, the aromas and sounds of potential new friends could set them off. They don’t know how to respond to new dogs. They could become pugnacious – pun intended.

  • Training Issues

Consider this scenario: You’ve brought two puppies home to share your house, your family, and your heart. But they have each other, why would they need to listen to you? The simplest of obedience training could be undermined by a lack of need for anyone but each other.


Let’s be clear. While there are pairs of dogs from the same litter that get along beautifully and have no behavioral or socialization issues whatsoever, why risk it? Do what’s best for your new best friend.


We here at Jenna Lee Designer Doodles have our Exclusive Puppy Matchmaking System. We want to assist you in avoiding all of the issues that we’ve outlined above. Our multi-tiered system takes the guesswork out of opening your home to the cuddliest of cuddlers.




Could Littermate Syndrome occur between two dogs that aren’t from the same litter?



While LS is most common between two dogs with the same lineage, similar issues can occur with any puppies who are around the same age.



Can you prevent Littermate Syndrome with training or treatment?


You might be reading this blog at a time when decisions have been made and you already own two puppies. Is it too late to avoid LS issues? Here are a few pointers:

  • Training to prevent LS

We have a wonderful training program for new puppies through JLDD, but you might be in a position where you need to look into other training options.


Training two puppies of different breeds and ages together could be a real challenge, especially if they’re from the same litter. Your new friends will need to be trained separately.

The trick here is that you will want to train them at the same time but in two different places. Dogs are hierarchical animals who, for the most part, respect the alpha and beta pecking order. One puppy should never feel like the other is more important.


If they see each other during training sessions, they could pick up on each other's bad habits or, worse, not pay any attention to you at all. This takes time and probably a lot of patience. Just like children, puppies need time to develop their own personalities and good habits. They do so best with positive reinforcement.

  • Separation

In this case, when your pups tell you they need a little space, it’s a good thing. They don’t need space from you but from each other. You don’t want to rip the two apart from each other right away because that could do more harm than good. Slow and steady wins the race.


If you only have one crate, a second will be required. This also goes for toys and food bowls; the entire gamut. When you put them in their respective crates, make sure they’re right next to each other. They can hear and smell each other but won’t be able to directly interact. This should be done for short periods – about 45 or so minutes at a time.


Over time, you can move the crates farther and farther apart. This will do two things. It will allow the two to become independent since they have their own space. And it will also allow them to get excited to be reunited with one another without fear of codependency.

These same rules would apply to bedtimes: two separate crates, two separate spaces.

  • Rehoming

We hope this is the last resort that you'll never have to consider. Puppies become part of your family, and you want to give them their forever home. But dogs are pack animals, and you want to make sure that your family is safe, including your adorable and furry fops. If the puppies choose one another over someone else in your house and grow aggressive, any aggression shouldn’t be overlooked or taken lightly.


If you can’t seem to get over the hurdles of taking care of two littermates, then you probably want to contemplate moving one of them somewhere else. You could then work with their new family to make sure that both puppies are the happiest individuals they can be moving forward. We know you want to keep your family together, but safety first.



If you’re thinking about two dogs instead of one, be on the lookout for Litter Syndrome symptoms


Our recommendation, again, is NOT to get two puppies at the same time. It’s exponentially more difficult and could hurt them and yourself far more in the long run.


If you already have one guardian angel covered in fluff in your home who is at least 1 year old and you want to bring in a second, consider one of our wonderful doodle doggies, born and bred in South Carolina.


Doodles have the most spectacular, familial and fun-loving personalities. Check out our other blogs or, if you’re ready today, fill out one of our applications and start the process!


Jenna and the JLDD Team


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