While littermates may play and live with each other quite happily while they are very young, the idea that they will look after and entertain each other for their whole lives is a dangerous one for several reasons. Firstly, raising littermates together past the age of 8 weeks can cause serious dependency issues.
Professional trainers like myself recommend against bringing home two puppies around the same age, let alone two from the same litter. While this sounds like a good plan in theory, in practice it often causes quite a bit of heartache and potentially some serious aggression trouble.
Dunbar agrees that it's often best to separate littermates, especially if symptoms appear early, so that each has a chance to develop normally as an individual.
Sticking Together Might Not Actually Be a Good Thing
But far from causing them pain, some pet behaviorists argue that separating dog siblings is the better choice. Dogs that spend their whole lives together can become fixated on each other and develop behavioral issues.
Many breeders recommend that your first dog be at least one-to-two-years old before you add a second to the family.
The 'Rule of Three' means that you can gauge the time it might take for your dog to fully acclimate to his home in threes: three days, three weeks, and three months. Think of your new dog's first 3 days as their time to decompress as they transition from a shelter or foster home into your home.
What exactly is “littermate syndrome” and is it real? Littermate syndrome can occur when two puppies adopted from the same litter grow up together in the same home. In some cases, these sibling puppies form such a deep bond with each other that they fail to properly socialize with people and other dogs.
Dogs are social animals and usually happier around other dogs, but a second dog will never be a substitute for inattentive, absent or too busy owners.
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.
Dogs are inherently social animals that live well together in groups, but that does not mean that all dogs get along. Most dogs will welcome a new sibling, but it is not always smooth sailing. The furry family member you have now will face many changes when a new dog enters the picture and may feel a bit displaced.
So in short – yes, puppies miss their siblings at first. But they quickly get over it. Dogs don't really have the mental capacity to reflect on their early-life peers, so they won't really “miss” their siblings in the way a human might.
“Dogs don't necessarily know that another dog in their life has died, but they know that individual is missing,” says Dr. Marc Bekoff, professor emeritus of ecology and evolutionary biology at the University of Colorado Boulder and author of the 2018 book Canine Confidential: Why Dogs Do What They Do.
There's no set timeline for how long this takes, but it can take over a year before unbonded littermates can be trained together. Your co-dependent pair may need more time. Beyond teaching them to be apart and training them individually, it's essential to approach each dog as a separate dog.
It is theoretically possible to prevent littermate syndrome by doing things like taking the dogs for separate walks, enrolling them in separate training classes, and setting up separate playtime for each with their pet parents. You can already see that's a lot of extra work for the new owner.
Effective communication between the dogs is the key to harmony (see Using Punishment Effectively, Why Punishment Should Be Avoided, and Canine Communication – Interpreting Dog Language). Instead, if you can see that the dogs are about to fight, the dogs should be called, redirected or encouraged to do something else.
Fights between puppies are often a result of overstimulation, which can quickly happen with two puppies living under the same roof. This behavior tends to be particularly true for littermates of the same sex.
The ideal minimum time that the puppy should be able to separate from its mother is 8 weeks. Still, many ethologists also claim that the puppy should be with its mother until 12 weeks of age. We must point out that the longer a puppy is with its mother, the better its development.
Before settling on a breed, think about the gender of the dog. For the happiest dogs and the safest household, opposite sex dogs almost always do best together. Many same-sex combinations of dogs will fight, sometimes to the death. Those who work out a dominance order may not fare much better.
Many people are hesitant to adopt a second dog because they assume it will be twice the work and twice the money. But the truth is, owning two dogs doesn't have to be more work – in fact, it can often be easier. And as for the cost, it will cost more money than one but not twice the amount.
Most experts agree that, as a rule, male and female dogs get along better than two females or two males.
In both humans and dogs this is caused sibling rivalry. Sibling rivalry occurs when two dogs living in the same household fight repeatedly and aggressively. It may start with snarls or growls, but can then progress to vicious, prolonged fights.
Littermate syndrome can affect dogs of any breed, and it may also affect unrelated puppies who are adopted at the same time and raised together. The good news: not all puppy pairs develop littermate syndrome and pet parents can prevent significant issues with specialized training methods.