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Littermate Syndrome

Written by Assistant
Assistant is passionate about all sorts of domesticated pets. They have written dozens of articles across the web.
Published on
Wednesday 23 February 2022
Last updated on
Tuesday 9 May 2023
littermate syndromes in dogs
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Littermate syndrome is a little difficult to define. It is a non-scientific term and has little to no professional research. Therefore, it is not always a common household term, nor does it have a strict definition. Broadly, it refers to behavioral problems that exist when two or more siblings grow up together after they have hit rehoming age. At the time they are 8 – 10 weeks old, some breeders and trainers believe that it is a bad idea to keep them together and especially rehome them together.

Today we will go into the suspected issues that are associated with littermate syndrome. Furthermore, we will look into causes and explanations that people believe to be true. With no confirmed studies to back up this theory though, it is still a worldwide debate that we can all agree on and needs confirming evidence. So what is littermate syndrome? Well, let’s discuss and explore it together.

What is Littermate Syndrome

Littermate syndrome is a term used to describe bad behavior that occurs when raising two siblings together after 8 – 10 weeks of age. As it is not scientific, the description varies and targets different areas of poor behavior from dog to dog. It appears to have three varied categories. Some believe that it leads to sibling aggression, separation anxiety, or general behavioral and training issues.

Some trainers and owners also know littermate syndrome as littermate/sibling aggression syndrome. Due to these puppies always being together and constantly competing, they may become possessive, aggressive, and overall jealous. It may be believed that this constant competing leads to two dogs that are overly defensive and possessive. This can occur with food, toys, people, and even external socializing. Some trainers believe that these dogs see all as competing threats sop may have a more aggressive nature.

Another problem that may arise is separation anxiety and general anxiety. Due to these two dogs always being together, when they are apart they are not very confident and even in general situations may struggle with meeting and socializing. These dogs may show aggression due to increased feelings of anxiety or may avoid social situations by hiding.

Lastly, one theory for littermate syndrome is it affects your dog’s general behavior. They may be more destructive, be more difficult to train, and some people even believe dogs raised with their siblings may have lower IQs. It is a collection of negative consequences affecting your dog’s feelings and behavior in a variety of areas.

littermate syndrome definition
This is a non-scientific anecdotal term that refers to a whole host of behavioral issues that tend to present between canine siblings.

Signs of Littermate Syndrome

There are some agreed-upon signs of littermate syndrome from those that believe in its existence. We will be explaining them below to help you form your opinion on the topic.


Whether it is trouble learning tricks or general bad behavior, disobedience is a common symptom of littermate syndrome. Owners suspect that the disobedience comes from one dog learning it from another, difficulty training the two together, or them just them feeling distracted. The level of disobedience may also not be the same in both individuals. One of the dogs may be well behaved and the other may be difficult to train and have destructive tendencies. It is suspected that individual differences may play a role in this.

High Anxiety When Separated From The Other Pup 

Separation anxiety is often assumed to be when a dog is separated from its human. However, it can be targeted at dogs as well. If your dogs are separated for whatever reason their behavior may start to change rapidly. More minor signs may be whining, pacing, or generally feeling unease. However, serious symptoms could be destructive digging or chewing, self-harm, jumping at the door, and howling continuously. One pup may feel it, sometimes both will, and it can make travel and vet visits very difficult.


Due to your dogs always sharing items or being around each other constantly, they may become more possessive of their toys or food. This can be seen through behavior on the canine aggression ladder. The more severe the behavior and frequency they are displaying them, the worse the guarding is. Some dogs may only guard food, others may target toys, and some target people. They can guard a combination of things as well, it can span across toys, people, and other things.

Social Difficulty

When you raise siblings together they may struggle with both human interaction and dogs outside of their family. With dog interactions, there are two forms this may result in. Either sibling may be very protective of one another. Therefore become aggressive meeting new dogs, or they may have anxiety and not know how to greet other dogs, so become submissive and try to avoid interaction. As for humans, there may be similar approaches as that of dogs.


