The Truth About Littermate Syndrome: Why Adopting Sibling Puppies is a Bad Idea
When it comes to adopting a new puppy, it can be difficult to choose just one. Many people think, "Why not adopt two?" After all, they’ll have a playmate, right? Unfortunately, adopting sibling puppies can lead to a well-documented behavioral issue known as littermate syndrome—and it can cause serious problems down the road.
What is Littermate Syndrome?
Littermate syndrome occurs when two puppies from the same litter (or even a parent and offspring) grow up together and develop unhealthy dependencies and behavioral issues. This isn’t just about minor sibling squabbles; these dogs can end up in serious, often violent fights. One dog will typically become dominant, and the other submissive, but in many cases, both will compete for leadership, resulting in aggressive behavior. These fights can escalate to the point where one or both dogs must be rehomed or even euthanized.
Why Does Littermate Syndrome Happen?
Dogs, like people, have individual personalities that need space to develop. When two littermates are raised together, they often fail to form strong bonds with their human families. Instead, they rely on each other for emotional support and leadership, which can lead to fear, aggression, and extreme codependency. This makes training difficult because they look to each other instead of their human for guidance. As they mature, conflicts often arise, and fights can become increasingly dangerous.
Real-Life Cases
At Motley Zoo Animal Rescue, we frequently hear from people who unknowingly adopted sibling puppies and now find themselves in crisis when the dogs begin fighting at around nine months old. A classic case involved a family that purchased two Boston Terrier siblings on a breeder’s advice. As the dogs matured, they started fighting so severely that they needed muzzles even during training. Eventually, the family was forced to rehome one of the dogs.
While there are rare exceptions, such as a case where a puppy with neurological issues bonded with his sibling, these situations are uncommon. The general rule? Avoid adopting siblings.
How to Prevent Littermate Syndrome
If you have already adopted sibling puppies, or if you are fostering multiple puppies, early intervention is key. Here’s what you can do:
Separate Training – Each dog needs individual training sessions to develop confidence and obedience separately.
Separate Walks & Playtime – Take them on individual walks and ensure they spend time apart so they do not become codependent.
Crate Separately – Each dog should have their own crate and sleeping space.
Encourage Individual Bonding – Make sure each dog has one-on-one time with you to strengthen their human bond.
Watch for Signs of Aggression – If you notice one dog constantly overpowering the other, intervene before fights escalate.
Why You Should Wait to Add a Second Dog
The best way to have multiple dogs in a household is to adopt one, train and socialize them well, and then introduce a second dog when the first is around two years old. By then, your first dog will be well-adjusted and can help teach appropriate behaviors to the newcomer.
What About Cats?
Interestingly, the opposite is true for kittens. Cats do better when adopted in pairs because single kittens often develop behavioral issues due to a lack of socialization. Kittens raised alone tend to be more aggressive, biting and scratching their owners because they don’t have a playmate to teach them boundaries. This is sometimes referred to as “single kitten syndrome” or “Tarzan syndrome.”
Final Thoughts
When adopting a pet, it’s important to set them up for success. While it may seem kind-hearted to take two puppies together, it often leads to heartache and behavioral challenges. Instead, focus on raising one well-trained, well-socialized dog, and consider adding another only when the time is right.
If you’re experiencing littermate syndrome and need guidance, reach out to Motley Zoo Animal Rescue and check out our podcast on this subject!
Rock on. Rescue on.
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