Littermate Syndrome in Dogs: How to Raise Two Puppies Successfully

By Dr Duncan Houston.

Raising two puppies together can be joyful, chaotic and considerably more demanding than raising one. You are not simply adding another food bowl. You are doubling the housetraining, socialisation, supervision, veterinary care and individual training required during a critical developmental period.

“Littermate syndrome” is commonly used to describe excessive dependency, poor confidence, separation distress, training difficulty or conflict in puppies raised together. However, it is not a clearly defined or scientifically validated veterinary diagnosis. These problems are possible, but they are not inevitable and they are not exclusive to biological littermates.

The most useful approach is to forget the scary label and concentrate on raising each puppy as an individual.

Quick Answer

If you are raising two puppies together:

Train each puppy separately every day.
Provide individual walks and socialisation experiences.
Teach them to rest and remain alone without each other.
Feed separately and provide multiple resources.
Housetrain each puppy individually.
Reward independent engagement with people.
Supervise play and interrupt it before it escalates.
Continue enjoyable time together.
Watch for fear, dependency, guarding or aggression.
Seek qualified help early if problems emerge.

You do not need to keep the puppies apart constantly. The goal is a healthy balance between shared experiences and individual development.

What Is Littermate Syndrome?

“Littermate syndrome” is an informal umbrella term used for behavioural problems sometimes reported when two puppies of a similar age are raised together.

Reported concerns include:

Distress when separated
Reduced attention during training
Difficulty engaging with people
Fearfulness in unfamiliar environments
Poor confidence when alone
Overexcitement when together
Resource guarding
Conflict during adolescence
Different development between the two puppies
One puppy consistently overshadowing the other

The puppies do not need to be biological siblings. Similar concerns may develop in two unrelated puppies raised together with few independent experiences.

Is Littermate Syndrome Scientifically Proven?

There is limited scientific evidence supporting “littermate syndrome” as one specific condition caused by raising siblings together.

The individual behaviours associated with the label are real, but each may have different causes, including:

Genetics
Prenatal and early-life experiences
Inadequate socialisation
Lack of individual training
Separation-related distress
Fear
Resource guarding
Pain or illness
Chronic overarousal
Household management
Normal changes during adolescence

The IAABC Foundation has noted the lack of scientific literature establishing a distinct syndrome and cautions that not all littermates raised together develop serious problems. IAABC Foundation Journal

Texas A&M veterinary guidance similarly describes the reported behavioural pattern while emphasising that it is not a guaranteed outcome for puppies raised together. Texas A&M School of Veterinary Medicine

Calling every problem “littermate syndrome” can distract from assessing what is actually happening with each dog.

Should You Adopt Two Puppies Together?

For many households, adopting one puppy at a time is the more manageable choice.

Consider two puppies only if you can realistically provide:

Separate daily training
Separate socialisation
Individual veterinary care
Multiple safe resting areas
Separate feeding
Frequent supervision
Gradual alone-time training
Additional financial resources
Help from a qualified trainer when needed
A long-term plan if conflict develops

If you are already raising two puppies, do not panic. You do not need to rehome one simply because you encountered the term online.

Instead, assess whether both puppies are developing confidence, learning independently and coping comfortably when separated.

Why Raising Two Puppies Is More Difficult

Puppies naturally attract each other’s attention. Another puppy is usually more exciting than a person repeating “sit” while holding a piece of kibble.

When puppies spend nearly all their time together:

They may distract each other during training
Individual stress signals may be missed
One puppy may copy the other’s fear
Housetraining accidents become harder to monitor
Recall may be less reliable
They may struggle when separated
Play may replace human interaction
One puppy may dominate access to resources
Different personalities may become hidden

This does not mean their relationship is unhealthy. It means their individual needs require deliberate attention.

The Puppy Socialisation Period

Early puppyhood is a particularly important time for learning about people, environments, surfaces, sounds, animals and routine care.

Each puppy should have individual opportunities to experience:

Different people
Calm, suitable dogs
Vehicle travel
Veterinary handling
Grooming
Household noises
New surfaces
Streets and parks
Being alone briefly
Resting away from the other puppy
Training around mild distractions

Socialisation is not simply exposure. The experience should be safe, gradual and positive.

The American Veterinary Society of Animal Behavior supports appropriately managed puppy socialisation before the vaccination course is fully completed, with precautions based on local disease risk and veterinary advice. AVSAB Puppy Socialisation Position Statement

Raise Two Individuals, Not a Matching Set

Your puppies may share parents, a birthday and a talent for dismantling furniture, but they remain separate individuals.