General aggression can be apparent in dogs with littermate syndrome. This may be targeted at dogs, people, or even the sibling they are living with. Those that believe sibling aggression is real usually agree that aggression is one of the primary symptoms. Your dog may show this through more minor behaviors like growling or whale eyeing. However, from a young age, these dogs may snap, bite, and bare their teeth regularly in a lot of different situations. This is one of the most worrying signs.

What To Do When This Happens

There are a few pieces of advice we can offer if you believe littermate syndrome may be affecting your dog. However, remember that a behaviorist or trainer may be beneficial for more severe behaviors.

littermate syndrome cure
In some cases, avoidance of this issue is the best solution.

Gradually Separate Your Dogs

Your dogs may be able to feel calmer and less defensive if you keep them separate in certain situations. They will be able to develop confidence and understand proper socialization techniques through trying alone. Use very gradual methods to separate them, and do not feel they always need to be separate. Allow them to sleep separately in their own crates, give them one-on-one play sessions in different rooms, also allow them to eat by themselves. If you can, consider taking them to different behavioral classes or walking them separately sometimes. It helps to break the toxic pattern that can lead to poor behavior.

Socialize Them Each With Other Dogs

While walking them or in socialization classes, ensure they are alone sometimes. Allow them to not feel defensive, jealous, or any other negative behaviors from having their sibling alongside them there. If they already have issues, consult a behaviorist first for help and then progress to a socializing class. This is a safe area where dogs can get to know one another and become more comfortable with greeting each other. Your dogs can learn these techniques alone and then demonstrate them together in the future.

Allow Time Together

The bond your dogs have formed is still so important to maintain if they are living together permanently. Make sure to give yourself time to allow your dogs to bond. Play sessions, some walks together, and letting them have naps together. It will help them to maintain their bond whilst still allowing them to have their own personality, time to themselves, and self-confidence. A trainer or behaviorist can help maintain sessions between your dogs to ensure they are all healthy and there is no danger of aggression or encouraging bad behavior.

Littermate Syndrome: FAQ

We have some more answers about littermate syndrome to help you understand all you need to about it. Have a look at our FAQs below.

How do you correct littermate syndrome?

Remain calm, give your dogs space from one another, and use positive reinforcement are our top tips. A behaviorist and obedience class with a trainer can also be hugely beneficial in aiding your dogs. Punishing them may actually make their behavior worse, so always work with gentle training methods and rewards for them being good.

Should littermates sleep together?

We advise having separate sleeping areas for littermates. This can firstly help to minimize separation anxiety and allow them to have confidence in themselves. They can nap together during the day but at night we advise crate training and even having them in separate rooms if possible. By crate training them to their own crate, you should be able to easily encourage them to go to bed in their own crates. If possible, do it during their younger years so they do not struggle at an older age wondering where to sleep or why you need to separate them.

How long should you wait before getting a second puppy?

Behaviorists often advise waiting a year before getting another puppy. This gives your first dog time to become comfortable with their home, family, and begin training and learning. They can have a firm grasp of proper training and socialization and also have confidence in being by themselves. Then, when you get your new puppy, you know you already have one well-behaved dog.

Are dogs happier in pairs?

Dogs are social creatures, however, they do not necessarily need to live in pairs. If they are able to get playdates and meet other dogs on walks then they are okay living alone. Sometimes, dogs prefer to live in single dog households and many do so well. If you are interested in getting a second dog, know that they do not need it unless their social needs are not being met. They should also be addressed directly as opposed to getting a second dog.

How do you introduce a second dog?

Gradual introductions with patience are the key to introducing another dog. Do so in a neutral place and be sure to be able to remove a dog if there are any negative signs of behavior. Initially do short introductions and increase them until both dogs are comfortable. If you have concerns about the dogs meet, start off by letting them smell blankets the other has used. Allow them to get used to each other’s scent before providing an introduction.

Littermate syndrome has not been confirmed to be true. It is still highly debated by owners and behaviorists. If it is a real syndrome, then it can help to explain some negative behaviors that may occur when owning siblings. Understanding the behaviors that arise and why you can then help to make your dogs feel better. Contact a behaviorist for support if you have any worries or if your dogs are showing signs of aggression. Do you believe in littermate syndrome? Let us know in the comments!

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