Littermate Syndrome in Dogs: Is It Real or Made Up?

Littermate syndrome is thought to occur when canine siblings are raised together, but the topic is controversial.

Published February 25, 2023
Puppies at wooden box

Littermate syndrome is a term used to describe abnormal and unwanted behavior of some littermates who are raised together. It is also controversial. Some dog experts believe littermate syndrome is a myth, and others argue it is a real condition. Although the topic is disputed, littermate syndrome is thought to occur when two or more puppies from the same litter go to the same forever home, resulting in the puppies being so bonded they struggle to form normal relationships. It is critical to understand the theory of littermate syndrome as well as how to prevent it from occurring.

What Is Littermate Syndrome in Dogs?

Littermate syndrome is thought to occur when littermates who live together form an overly strong bond. Littermate syndrome can lead to a variety of problems, especially if the puppies don't receive proper socialization.

Understand that the term "littermate syndrome" is not a medical diagnosis a veterinarian will make. Some canine behaviorists use the term to refer to a set of behaviors that littermates raise together can display. However, there is no consensus about what these behaviors are exactly.

Anecdotal reports of littermate syndrome describe it as something like canine codependency between littermates. It is characterized as neurotic behavior, aggressive behavior between siblings, or more generally as an inability to form normal social bonds with other dogs or people.

Fast Fact

There are no scientific studies either supporting or disproving the existence of littermate syndrome, but some canine behaviorists recommend against getting puppies from the same litter as a precaution.

Signs of Littermate Syndrome

One of the most commonly reported signs of littermate syndrome is that your dog will become very attached to their littermate, suffering from separation anxiety and displaying negative - even neurotic - behavior. In some cases, this can lead to aggressive behavior toward humans because dogs are trying to protect their littermate.

You may also notice that your dog becomes very protective of their littermate and tries to keep them away from other people or animals. Alternatively, dogs with littermate syndrome might show aggression toward one another, more than non-siblings would. If you have multiple dogs who are not related and they are displaying these signs, the behavior is probably not caused by littermate syndrome, but instead by social isolation or boredom.

Dogs with littermate syndrome may:

  • Display separation anxiety when away from their littermate.
  • Show excessively aggressive behavior toward each other.
  • Guard their littermate or become aggressive toward other animals and people.
  • Appear anxious or nervous about normal social interactions, or in general.
  • Have difficulty with obedience training or even house training.

Preventing Littermate Syndrome

The biggest risk of littermate syndrome is that if two or more littermates are not properly socialized, they may develop these negative behaviors. This can make it difficult for them to integrate into new families with other pets and children, or spend time away from each other out in public.

Socialization is absolutely essential for puppies. For dogs who might have littermate syndrome, it is 10 times more important. If you have littermates and you suspect they might be developing behavioral problems, it's essential that you make socialization a daily priority. This will help prevent littermate syndrome in the future. Also, consult with a canine behaviorist for guidance if you think your puppies are showing any syptoms of littermate syndrome.

Socializing Puppies to Prevent Littermate Syndrome

A surefire way to help your puppies avoid littermate syndrome is to expose them to as many different people and animals as possible. This can be done with everyday activities, like taking them on walks around the neighborhood or visiting friends' houses.

Another strategy is to take them to obedience classes, where they will meet new dogs and other people, but you must make sure that the class has a good teacher who knows how to handle puppies!

The best way to avoid littermate syndrome is to start training before symptoms show up. If your dogs already display this behavior, you need to build a training regime based on positive reinforcement. Start by training your dogs separately, and as their behavior improves, begin holding sessions with them together. Regular training and socialization can include:

  • Crate training your puppies in separate kennels or crates.
  • Providing high levels of daily socialization through walks, visits with friends, and trips outside the house.
  • Positive training activities with the littermates separated.
  • Trips outside the home, one dog at a time.
  • Making sure both dogs receive ample amounts of stimulation and exercise.
  • Obedience sessions with both dogs present, preferably with multiple handlers at first.

This list only scratches the surface of what's possible in training to reduce littermate syndrome. if you have dogs who display syptoms of this condition, talk to a canine behaviorist and build a comprehensive training plan to overcome your dogs' behavioral problems.

Why Some Believe Littermate Syndrome is a Myth

There are several reasons some canine professionals believe littermate syndrome is a myth. These reasons include the following:

  • There's no empirical scientific evidence for littermate syndrome. The only evidence is anecdotal.
  • There's no consensus among veterinarians or canine behaviorists about whether the condition is real.
  • Some sources claim unnamed guide dog organizations specifically studied littermate syndrome - and this may be true - but there is no published, peer-reviewed research confirming this study.
  • The behaviors attributed to littermate syndrome are inconsistent. Other factors could contribute to siblings having a strong bond, including the amount of time spent together.
  • Other biological or behavioral problems could be the cause of aggression or anxiety in dogs thought to have this condition.
  • The signs of littermate syndrome are very similar to separation anxiety, so it's difficult to tell which condition is at fault.

Avoiding Littermate Syndrome

Whether the theory of "littermate syndrome" is factual or a myth, there is evidence that dogs living in the same home can become more bonded to one another than to other dogs. While this generally isn't a problem, you should still begin socializing your puppies as early as possible. This will help them become more comfortable around new people, in new places, and near other dogs as they grow up. By exposing your puppies to a variety of situations and stimuli, you can avoid future behavioral issues due to over-familiarity with one another.

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Littermate Syndrome in Dogs: Is It Real or Made Up?