Each puppy should have their own:

Name
Identification
Training goals
Veterinary record
Insurance policy where applicable
Food requirements
Resting space
Enrichment preferences
Relationship with family members
Pace of social development

Avoid constantly comparing them. One puppy may learn quickly while the other needs more repetition. One may be confident outdoors but cautious with handling.

Train the puppy in front of you, not the puppy standing beside them.

Step 1: Build Individual Human Bonds

Spend calm one-on-one time with each puppy every day.

This may include:

Hand-feeding part of a meal
Gentle play
Grooming practice
Relaxing together
Short training sessions
Individual walks
Exploring a new environment
Practising handling
Quiet enrichment

Bonding does not require constant excitement. Calm, predictable interactions are often just as valuable as play.

Encourage each puppy to seek guidance, rewards and comfort from people rather than relying exclusively on the other dog.

Step 2: Train Each Puppy Separately

Begin training in different rooms or behind a visual barrier.

Teach each puppy:

Their name
Eye contact
Hand targeting
Sit
Down
Come
Leave it
Drop
Go to bed
Settle
Loose-lead walking
Waiting at doors
Calm handling

Keep sessions brief and reward-based.

Once each puppy understands a skill individually, practise with both puppies present. Expect the difficulty to increase substantially when their favourite furry distraction enters the room.

Step 3: Create Separate Resting Spaces

Each puppy needs a comfortable place where they can sleep without being climbed on, chewed or invited into another wrestling tournament.

Options include:

Separate crates
Individual exercise pens
Beds on opposite sides of a gated area
Puppy-proof rooms
Separate resting zones within the same room

Separate crates can initially be positioned near each other. Gradually increase the distance as both puppies become comfortable.

Do not suddenly isolate a puppy who has never slept away from their sibling. Build independence gradually.

A puppy who panics inside a crate may cope better in a pen or puppy-proof room.

Step 4: Practise Gradual Separation

Begin when both puppies are relaxed.

A simple progression may include:

Give each puppy an enrichment toy on separate beds.
Position them a short distance apart.
Place a baby gate between them.
Move one puppy briefly into another room.
Return before either puppy becomes distressed.
Gradually increase time and distance.
Practise with each puppy remaining at home alone.

Use a camera when beginning out-of-sight or home-alone training.

The objective is not to make the puppies stop caring about each other. It is to teach them that temporary separation is safe.

Signs Separation Training Is Moving Too Quickly

Reduce the difficulty if either puppy:

Stops eating
Paces
Pants when not hot
Vocalises continuously
Scratches at doors
Attempts to escape
Trembles
Cannot settle
Fixates on finding the other puppy
Toilets despite being recently taken outside
Becomes increasingly distressed instead of recovering

Do not repeatedly allow a puppy to panic in the hope they will “get used to it”. Severe distress can strengthen the negative association with separation.

Step 5: Walk the Puppies Individually

Walking two untrained puppies together may produce more tangling than training.

Individual walks help each puppy learn to:

Respond to their own name
Follow the handler
Walk on a loose lead
Explore without copying the other puppy
Recover from unfamiliar sights and sounds
Check in with a person
Build confidence independently

Walks do not need to be long. Quality, safety and positive exposure are more important than distance.

Once both puppies have reliable individual skills, add short walks together.

Step 6: Socialise Each Puppy Individually

Take each puppy on separate, carefully planned outings.

Examples include:

Sitting outside a quiet café
Visiting a calm friend
Walking through a quiet car park
Watching traffic from a comfortable distance
Visiting the veterinary clinic for treats
Attending an appropriate puppy class
Exploring safe surfaces and environments

Avoid overwhelming either puppy. A confident sibling should not be used to drag a frightened puppy towards something they are trying to avoid.

Some shared outings are valuable, but individual experiences reveal how each puppy genuinely feels.

Step 7: Housetrain Puppies Separately

Take puppies outside individually whenever practical, particularly while they are learning.

This allows you to:

See which puppy eliminated
Reward the correct puppy immediately
Identify individual schedules
Notice diarrhoea or urinary changes
Prevent play from replacing toileting
Teach a toileting cue

Take each puppy out:

After waking
After meals
After drinking
After play
Before confinement
After confinement
When sniffing, circling or becoming restless

Clean accidents with an enzymatic cleaner and never punish either puppy.

