I never set out to specialise in littermate syndrome. I rather accidentally slipped into it after my own experience with Lucy and Shelby, two littermate coonhounds in my family. Since then, I’ve helped dozens of families raising littermates and similarly aged puppies make real progress — alongside spending years working through these problems in my own home.
That doesn’t mean I think “littermate syndrome” is a neat, scientifically established diagnosis. It isn’t. But the behaviours people use the term to describe — overdependence, difficulty coping apart, escalating conflict, poor social skills and struggles developing confidence as individuals — can be very real. I’ve seen them repeatedly, both professionally and at home.
And if you’ve already brought home two puppies, please don’t read this as a prediction of disaster. Two puppies are not doomed to develop problems. What matters now is helping them learn that they can be safe, confident and functional both together and as individuals.
What Is Littermate Syndrome?
Littermate syndrome is an informal term used to describe a cluster of behavioural problems that can develop when two puppies of a similar age are raised together and become excessively dependent on one another.
Despite the name, the puppies do not have to be biological littermates. I’ve seen similar difficulties in puppies from different litters who are close in age and spend most of their early life together.
The issue isn’t simply that the puppies “love each other too much.” The concern is that they may get so much security, stimulation and social feedback from one another that important individual skills don’t develop as well as we’d like. One or both puppies may struggle to cope alone, focus without the other dog present, build confidence independently or communicate appropriately when their sibling doesn’t listen to their boundaries.
Is Littermate Syndrome Real?
This is where I want to be careful with language. Littermate syndrome is not a formal veterinary or behavioural diagnosis, and we don’t have good research establishing it as one distinct syndrome with one predictable cause and outcome.
I actually used to dismiss the term for exactly that reason. Then I joined Lucy and Shelby’s family and started seeing the behaviours first-hand. Later, I began working with more families experiencing remarkably similar problems.
So I don’t use “littermate syndrome” to mean that every pair of siblings will develop a specific disorder. I use it as convenient shorthand for a pattern of problems we can actually observe and work on. The label matters far less to me than the individual dogs standing in front of me.
My Experience With Lucy & Shelby
Lucy and Shelby are littermate coonhounds. Mr Rebarkable raised them before I became part of their family, and he’d done a lot right — but nobody had warned him that raising two puppies together could create some very particular challenges.
When I first came into their lives, I didn’t immediately call what I saw littermate syndrome. I wasn’t particularly convinced by the concept at the time, and coonhounds are their own special brand of dog, so I wanted to understand what was actually happening rather than slap a label on it.
The problems became difficult to ignore:
- They had very little tolerance for one another. This could escalate into serious fighting.
- Their dog-to-dog communication wasn’t great. Bringing my German Shepherd, Indie, into the family highlighted how easily communication could go wrong.
- They resource guarded. Space was a particularly important resource for our girls.
- Play escalated too quickly. What began as perfectly normal bouncy play could tip into conflict remarkably fast.
- They struggled to function as true individuals. A lot of our work became about giving each dog room to develop her own confidence, preferences and coping skills.
Signs of Littermate Syndrome I Actually Watch For
I don’t diagnose littermate syndrome from one behaviour. Two puppies playing wildly together doesn’t prove anything, and neither does one puppy being upset the first few times they’re separated.
I’m more interested in patterns, particularly when several of these happen together:
- Significant distress when separated. One or both dogs struggle to settle, eat, train, walk or engage without the other.
- Difficulty focusing independently. The sibling is consistently more important than the human, environment, food or task.
- One puppy borrowing the other’s confidence. Together they appear bold, but individually one or both struggle with situations they normally navigate as a pair.
- Escalating play. The dogs repeatedly fail to disengage or respond to requests for space until play tips into conflict.
- Resource guarding or conflict. Food, toys, resting places, doorways, attention or access to people can become points of pressure.
- Poor boundaries. One dog repeatedly invades the other’s space and doesn’t respond appropriately to subtle requests to stop.
- Difficulty developing separate relationships. Each puppy has relatively little experience interacting, learning and exploring without the sibling present.
- Different behaviour when apart. Sometimes separating the pair reveals a much more relaxed, responsive or confident dog than you normally see when they’re together.
