A Tale of Two Siblings: Littermate Syndrome in Dogs


The idea of adopting littermate puppies can seem like an adorable, fun idea. They’ll play with each other, keep each other company, and they’re guaranteed to get along. Right? Unfortunately, not so much.

Let’s talk about littermate syndrome and why bringing home littermates can be a recipe for disaster.

But for those of you who already have sibling pups at home, we’ll also talk about proactive ways you can survive the growth and development of sibling puppies without sacrificing your sanity and the pups’ well-being.

What is littermate syndrome, and why should I think twice about adopting littermate puppies?

  • Littermate syndrome is an anecdotal term that refers to a host of issues that tend to present when siblings are raised in the same household beyond the normal 8-10 weeks.
  • Littermate Syndrome Issue 1: Lack of Training and Socializing
    • Training, socializing, housetraining, and caring for two young puppies can be more difficult than you’d imagine. Often certain components of puppy rearing are lost or done halfheartedly when there’s more than one pup, as so much time is dedicated to “surviving the madness.”
  • Littermate Syndrome Issue 2: Hyperattachment
    • Littermate puppies can quickly become hyperattached, unable to cope without the presence of the other. Often one pup suffers with this more than the other. If this happens, you’ll generally see frantic, panicked, fearful, or even aggressive behavior when the pups are separated.
  • Littermate Syndrome Issue 3: Inter-Dog Aggression 
    • Especially among same-sex siblings, fighting can become severe, even dangerous, as they reach maturity. Siblings often play hard, and fight harder.
    • Because many sibling pups are only socialized with each other, they may develop aggression or fear towards other dogs.

What if I’ve already brought home littermate puppies?

Don’t panic! In many cases, littermates can grow up to lead normal, healthy lives in the same household.

Here’s what you need to know:

  • Give the puppies periodic time apart every single day. That means they should be regularly walked separately, played with separately, and trained separately.
  • Do not allow the pups to share a crate.
  • Feed meals separately, and out of two separate bowls.
  • Remember that both dogs are individuals. They will have unique personalities, may be motivated differently, and may have different energy levels and quirks.
  • Bond with the puppies individually, so that they are able to focus on you and not solely with each other.
  • Socialize the puppies heavily between 8-16 weeks of age. They must meet people and other animals without their sibling present, and should be taken to novel locations separately. Worried about vaccines? Take a look at the American Veterinary Society of Animal Behavior’s recommendations.

Need professional guidance on your littermate issues? We offer private and group online dog training that’s accessible from anywhere in the world. More details here, or contact us.

22 thoughts on “A Tale of Two Siblings: Littermate Syndrome in Dogs

  1. I understand this article is a few months old now, but I am having very similar issues with two completely unrelated dogs, not even the same age or the same breed. Are there articles on non siblings behaving this way? One is a male Maremma Sheepdog named “Fionn”, I’ve had him since he was 10 weeks old, he was 1 and 1/2 and very bonded to me and my older 4 yr old Aussie when I brought home an 8 week old male Australian Shepherd named “Bear”. The minute I introduced Bear to Fionn, Bear ran right up to that 90 lb. dog and initiated play with him like he’d known him his whole life.

    I had to watch them as they were very rough with their play from day one and the size difference was concerning. They will tirelessly play at every opportunity, even now, ignoring both myself and the other Aussie on the farm. If I try to engage one, the other will wedge themselves into the situation (Playing fetch with Bear, Fionn will chase Bear and try to grab him while he’s running back with the ball. If I try to pet Fionn, Bear will start mouthing Fionn’s face and cheeks). They then engage in play with each other right away after they disrupted the activity. They behave this way towards the other Aussie as well, if she tries to play, they will intentionally exclude her. They are inseparable and now Bear is starting to teach Fionn (who is now over 2 years old, while Bear is 9 months) all kinds of bad habits. It is like they made their own separate mini pack and no one else is allowed to join.