Step 8: Feed Separately

Feed puppies in separate areas from the beginning.

Separate feeding:

Prevents one puppy stealing food
Allows accurate appetite monitoring
Supports individual diets
Reduces competition
Helps identify vomiting or reduced appetite
Makes medication easier
Prevents rehearsing food guarding

Pick bowls up after meals.

Provide chews and high-value food toys only with appropriate separation and supervision. Do not repeatedly remove food to “test” whether a puppy will guard it.

Step 9: Provide Multiple Resources

Each puppy should have access to their own:

Food bowl
Water access
Bed
Safe retreat
Toys
Chews
Training time
Human attention

Increase distance between resources if one puppy blocks or intimidates the other.

Watch for subtle competition, including:

Hard staring
Standing over the other puppy
Blocking doorways
Taking every toy
Preventing access to water
Guarding people
Repeatedly interrupting rest
One puppy consistently retreating

A lack of growling does not necessarily mean both puppies feel comfortable.

Step 10: Supervise Play

Healthy puppy play often includes:

Loose, wiggly bodies
Play bows
Role reversals
Pauses
Taking turns chasing
Returning voluntarily after breaks

Pause play if you notice:

Stiff posture
Persistent pinning
Repeated attempts to escape
One puppy hiding
Continuous chasing without role reversal
Guarding
Yelping followed by continued pressure
Escalating vocalisation
Biting that does not stop after a pause
One puppy repeatedly overwhelming the other

Call the puppies apart, reward them and provide a calm break.

Do not wait until both puppies are exhausted and irritable. Overtired puppies make decisions with all the wisdom of tiny, furry nightclub patrons at closing time.

Teach the Puppies to Settle

Two puppies can keep each other awake and overexcited.

Reinforce:

Lying quietly
Resting on separate mats
Chewing calmly
Choosing independent beds
Relaxing while the other puppy moves
Remaining settled during household activity

Schedule regular rest periods. Puppies need considerable sleep, and excessive biting, zooming or rough play may indicate overtiredness rather than insufficient exercise.

Do Not Keep Them Apart Constantly

Independence training should not eliminate their relationship.

Allow enjoyable shared activities such as:

Supervised play
Calm parallel walks
Resting together when appropriate
Training with both puppies present
Exploring secure areas
Family time

The aim is flexibility. Each puppy should function both with and without the other.

Constant separation can be impractical and may unnecessarily prevent healthy social interaction.

A Practical Daily Structure

A manageable day might include:

Together:

Supervised morning play
A short family training session
Calm parallel walking
Resting in the same room
Evening social time

Individually:

Five-minute training sessions
Toilet trips
Short walks or outings
Handling practice
Alone-time training
Meals
Time with different family members

The exact schedule depends on the puppies’ ages, health and temperament. You do not need to divide every minute perfectly. Consistent individual opportunities matter more than military precision.

What Happens During Adolescence?

As puppies mature, their behaviour and social relationship may change.

You may notice:

Increased independence
More intense play
Resource guarding
Reduced tolerance
Sexual behaviour
Reactivity
Competition
New fears
Conflict around people or resting places

These changes are not proof that “littermate syndrome” has suddenly appeared. Adolescence, hormones, pain, learning history and environmental stress may all contribute.

Arrange a veterinary examination if behaviour changes suddenly. Medical problems can lower tolerance and increase irritability.

When Puppy Conflict Becomes Serious

Seek professional help if:

Fights cause punctures or injuries
One puppy repeatedly targets the other
Conflict is becoming more frequent or intense
There is guarding around food, toys, beds or people
One puppy appears frightened in the other’s presence
The puppies cannot be safely interrupted
Tension continues after the original resource is removed
Either puppy redirects aggression towards a person
You are changing normal life to prevent fights

Do not let them “fight it out”. Rehearsed conflict may worsen and injuries can be severe.

Separate the puppies safely using gates, pens, doors or secure rooms until professional assessment.

What to Do During a Fight

Avoid reaching between fighting dogs or grabbing collars with your hands.

If possible:

Use a physical barrier
Close a door between them
Place a large object between the dogs
Move other people and animals away
Allow both dogs time to calm separately
Check carefully for injuries
Seek veterinary care for wounds

Puncture wounds can look small while hiding deeper tissue damage. Any dog injured in a fight should be assessed by a veterinarian.

After a serious incident, keep the dogs separated and obtain behavioural guidance before attempting another interaction.

Medical Problems That Can Affect Behaviour

Not every problem between two puppies is behavioural.