The last point is particularly useful. Separation isn’t just something we use to change behaviour; it can help us understand the dogs. I want to know who each puppy is when the other puppy isn’t influencing the picture.
Why Can Raising Two Puppies Together Be Difficult?
Puppyhood is when we’re asking a dog to learn an enormous amount about the world: how to be alone, how to settle, how to communicate with different dogs, how to interact with people, how to cope with frustration, how to explore unfamiliar environments and how to recover when something feels difficult.
When another puppy is present for almost every one of those experiences, it’s very easy for the pair to practise being a unit rather than practising those skills independently.
That doesn’t mean their relationship with each other is bad. I want puppies who live together to enjoy one another. The goal is simply to make sure their sibling isn’t their only route to feeling safe, having fun or navigating the world.
If you’re still deciding whether to bring home a pair, I’ve covered the practical side separately in Should You Get Two Puppies at Once?. This article is primarily for understanding and managing the behavioural problems people call littermate syndrome.
Can Unrelated Puppies Develop Littermate Syndrome?
They can develop the same kinds of problems. Biological siblinghood isn’t the part I’m most interested in as a trainer. Age, developmental stage, temperament, the amount of time the puppies spend together and how many independent experiences they have are much more useful things for me to look at.
Two unrelated puppies close in age can become highly dependent on one another. Equally, two actual littermates can be raised together without developing severe behavioural problems. That’s another reason I dislike treating the label as a diagnosis or an inevitability.
How to Prevent Littermate Syndrome
If you already have two puppies, the answer isn’t to keep them permanently apart. It’s to deliberately create opportunities for them to learn independently as well as together.
- Train them separately. Even five or ten minutes of individual training gives each puppy practice engaging with you without their sibling.
- Give them solo walks and outings. They need opportunities to experience the world without using the other puppy as a social crutch.
- Teach independent rest. Each puppy should be able to sleep and settle without needing physical access to the other.
- Feed separately. This removes unnecessary pressure and gives both dogs space around a valuable resource.
- Give each puppy one-to-one time. Play, cuddle, train, sniff, explore — whatever that individual puppy enjoys.
- Socialise them as individuals. Socialisation isn’t just meeting dogs. It’s learning that the world is safe and manageable. Each puppy needs their own experiences.
- Supervise play. Don’t wait for play to become chaotic before intervening. Help them take breaks while everybody is still having fun.
- Protect boundaries. If one puppy asks for space and the other ignores them, step in. Don’t make the dog asking politely escalate to get heard.
You don’t have to create two completely separate lives. That’s unrealistic for most families. You’re simply making sure each puppy regularly practises being an individual.
What If You Already Have Littermates and You’re Struggling?
First, don’t panic and don’t assume you’ve ruined your dogs. I’ve worked with dozens of families at this point, and progress is absolutely possible.
I usually start by reducing pressure rather than adding more training. If the dogs are constantly rehearsing conflict, competing for resources or becoming overstimulated together, asking for more obedience in the middle of that isn’t necessarily useful.
1. Create genuinely separate downtime
Use rooms, pens, baby gates or crates where appropriate so each dog gets proper rest. With Lucy and Shelby, separate sleeping spaces were pivotal. We tried crates with a pony wall between them, but separate rooms worked much better for our girls.
2. Remove predictable conflict
Feed separately. Manage high-value chews and toys. Pay attention to beds, sofas, doorways and human attention if those create tension. Management isn’t failure; it stops the dogs rehearsing behaviour we’re trying to change.
3. Learn each dog’s early communication
Don’t wait for a growl, snap or fight. Watch for freezing, turning away, moving away, stiffness, hovering, blocking access, persistent following or one dog repeatedly trying to end an interaction. Advocate for the dog who’s asking for space.
4. Build independence gradually
Separate walks, training, enrichment and outings help each dog learn to function without the other. If separation itself causes distress, make the first steps easy enough that the dog can actually cope rather than simply forcing longer periods apart.
5. Give them decompression
When dogs are living with repeated social pressure, rest matters. Sniffing, chewing, quiet solo time and lower-pressure days can all help bring arousal down. We found that life became much easier when we stopped expecting Lucy and Shelby to be together simply because they were sisters.
What If Your Littermates Are Fighting?
