When you live with a canine family, you know a dog's relationship to other pets in the household, such as son or daughter or brothers and sisters. Once your dog is grown, however, he doesn't think in those terms. Unlike people, domestic canines have no concept of incest. When dogs reach sexual maturity, they will breed with any intact dog available, even if it is a littermate or parent.
What Happens When Dogs From the Same Litter Mate?
Inbreeding and dogs
Some breeders practice inbreeding, which involves mating close relatives, including siblings, to produce certain characteristics. As Animal Wised puts it, this practice is "an irresponsible action with unpredictable consequences." However, they do make an admissible exception for the professional who has the expertise to weigh the pros and cons of such a mating. The truth is that most such breedings are conducted by the uninformed and unscrupulous, not the expert.
Breeders may also practice line breeding, which involves mating dogs who are less closely related, such as "uncles" and "nieces" or those sharing the same grandparent. Many purebred dogs, especially the less common breeds, come from relatively small gene pools. That means most puppies are related to each other within a few generations. Breeding Business recommends that dogs should not be bred to another canine with whom they share ancestors within four generations.
While those who practice line breeding do so to obtain certain traits in the litter, they should be aware they are rolling the genetic dice. Just as breeding litter mates to each other can result in puppies with the features they want, such as color or conformation, they are just as likely to end up with puppies having features they don't want. These include genetic deformities and predisposition to some diseases.
Even if the litter mates both look like happy, perfectly healthy dogs, that doesn't mean they don't carry genes that can cause serious defects in their offspring. The odds of such defects appearing in the litter increase exponentially compared to dogs that are out-crossed, or bred to a completely unrelated animal. Some of the health and temperament issues common in purebred dogs are related to inbreeding and line breeding for a "look" that causes unexpected side effects. This includes a compromised immune system, a higher prevalence of autoimmune diseases, lesser intelligence, and more aggressiveness.
A mother dog who is also the sister of her puppies' father has no idea about genetics. Her instincts will tell her whether any of her puppies are too weak or sickly to survive. Maternal rejection of puppies occurs for various reasons, but in many cases, the mother knows best when it comes to the odds of offspring survival. The breeder may have to make the decision whether to euthanize a sickly, inbred pup or commit to the arduous process of trying to save a puppy who is unlikely to ever prove healthy.
If you have puppies, you don't have to worry about them accidentally mating until they reach adolescence. Female puppies generally experience their first heat cycle at about the age of six months, while males reach sexual maturity by the age of nine months, according to the American Kennel Club. Giant breeds mature sexually later than small breeds. If you have a brother and sister pair in your home at that time, it's wise to have them neutered and spayed.
Even if you plan to breed one of your dogs in the future because it is an exceptional specimen, have the other one neutered to avoid an accidental mating. Otherwise, you and other family members must take special care to keep them separated when the female is in heat and able to breed. It just takes one mistake on someone's part for the two dogs to get together and possibly produce not only an accidental litter but a genetically problematic one.