Arrange veterinary assessment if either puppy develops:

Sudden irritability
Reluctance to play
Lameness
Sensitivity to touch
Reduced appetite
Vomiting or diarrhoea
Urinary accidents
Sleep disturbance
Neurological signs
Sudden fear or aggression

Pain, illness and developmental problems may affect learning, tolerance and social behaviour.

Choosing Professional Help

Look for a professional who:

Uses reward-based methods
Assesses each puppy individually
Observes the puppies together
Considers health and pain
Creates a realistic household management plan
Has recognised behaviour or training qualifications
Works with your veterinarian
Refers serious cases to a veterinary behaviourist

Avoid trainers who:

Blame one puppy for being “dominant”
Recommend physical punishment
Use shock, prong or choke collars
Deliberately provoke fights
Guarantee results
Advise sudden prolonged separation without assessment

Should One Puppy Be Rehomed?

Rehoming is not automatically required.

It may need to be considered when:

Serious aggression persists
One or both puppies have poor quality of life
Safe management is not possible
The household cannot provide individual care
Injuries have occurred
Professional assessment indicates ongoing risk
The puppies’ needs are fundamentally incompatible

This decision should be made with support from the breeder, rescue organisation, veterinarian and qualified behaviour professional.

Early, carefully managed rehoming may sometimes be kinder than allowing chronic fear or conflict to continue. It should not be treated as punishment or failure.

Common Mistakes

Doing Everything Together

Shared routines are convenient, but puppies also require independent learning.

Separating Them Abruptly

Independence should be developed gradually rather than through sudden prolonged isolation.

Training Only One Puppy

The quieter puppy may need just as much individual attention as the obvious troublemaker.

Letting Them Compete for Food

Separate feeding prevents conflict and allows health monitoring.

Assuming Rough Play Is Always Harmless

Watch whether both puppies remain willing participants.

Punishing Growling

Growling communicates discomfort. Identify the cause and change the situation.

Waiting for Adolescence to Start Training

Independence, handling and socialisation should begin during early puppyhood.

Believing Problems Are Inevitable

The label does not predict your puppies’ future. Their individual behaviour and welfare matter more.

Frequently Asked Questions

Is littermate syndrome a real diagnosis?

No single validated veterinary diagnosis or test defines littermate syndrome. It is an informal term for several behavioural concerns that may have different causes.

Does it only affect siblings?

No. Similar dependency, training and conflict problems may occur in unrelated puppies of a similar age raised together.

Should littermates sleep in separate crates?

Separate sleeping skills can be useful, but introduce them gradually. Crates may initially remain close together before distance is increased.

Can the puppies attend the same training class?

Possibly, but they should work with separate handlers and maintain enough distance to concentrate. Separate classes may be more useful if they cannot focus.

Should they always be walked separately?

Individual walks are important during training, but calm walks together can also be included once each puppy has basic lead skills.

Can two puppies still bond with their owners?

Yes. Regular individual training, play, handling and quiet time can build strong relationships with people.

Will desexing prevent conflict?

Desexing may influence some hormonally associated behaviours, but it does not replace training, management or behavioural assessment. Discuss timing with your veterinarian.

Is adopting one puppy easier?

Usually. Raising one puppy allows more time for individual socialisation, training and supervision. A second dog can be considered once the first is mature and well established.

Final Thoughts from Dr Duncan Houston

“Littermate syndrome” is not a guaranteed fate and should not become a frightening label applied to every pair of puppies.

The practical concern is whether each puppy receives enough individual training, socialisation, rest, human connection and experience coping without the other. Raise them as two separate dogs who also happen to enjoy living together.

With planning, patience and a substantial supply of tiny treats, two puppies can grow into confident, well-adjusted adults.

Need Help Raising Two Puppies?

If your puppies cannot focus separately, panic when apart, compete over resources or have started fighting, ASK A VET™ can help you decide what to do next.

Share videos of their interactions, explain your daily routine and discuss any health or behavioural changes with the veterinary team. You can receive practical guidance for training, separation, household management and determining when specialist support is needed.

Visit AskAVet.com or download the ASK A VET™ app for personalised support with puppy behaviour, training and ongoing health.

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About the author

Dr Duncan Houston

Veterinarian · Founder of ASK A VET

Every ASK A VET article is written and reviewed by qualified veterinarians.

About Dr. Duncan →drduncanthevet

Littermate Syndrome in Dogs: How to Raise Two Puppies Successfully