Bringing home a puppy is a joyful, heartwarming experience. But what if you bring home two puppies? Or decide to add a second one shortly after the first? While it might seem like double the love and fun, raising two puppies together—especially of similar age—can lead to something called littermate syndrome.
This is why Itsie Bitsie Rescue does not adopt out littermates or puppies of similar age together. Please note that this does not apply to kittens!
🐾 What Is Littermate Syndrome?
Littermate syndrome refers to a set of behavioral issues that may develop when two puppies are raised together during their critical developmental stages. These puppies tend to form an intense bond with each other—often at the expense of bonding with their humans or learning essential social skills.
Common signs of littermate syndrome include:
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Separation anxiety when apart
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Fearfulness of unfamiliar people, dogs, or environments
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Difficulty focusing or learning during training
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Increased aggression between the dogs, especially as they mature
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Underdeveloped coping mechanisms
🚫 Do Puppies Have to Be Biological Littermates?
Not at all!
Littermate syndrome can occur between any two puppies close in age, especially those adopted within the same developmental window (typically under 6 months old). Whether they’re from the same litter, different litters, or even different breeds—it’s the closeness in age and shared environment that creates the risk.
🧠 Why Does It Happen?
During a puppy’s first year, their brains are forming the foundation for how they’ll interact with the world. If two puppies are raised together, they often become so reliant on one another that they fail to develop independence, confidence, or trust in humans.
Instead of learning how to explore, problem-solve, and adapt, they mirror each other’s behaviors—good and bad.
🐶 When Is a Puppy Considered “Mature”?
Most puppies reach emotional and social maturity between 12 and 18 months. Smaller breeds might mature a little faster, while large and giant breeds may take longer. Until this point, they’re still building the skills and resilience they’ll need for a lifetime of confidence and stability.
⏳ How Long Should You Wait Before Bringing Home a Second Puppy?
The ideal timing for adding a second puppy is to wait until your first puppy is at least 12 to 18 months old and well-trained.
By then, your first dog should:
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Be fully house-trained and understand household rules
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Have strong socialization skills and confidence
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Be able to focus and listen to you
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Serve as a positive influence for a younger puppy
Waiting gives you a better chance at raising two balanced, happy dogs—rather than managing a whirlwind of anxiety and chaos.
🛠️ Already Have Two Puppies? Here’s What You Can Do
If you’ve already brought two puppies into your home, don’t worry—it’s possible to avoid the worst effects of littermate syndrome, but you’ll need to be proactive and consistent.
Tips for managing two young pups:
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Train and walk them separately
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Crate them separately (even if in the same room)
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Spend individual time with each dog every day
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Enroll in separate training classes, if available
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Encourage independent play and exploration
The goal is to help each puppy build confidence and learn to interact with the world on their own—not just through their sibling.
🐕 Final Thoughts
While littermate syndrome isn’t guaranteed, it’s a real risk that can impact your dogs’ quality of life and your bond with them. Whether you’re bringing home your first pup or thinking about adding a second, timing and thoughtful training can make all the difference.
If you’re raising two pups or considering adding a second dog, reach out to a certified trainer or behaviorist right away. Every dog is unique, and expert guidance can help you create a solid foundation from the start.
📚 Sources & Further Reading
Penn State- Littermate Syndrome