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Two puppies cuddling

The essentials

  • Littermate syndrome can lead to behavioral issues in sibling dogs — Separation anxiety and aggression are examples of how littermate syndrome can impact dog behavior.
  • Use caution when adopting sibling puppies — If you want multiple dogs, it’s often a good idea to wait until one is an adult before bringing home a new furry friend.
  • It is possible to have well-adjusted littermates — Dogs have individual personalities, and each deals with life experiences differently. There are training methods to help dogs cope with littermate syndrome.

Some human sibling rivalries are fierce. Other siblings are two peas in a pod who can’t stand to be apart. Young dogs can be the same way. It sounds cute, but many pet experts say littermate syndrome can lead to destructive behavioral issues. Others argue against using the term because of a lack of scientific evidence.

The idea of littermate syndrome may have you rethinking adopting puppies from the same litter. Or, perhaps you already did and are now concerned about littermate syndrome. Here’s what to know.

What is littermate syndrome?

Littermate syndrome refers to behavioral issues that sometimes arise when two or more sibling puppies are raised together. Why is littermate syndrome bad? According to pet experts, it causes aggression in breeds not normally susceptible to destructive behaviors. Potential issues include separation anxiety, neophobia (fear of the unfamiliar), and aggression. Littermate syndrome affects dogs over 8-10 weeks of age, the point when young puppies typically join their forever homes.

Impact of breed on littermate syndrome

There is no clear scientific evidence that certain breeds experience littermate syndrome more or less than others. Anecdotally, many people think certain breeds and breed families have a high propensity for littermate syndrome — dachshunds and border collies, as well as terrier and shepherd breeds specifically.

Each dog has experiences and quirks which shape how they regard and cope with the world around them. While breed might have some influence, it shouldn’t be a factor when considering whether to adopt two puppy siblings.

3 early signs of littermate syndrome

Does littermate syndrome always happen? No. However, it can, and you may be able to spot signs in new puppies or young dogs. Knowing what to look out for can empower you to seek help from veterinarians, professional trainers, or behaviorists more quickly.

  1. Separation anxiety. You’ll notice this indicator when dogs are apart, even for just a short period. Dogs experiencing separation anxiety will whine, cry, howl, and be otherwise anxious in these situations.
  2. Difficulties with training. Difficulty in basic obedience training is another potential sign of littermate syndrome. Potty training one dog is not easy, but two, especially when their focus is only on their sibling, can be more challenging. The dogs may be resistant to training because of that.
  3. Aggression. Aggressive behavior is another sign. Dog siblings may play rougher, which can cause severe injuries.

What to know about littermate syndrome

As mentioned above, many dog people have never heard of littermate syndrome. Not every pair of dog siblings will experience littermate syndrome, but there is no way for a potential pet owner to know that. That’s why the general advice is simple: Avoid adopting 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 live together. Dog adoptions of any kind are a complicated undertaking that is best handled on a situation-by-situation basis. Adopting a pair of dogs from the same litter must be done with care, thought, and preparation. Prepare to put in extra time and proper training so your dogs live their best lives.

You will also find that some rescues limit people to adopting one puppy at a time, littermates or not. Some breeders have the same policy.

Is littermate syndrome real?

Despite the conversation and policies, littermate syndrome isn’t a scientific term, and some pet professionals don’t believe it’s real. For some, the sticking point is the use of the word “syndrome.” They fear that new owners with sibling dogs will jump to the rehoming solution too quickly. Syndrome can be an intimidating word, so it’s important to understand what the littermate syndrome can mean and what can be done about it.

In short, it’s a term widely accepted by veterinarians as poor behavior pet experts have observed over many years. It’s not a conspiracy theory against puppies but an accepted phenomenon observed and treated by professionals. For prospective pet parents, it’s best to look at all sides of the conversation when making a decision. Dog psychology and the study of the canine-human bond are ever-evolving.

Sad dog

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

Risks of adopting or purchasing sibling puppies

If you are determined to adopt or purchase a pair of canine siblings, be aware of the risks and have a good plan. That’s the best way to help your dogs overcome any issues they may 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, and nobody wins.
  • 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 may not know how to cope and can go into depression.
  • Jealousy. If one of the pair senses the other is getting more attention, the dog may become aggressive to their sibling or you.
  • Fearfulness. Because the dog has learned to only be comfortable with their sibling, anything else becomes unsafe in their mind.

What to do if you already own a pair of littermates

The first thing to do is to put training first. A happy dog is a confident, well-trained dog. Some pet owners may find that formal training classes are required. However, each dog will need to be trained separately. This separation will help each dog cope with being alone without their sibling. It also makes training easier and more fun for pups and pet parents alike.

Here are some other tips to get you started.

  • Socialize separately — In addition to separate training, make time for solo socialization for each puppy. This might include taking your dogs on separate walks or having them sleep in separate crates.
  • Be attentive to new behavioral issues —It is essential to understand that dogs’ wheels are always turning. They are social animals and often have a perceived social hierarchy in their brains. So, for example, if you take one dog out first, the other may think the first dog is being treated preferentially. Keep an eye on littermate syndrome that turns into sibling rivalry, which can lead to aggression or conflict.
  • Nix family dinners — Individual food bowls are a great idea to help avoid food aggression. If you have other human family members who can help, have each dog do separate things with each person in your household. If you feel the need and have the space, feed your littermate pups in separate rooms.

The bottom line is that you are teaching your dogs how to be OK without their siblings, with whom they have a natural and deep bond.

Is a 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 example currently to back this up. However, anecdotal evidence suggests it is a solution that works for some pet parents.

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 problems with social development.

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

Frequently asked questions

What are the symptoms of littermate syndrome?

Separation anxiety is a hallmark symptom of littermate syndrome. A dog may be anxious when they’re not with their sibling(s). Aggression and training issues are other possible signs.

Is it OK to get two dogs from the same litter?

It’s generally not recommended. Shelters and breeders may not allow it because of the potential for littermate syndrome, a non-scientific but generally accepted term to describe aggressive behavior when two or more dogs from the same litter are raised together.

How long does littermate syndrome last?

It’s unclear. Littermate syndrome isn’t a scientific term, and there’s not much research on it. Training sessions can help curb the issue more quickly, but you have to be willing to put in the hard work when necessary.

What breeds get littermate syndrome?

A common misconception is that some breeds are more prone to the condition than others, but the fact is that any breed can get littermate syndrome. Every dog is different, and not every set of sibling pups will have littermate syndrome if brought home together.