    I can’t call Bear unsocialized though. He loves meeting new people and dogs. I started obedience classes with him and he’s doing great (aside from serious issues keeping his focus on me), but Fionn can’t stand it. He loses it when I leave with Bear and any time I exit the gate with Bear for a training session where Fionn can’t interfere. He huffs his cheeks, cries, whines, wails, even howls like he’s in pain.

    Would building a kennel for Bear and only allowing supervised time out correct this obsession between them or should I seriously consider re-homing one before the problems get worse and possibly escalate into fighting?

    1. Having two same sex dogs can lead to many fights as they compete for rank. Always best if having more than one to get opposite genders (however have to be careful if they are too young to be neutered/spayed)

  2. I began to notice this. I now feed separately. They spend at least 3-4 hours a day kenneled seperately, nor even next to each other. We also take them out seperately. I do not want to re-home either but do notice the aggressive behavior between them Occassionally. Do I separate & put them in their kennels or let them fight it out?

    1. We have two goldendoodle sisters that are just past the 6 months age mark, they sleep separately at night and do like having alone time from each other throughout the day, but we do notice the aggression towards each other. What we do is separate them so that we assert our dominance, giving them almost a time out so they can calm down. But then we let them fight again so that they will be able to learn when too much is too much by when we separate them or let them fight. And if you are worried about them getting too rough with each other, we always have two toys handy to give to each of the puppies to distract them.

  3. My littermate males are 3 years old. They are two of my pack of 7, so they have plenty of interaction with other dogs. They do sleep in separate crates now, after about 12 weeks old. Their own personalities have developed nicely, Dale is more loving and clingy to me, while Chip is more independent. I guess mine were easy as littermates because there was a larger pack.

  4. I love how they say socially between 8 to 16 weeks but all vers and animal facilities won’t let you in under about 20 weeks to socialize. I’m not sure what the professionals think we should do we can’t just NOT socialize a puppy until it’s 20 weeks. But everyone shines on you suggested it.

    1. Rachel, in answer to your comment, before they are fully vaccinated, puppies can be carried when they are out and about, so they can be introduced to the world via sight, sound, smell, and touch in some cases. They can watch other dogs, people and children. If you have friends with vaccinated, friendly dogs, then they can meet them. You can have a puppy on your knee and the dog can be brought in on a lead and allowed to sniff the puppy, etc. Once the vaccinations are in place, you can start to take them to environments which enable calm introductions to other pups and dogs, and also watching them from a safe distance. The ideal is to meet other pups and dogs one to one, so they don’t get too hyper. Near my home there is a large park with grass, plants, river, lake, etc., and owners of small dogs and puppies often walk them there during times when children are in school. That sort of place is an ideal environment for a puppy to explore; see pushchairs, prams, toddlers, and generally grow in confidence.

    2. They won’t let you in that young to socialize because the puppy at that age would not have had all of his or her vaccines by then. It’s medically dangerous to socialize dogs in any surroundings when one could be a carrier of something serious and a puppy hasn’t been guarded against it yet. So to err on the safe side to keep a pup from getting an incurable death sentence, play time has to wait.

      1. I agree Kaitlyn puppies dont need to socialize until ti has all its needles while you waite for this you can get them used to you and there surroundings, their new home

  5. My litter mates are 14 years old, one male and one female . They have totally different personalities and needs. One is very outgoing and energetic while the other has always been somewhat neurotic. We have done most of what is in the list, more by instinct than any knowledge. Today is the first time I’ve ever heard of litter mate syndrome.

  6. My dogs are two year old pitbulls both very strong personalitys and from the same litter 2 weeks ago I noticed that they’ve been fighting and last night and this morning they literally tried to kill each other what do I do? Give the one away or put one down I need advice asap as I love both my dogs and am scared they might kill each other

  7. My partner and I were unaware of this issue until it was too late and the dogs began fighting. We now have them seperate nearly all the time out of fear that they will keep fighting and cause each other serious damage. We have a little one on the way and are looking at moving for work I doubt we will be able to keep them separate like we have been. What can we do now to reintegrate them to being together more often? I’m not willing to rehome them they are apart of our family and I’ll do what I have to to make it work.

