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📸 by Xalion Malik

The essentials

  • Littermate syndrome can lead to behavioral issues in sibling dogs — Separation anxiety and aggression are common examples of how it can impact dog behavior.
  • Experts disagree — Some pet professionals argue against using the term because of its lack of research-based evidence.
  • The prevailing wisdom is that littermate syndrome is real. If you want to have multiple dogs, it’s best to wait until one is an adult before bringing home a new furry friend.
  • It is possible to have well-adjusted littermates — Dogs are individuals and each deals with life experiences differently. There are training methods to help dogs cope with littermate syndrome.

What is littermate syndrome?

The term ‘littermate syndrome’ refers to behavioral issues that arise when two or more sibling puppies are raised together. Potential issues include separation anxiety, neophobia (fear of the unfamiliar), and aggression. Littermate syndrome affects dogs over 8-10 weeks of age, which is typically when young puppies join their forever homes.

Dachshunds, Terriers, Border Collies, and Shepherds are often cited as having a high propensity for littermate syndrome, but there is no clear scientific evidence that certain breeds experience littermate syndrome more or less than other breeds. Doggie psychology and brain chemistry, much like our own, is complicated. Each dog is an individual with their own experiences and quirks which shape how they regard and cope with the world around them. Breed might have some influence on this, but it shouldn’t be a factor in considering whether or not to adopt two siblings of a certain breed.

Not every pair of dog siblings will experience littermate syndrome, but there is no way for a potential pet owner to know that. This is why the general advice is simply not to adopt two dogs from the same litter. However, each dog is different, as is each pair of dogs.

In some cases, sibling dogs may have bonded in a way where it makes sense for them to be raised together. Dog adoption of any kind is a very big and complicated undertaking that is better handled on a situation-by-situation basis. Adopting any pair of dogs must be done so with as much care, thought, and preparation as possible. If you do or already have adopted dogs from the same litter, you must be prepared to put in extra time and training so your dogs live their best lives. We’ll discuss how to do this a little further down.

3 early signs of littermate syndrome

Dogs continue to bond with each other rather than with anyone else when you bring two puppies home. Because they are only comfortable with one another, they can become neophobic or fearful of anything new. If the dogs become nervous around new people, things, or situations, this could be a sign of neophobia due to littermate syndrome.

Separation anxiety. Another indicator to watch for is separation anxiety, especially in situations where the dogs are apart for just a short period of time. Dogs experiencing separation anxiety will whine, cry, howl, and be otherwise anxious. What’s going on here is that the dogs are so attached to one another that they cannot stand being apart. This is an unhealthy way to be for any dog, as it causes them undue stress and emotional turmoil. Another related sad outcome to this is that when one of the sibling dogs dies, the other cannot cope and lives out the rest of their days in torment.

Dog training issues. Difficulty in basic obedience training is another potential sign of littermate syndrome. Potty training one dog is not easy. Two is harder, but two whose focus is only on their sibling is way worse. The dogs will be inclined to ignore you and will be resistant to training because of that.

Aggression. Aggressive behavior is another sign. Dog siblings may play rougher with one another, and this can cause severe injuries. Often, when an owner cannot address the aggression with their two dogs, they will be forced to rehome one of the dogs. This is difficult for the dogs as well as the mental health of the owner who has to make arguably a lose-lose decision.

Awareness about littermate syndrome

Like we stated before, many dog people have never heard of littermate syndrome. Speaking from personal experience, I am not precisely a spring chicken and I have had dogs my entire life, but I was unaware of littermate syndrome until last year. I just happened to overhear a random conversation while volunteering at a pet rescue.

Speaking of rescues, many shelters will not even allow two puppies to be adopted at the same time — even if they’re from different litters. Some breeders feel the same way. You will also find some people, some of whom are dog-related professionals, who do not believe littermate syndrome is real at all. Others object to the wording of the term, specifically the use of the word ‘syndrome.’ One of their objections is that new owners with sibling dogs will jump to the re-homing solution too quickly. ‘Syndrome’ is a scary word, so it’s important to understand what the littermate syndrome can mean and what can be done about it.

What does science have to say?

There hasn’t been any single conclusive research study that proves whether or not littermate syndrome is an actual medical diagnosis. However, it is a term widely accepted to refer to lots of behaviors that pet scientists have observed over many years. It’s not a conspiracy theory against puppies, but an accepted phenomenon observed and treated by professionals. Keep in mind that when there is no hard science to back up a theory, it is best to look at all sides of the conversation to best make a decision.

