But then I heard about something called littermate syndrome. According to The Bark, littermate syndrome occurs when two puppies' deep bond impairs their ability to grasp the nuances of both canine-canine and human-canine interaction. While the evidence is anecdotal, many trainers, behaviorists and breeders acknowledge that it's real.
Puppies with littermate syndrome depend on one another and tend to ignore their owners entirely when presented with the option of paying attention to one another — as if the humans aren't in the room. They may also be fearful of unfamiliar people or dogs and even just situations or stimuli they're not familiar with. They may even fight incessantly.
Tena Parker, certified professional dog trainer with Success Just Clicks Dog Training in Pittsburgh, Pennsylvania, says the name can be deceiving. "Two dogs who are adopted/purchased at/around the same time can absolutely display concerning behaviors attributed to littermate syndrome, regardless of age." So it's not just puppies you need to worry about.
While the sex of the dogs doesn't seem to affect whether littermate syndrome will happen, Parker notes that some breeds do have a propensity for more same-sex aggression. She also warns that a lack of symptoms up front doesn't mean fighting won't eventually happen. She's had clients whose dogs might scuffle from time to time, but everything was fine until an all-out brawl broke out after sexual maturity.
Typically, Parker says, littermate syndrome fighting manifests as one dog being more confident and the other being more submissive. These dogs have an unhealthy attachment. It may seem like innocent puppy play at first, and they may seem like they love each other most of the time, but eventually, the more confident dog may become an outright bully. It'll guard things like food and toys or even push the more submissive dog away from attention. Parker notes this can create a very stressful environment for the more submissive dog. It's likely not surprising to the humans reading this that the submissive dog then tends to cling to the more confident dog even more.
No. Littermate syndrome can be avoided (note the italics on can). First, you can't ignore the warning signs. Just because it doesn't seem that bad now doesn't mean you shouldn't take it seriously. Taking it seriously may be the very thing that prevents it from getting out of control. Given what the preventative measures are, the worst that can happen if you're wrong… is that you're wrong.
If it develops, you have a much harder road ahead that will likely mean lots of stress for you and potentially (if not probably) re-homing one of your pups.
Your dogs need to learn to spend time away from one another. Separate feedings, separate beds or crates, separate training, socialization with other dogs and humans. That doesn't mean you have to quarantine them from one another for a year, just that they need to learn normal interactions with humans and dogs, which may (probably does) require them to be apart.
Since I've had the issue myself, I asked Parker about taking treats away when the more confident dog takes them from the submissive pup. She advises against it because it might cause the dog to guard its treats from the human (which can be a problem if your dog gets something it isn't supposed to have). If it becomes a problem, she says to give them treats separately.
Owners might also have issues with aggressive play, especially with puppies. Parker says, "I always suggest owners modifying play that they are not comfortable with — if it makes them nervous, interrupting the play and slowing things down isn't a bad thing. That being said, I try not to interrupt play that is appropriate, though perhaps rowdy, because I want to let them do some good communicating."
How do you know? "One way to 'check in' with the dogs to see if the play is still mutual is to calmly restrain the aggressor," she advises. "If the other dog comes back for more, it was likely mutual play. I would do everything in my power to not allow them to rehearse any behavior that I felt could easily switch into a fight."
If you have sibling (or even non-sibling) dogs you believe may have littermate syndrome, it's probably a good idea to get the help of a professional trainer or behaviorist as soon as possible.
And always remember that you can't assume all is lost because there's a thing called "littermate syndrome." All the hard work you might have to do pays off if you're willing to do it.
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