    1. I have a vet friend who raised two males from a Giant Schnauzer together, not knowing this either. They need to always have one crated or there is serious damage. She once asked me to come into the clinic with her so she could sew up Thunders’ leg, as he would have bitten anyone else. Vets do not have enough regular training in school on raising healthy puppies
      to advice clients on behavior.

  8. I had two littermate lab sisters – completely diffrent personalties – loved each other deeply and very loyal to one another but never any glaring issues. When puppies it was impossible to train them when together – they would make eye contact and off they were. so I separated, walked separate and one-on-one time with both. I did this more out of sanity since I saw that training them together wasn’t possible. Once they reached maturity and trained – all was well. I never heard of littermate syndrome until recently.

  9. I have 2 female littermates (about a yr n a half old), they’re german shepherds. I’ve basically done everything it says about raising littermates. However, both of the girls came in heat at basically the same time. I had my partner bring our male down to breed them (one of the sisters belongs to him). Even tho I put him with each girl separately, switching from one to another, and I never saw him tied with either, only one got pregnant. Unfortunately not my girl and I don’t understand why? Could anyone give me an answer? I’ve been thinking everything you can imagine. I was so looking forward to seeing the babies she would have, she’s a black n tan except more like blonde n tan, the sire black. Will she get pregnant next time or…? Someone please give me an answer?

  10. Everything mentioned here is true to the T! I have two litter mates (both boys) they will be 12 soon. But one is misses the other more but he’s also the independent one which is interesting. They do fight with each other when they see other dogs. Don’t socialize well with dogs unless the dogs are super easy going and around their size. Training them was so hard because when I thought I saw progress one would fall out of line. But all that I wouldn’t trait it for the world they are my everything!!!

  11. A few months ago we went to adopt a young husky puppy. I was to pick out the one i wanted. I chose a young female. Just when I thought we were leaving. My grandfather (I live with my grandparents) decided to suddenly get a second one. A male. At first we had no issues. They would cuddle and play with one another. They have always slept separately. Been walked separately. I try to train them separately but often fail too. One was going to puppy class, with the idea of taking the other one after the first one was done her lessons.
    Then this virus thing happened and I have not been able to get them to socialize at all with others. I have a hard time calming them if anyone in my family drops by for something. It has gotten to the point that they were suddenly start fighting when they get too overly excited.
    Ever since they turned four months old (they are five now). They been constantly wrestling like they would when we first got them. I always allowed it because I read it is good for puppy play. But lately it has gotten out of hand. If it goes too far it can lead to a fight.
    I been working to try and get them to stop. But I can’t get their attention unless I use treats. My grandparents scold me for this saying they will fight just to get the treats. But I have tried everything. Clapping my hands. Ordering them by saying “Enough”, a whistle, You name it.
    I can’t just get in there and grab them because innocent play will suddenly become aggressive. My grandparents do that and it always leads to a fight.
    Any other time they cuddle with one another. Play with one another. They know basic commands like sit, wait and such. Only thing I have trouble with has been come, and heel and not getting them to immediately run out the front door or back door or jumping on other people which I am working on.
    I really do not want to get rid of any one of them. I love them both. I am hoping when they are fixed it might help a bit. But that won’t be till June. My stress level is getting to me. I just want them to get along more like they used too up until last month.

    1. I’m so sorry you’re in this position! It is normal for these behaviors to kick off as dogs begin to reach full maturity. Typically these issues are a combination of management and behavior modification, and the most intense fights we see are often sibling dogs. They play hard and they fight hard, and often one blends into the other. If we can be of assistance via online private instruction, please don’t hesitate to reach out.

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