Also, dog psychology is constantly studied by dog behaviorists who trace the dog’s evolutionary history back to their wolf ancestors. In understanding how humans helped ancient wolves become dogs (over a long period of time; don’t adopt a modern wolf) we then can understand their relationships with one another and to us.

Because we train our dogs, it’s important to understand how training works and why. This is especially true when considering adopting two puppies from the same litter. A happy dog is a confident, well-trained dog. Littermate syndrome will make training harder. The result is less happy pooches.

👉 For more on the canine-human bond, here’s more about how dogs came to be our best friends.

Because this article is quite literally about littermate syndrome, we are focusing on the downsides of adopting sibling puppies. However, some dog owners have raised multiple pairs of siblings without incident. It is possible. We even took to Reddit to see what life anecdotes were out there. One user named No_Gains is the parent of two-year-old Alaskan malamute littermates Urs and Fenrir. No_Gains said they had no issue outside of rougher play. Other Redditors reported multiple issues with sibling puppies.

👉 Browse the entire Reddit thread

Sad dog

Separation anxiety and general fearfulness can take a serious toll on your dog's mental health

The risks of adopting sibling puppies

If you are determined to adopt canine siblings, you must be aware of the risks. That’s the best way to be prepared to help your dogs overcome the issues they’ll face. Here’s what can happen with pups who are siblings.

  • Hyper-attachment. They stick to each other like glue. If you try to separate them, you’re the bad guy and they are the miserable guys.
  • Inter-dog aggression. Playtime gets rough and they’ll hurt one another. In some cases, they are not playing but actually fighting.
  • Depression due to mourning. When the first of the pair dies, the other will not know how to cope.
  • Jealousy. If one of the pair senses the other is getting more attention, the dog may become aggressive to their sibling or to you.
  • Fearfulness a.k.a. neophobia. Because the dog has learned to only be comfortable with their sibling, anything else becomes unsafe in their mind.
  • Separation anxiety. Being away from the other dog causes extreme anxiety. Anxiety can lead to other problematic behaviors like aggression or property destruction. (Learn more about the four causes of dog anxiety.)

Here's what to do if you've already adopted a pair of littermates

What to do if you’ve already adopted a pair of littermates

The point of this article is to spread awareness about littermate syndrome AND to help dog owners who already have two dogs from the same litter. Also, in some cases, two dogs from the same litter may turn out OK. Since you’re on this site, we know you love your pets, and we are here to help you be prepared for anything!

The first thing to do is to put training first. With two dogs, it’s better to train each one separately. This alone will help each dog cope with being alone without their sibling. It also makes training easier. Just try to teach two puppies to sit at the same time. We’ll wait.

In the meantime, we have a couple of guides that can help make the training processes easy.

👉 For info specific to housetraining, here’s our handy step-by-step guide.

👉 Crating/kennel training is super important to raising a well-adjusted dog (or dogs), and we’ve got you covered on that.

Some pet owners may find that formal training classes are required. However, each dog will need to be trained separately. Essentially, the more you get each dog comfortable with being alone, the better. Also, start as early as possible — day one if possible. This includes taking your dogs on separate walks and having them sleep in separate crates. However, it is also important to understand that dogs’ wheels are always turning. They have perceived hierarchies in their brains. So, if you take one dog out first, the other may think the first dog is being treated preferentially. This can result in behavioural issues. Your good intentions could backfire. You must be attentive to your dogs’ reactions.

Regarding meal times, experts suggest individual food bowls. If you have other family members who can help, have each dog do separate things with each person in your household. Basically, you are teaching your dogs how to be OK without their sibling who they have a natural and deep bond with. Confidence can be taught — and is key to a happy pupper.

Is the third dog the charm?

Some dog owners note that having a third, older dog helps limit littermate syndrome in the two new puppies. The idea is that the pre-existing dog limits the two new puppies from bonding solely with each other. There’s no scientific research to back this up, however, it’s a common anecdote.

When to consider rehoming one of your puppies

The most common reason why people rehome a dog is for safety reasons. If two sibling dogs play or fight too hard, it can lead to severe injury or death. Giving your dog a new home is the last resort, but never hesitate to consult with a vet or a professional pet behaviorist if your dogs are too aggressive or have issues with social development.

Remember that two dogs can be a pack. A pack mentality can lead to aggression against other dogs or to people. Aggression should never be taken lightly or overlooked. An aggressive dog is not a happy dog — and dogs deserve to be happy.