If the dogs are already having serious fights, I would treat that as a safety and behaviour problem rather than trying to solve it by making them “work it out.” Repeated fights can make future conflict easier to trigger and can obviously result in significant injury.
Prevent further rehearsals while you work out what’s driving the conflict. That may mean physical separation, rotating access to parts of the home, separate feeding and carefully managed shared time. If fights are intense, injuries are occurring, or you’re frightened of handling the situation, bring in a qualified force-free behaviour professional. The American Veterinary Society of Animal Behavior recommends reward-based methods for behavior modification and provides guidance on choosing an appropriate trainer or behavior consultant. A veterinary assessment is also sensible when behaviour changes suddenly or pain could be contributing.
Do You Have to Rehome One Puppy?
No. I don’t think owning littermates automatically means one needs to be rehomed, and I certainly wouldn’t jump to that conclusion because somebody has noticed early warning signs.
There are situations where rehoming one dog may ultimately give both dogs a safer and happier life, particularly where serious conflict cannot be safely managed or the household simply cannot meet the dogs’ individual needs. But that’s a case-by-case welfare decision, not a standard treatment for “littermate syndrome.”
Before making that decision, I want to understand the individual dogs, the severity of the behaviour, the family’s capacity for management, whether pain or medical issues are involved, and whether a realistic behaviour plan has been tried.
Can Littermate Syndrome Be Fixed?
Dogs can make enormous progress. I prefer that wording to promising a “cure,” because we’re usually working on several behaviours rather than one disease called littermate syndrome.
A dog can learn to settle alone. They can become more confident independently. Sibling play can become safer. Resource guarding can be managed and worked on. The dogs can develop better relationships with their humans and more appropriate social skills.
How far an individual pair progresses depends on the dogs, what behaviours have developed, how long they’ve been practising them and what their household can realistically implement. I don’t expect perfection. I look for safer dogs, lower stress and a household that works.
How Are Lucy & Shelby Doing Now?
This is probably the part I most wanted to update, because the original version of this article was written while we were still very much in the middle of working through things.
Lucy and Shelby are doing phenomenally better.
We haven’t had a fight in years.
That doesn’t mean I decided the problem was “fixed” and put them straight back into the exact environment that caused trouble. We changed how we live with them. They get individual experiences. We manage their space. We don’t manufacture competition. We pay attention when one dog needs a break. And we’ve learned an enormous amount about who Lucy and Shelby are separately, not just who they are as “the hounds.”
These days they can enjoy life together without the constant conflict we used to see. That’s the outcome I want people to understand is possible: not necessarily two dogs who suddenly become inseparable best friends, but two individuals who can feel safe, have their needs met and live successfully in the same family.
Littermate Syndrome FAQs
Does littermate syndrome always happen?
No. Raising two littermates together does not guarantee behavioural problems. Think in terms of risk and individual development rather than inevitability.
What age does littermate syndrome start?
There isn’t a scientifically established age at which a syndrome suddenly appears. Problems may become more noticeable as puppies mature, become more independent, enter adolescence or begin experiencing more competition and social conflict.
Can littermate syndrome happen with a male and female?
Yes. I wouldn’t assume a pair is safe from dependency or conflict simply because they’re opposite sexes. Look at the actual relationship and behaviour of the individual dogs.
Should littermates sleep together?
I want each puppy to be capable of sleeping and settling independently. That doesn’t mean they can never nap together, but routinely practising separate rest is valuable. For Lucy and Shelby, separate sleeping spaces made a major difference.
Should you train littermates separately?
Yes, at least some of the time. Individual training gives each puppy a chance to focus, learn and build a relationship with you without constantly referencing their sibling.
Can littermate syndrome happen with puppies from different litters?
Similar behavioural problems can develop in unrelated puppies of a similar age. That’s why I focus less on whether they share DNA and more on whether each puppy is developing the ability to function independently.
The Goal Isn’t to Break Their Bond
This is the thing I wish more people understood about working with littermates. I’m not trying to make siblings dislike one another or stop them having a relationship.
I’m trying to give them more options.
I want each dog to be able to rest without the other. Explore without the other. Learn without the other. Build relationships without the other. And then, when they’re together, I want that relationship to be something they can enjoy rather than something they cannot function without.
That’s what eventually changed life with Lucy and Shelby, and it’s what I now help other families work towards too.
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