What is littermate syndrome? 

Littermate syndrome may occur when two puppies from the same litter are raised together. The siblings can become overly co-dependent, which takes a toll on each dog’s emotional development. This codependence makes it difficult for the dogs to bond with their new human parent. 

Puppies that experience littermate syndrome may also resist socialization. Since they have a deep bond with their sibling, they don’t feel the need to interact with other dogs. This can make regular interactions with dogs on walks, outings to the park, or vet visits difficult. 

When dogs develop littermate syndrome, they may experience separation anxiety when apart from their sibling. Anxiety in dogs can manifest in a lot of different ways – some minor and others more serious. Behavioral issues that stem from littermate syndrome may include: 

• Leash reactivity
• Rough play or fighting with their sibling
• Fear of strangers and other dogs 
• Chewing on household items 
• Fear of objects and sounds
• Biting, running, or barking when afraid

When does littermate syndrome develop?

Puppies are in their “socialization stage” when they’re between 3-12 weeks old. This is the time when dogs become more aware of their environment and relationship with humans. 

Harmony Diers is a vet tech at the Texas A&M School of Veterinary Medicine and Biomedical Sciences. She says littermate syndrome isn’t a given for puppies raised together and it isn’t specific to any breeds. But it is a risk without proper socialization. 

“Puppies ultimately learn how to react to things they encounter in the world during the socialization stage,” Dier says. “If bonded closely with their owner, an individual puppy will look to their owner for an answer on how they should react, either to be praised for appropriate reactions or to be redirected away from inappropriate ones.”

Littermate syndrome causes the puppy to look to their sibling for reaction cues instead of their human. When one dog is anxious or scared, the other will reflect that behavior. This can radicalize negative emotions in both dogs. 

In a healthy relationship, humans will let their dogs know what is and isn’t acceptable behavior. Dogs can understand our tone and body language to understand what gets them in trouble. 

But with littermate syndrome, both dogs are going to rely on each other too much to listen to their pet parent. This makes training and activities far more difficult for everyone involved. 

Can I prevent littermate syndrome?

With proper care, dog parents can prevent littermate syndrome altogether. The best option is to only raise one puppy at a time. This is the path of least resistance for both you and your new dog. 

Raising a well-behaved dog starts in puppyhood. The more individual time and attention you can give them, the easier it will be to train them. 

Taking in one puppy at a time doesn’t mean you can’t get more dogs in the future. Most vets recommend waiting at least 6 months between getting another puppy. It’s also a good amount of time to figure out if you even want another dog. 

If you already have two puppies, there are steps you can take to prevent littermate syndrome. You’ll want to have dedicated time with each puppy that separates them from their sibling. During crate training, the puppies should always be in separate crates, as well. 

Simultaneously practice obedience training with both dogs. But you’ll want to test run training separately in outings to the dog park, pet store, or vet. This gives each dog small bits of time to ease into behaving without relying on their sibling. 

My dogs have littermate syndrome. What should I do? 

If littermate syndrome has already set in, that’s okay too. The behavior can be fixed in most cases. Ask your vet for help and consider hiring a trainer that specializes in treating littermate syndrome.