Littermate Syndrome

Bringing home two puppies from the same litter, or buying a second puppy before yours matures (around the age of 2) might seem like double the fun and a great way to ensure your puppy has a friend for life but unfortunately the reality is rarely this fun. Without LOTS of time and effort, most of these pairs will develop littermate syndrome, a behavioral condition that can seriously affect a dog’s emotional development and training success. For this reason I strongly discourage owning two puppies at once, but if you’ve already got them there’s some information below on how to avoid these issues.

What Is Littermate Syndrome?

Littermate syndrome refers to a set of behavioral issues that can develop when two puppies from the same litter (or puppies of the same age raised together) form an unusually strong bond with each other — often at the expense of their bond with humans.

While it’s not a formally recognized medical diagnosis, dog trainers and behaviourists frequently see the pattern: the puppies rely so heavily on each other that they struggle with confidence, socialisation, and independence.

Why Littermate Syndrome Happens

When two young puppies grow up side by side, they naturally become each other’s primary source of comfort and security. Unfortunately, this close attachment can inhibit individual emotional growth.

Here’s what typically happens:

• The puppies depend on each other for reassurance instead of seeking it from their human caregivers.

• They may panic when separated, even briefly. I’ve met pairs who scream and have an anxious meltdown if they’re more than 1m apart which makes leaving the house incredibly stressful for both the dogs and owners. These dogs are so focused on each other that they can’t engage with their owners at all and training becomes almost impossible as a result.

• They often fail to develop independent personalities, making training and socialization more difficult. They’re unlikely to learn to interact with other dogs and therefore don’t develop the social skills needed to be around unfamiliar dogs.

• Over time, competition and conflict may arise as they mature, especially between same-sex siblings. It isn’t uncommon for littermate syndrome conflicts to put the dog’s lives at risk- at this point the dogs must be separated permanently for their own safety and choosing which to rehome is an extremely difficult choice for the owners.

Common Signs of Littermate Syndrome

If you’ve adopted or are raising two puppies together, keep an eye out for these red flags:

• Separation anxiety when one is out of sight of the other.

• Fearfulness around new people, environments, or experiences.

• Difficulty focusing during training, especially when the sibling is nearby.

• Aggression or fighting that escalates as the dogs mature.

• Uneven development, where one pup seems confident and the other increasingly withdrawn.

These behaviors can begin as early as 8–10 weeks and often become more noticeable around adolescence (6 months old)

How to Prevent or Manage Littermate Syndrome

The good news? With structure, patience, and consistent training, you can help littermates grow into well-adjusted, independent dogs. Please bear in mind that this takes hours- every single day- and if you can’t commit to that for several years then it’s best to just buy one- or rehome one of the dogs before they develop littermate syndrome. Prevention is always better than cure!

1. Train Separately

Give each dog one-on-one training sessions every day. This helps them bond with you and learn to focus without their sibling’s influence. I recommend 5-10 minutes at a time, 2-3 times per day for each dog.

2. Encourage Independence

Feed them in separate spaces, take them on solo walks, ensure they sleep in separate rooms and let them spend short periods apart from an early age. Gradually increase the time apart to build confidence. Aim to keep them separated for at least 50% of the time. This is easily achieved in multi-person households where one person can focus on training and play at home while someone else walks the other dog, and then you can switch. Or, when the dogs are resting, one can be in the living room watching TV with one human while the other is upstairs with a different human (finally- a purpose for hibernating teenagers!).

3. Socialize Individually

Expose each puppy to different people, sounds, and environments independently. Individual experiences help shape well-rounded adult dogs. Please check out my socialisation blog to get an idea of the level of exposure you should be aiming for.

4. Seek Professional Help Early

Consulting an experienced dog trainer or veterinary behaviorist is essential if you haven’t raised two puppies together before. Once again, prevention is better than cure and by nipping any issues in the bud you’ll save a huge amount of time, money and stress further down the line.

Should You Adopt Two Puppies at Once?

For most new dog owners, the best approach is to adopt one puppy at a time. Raising one dog allows you to focus on proper training, socialisation, and bonding. Once your first dog is mature and well-adjusted (usually aged 2+) you can decide whether adding another pup makes sense for your family.

However, if you’ve already adopted littermates, don’t panic — awareness, structure, and professional guidance can make all the difference.

Final Thoughts

Littermate syndrome can be challenging, but it’s not insurmountable. With commitment and proactive training, many dog owners successfully raise littermates into happy, confident, and independent companions.

The key is balance: help your dogs build a strong bond with you as their leader, while also developing their own sense of security and individuality.