What Happens When Dogs From the Same Litter Mate?

Breeding by Appearance or Pedigree vs. Genetics

• According to Dr. Carmen L. Battaglia, in a lecture from the Tufts Canine and Feline Breeding and Genetics Conference, "breeders have had to rely on their ability to recognize and associate names and titles with the traits and characteristics of each ancestor." As recently as a few decades ago, dog breeders would select two dogs solely based on similarly desirable appearance to produce their future generations of puppies. Alternatively, they would breed dogs with pedigrees and ancestors that were deemed desirable, whether in terms of "working" traits or for appearance. Today's breeders, however, also have access to genetic profiling and testing to ensure improved health in future generations of their chosen breeds.

Line Breeding, Inbreeding and Outcrossing

• According to the Dog Breeders Net website, line breeding is a "milder form of inbreeding," which is the "cornerstone of selective breeding." A breeder might choose to breed a grandsire and a granddaughter, for example, or an aunt to a nephew. Line breeding will "concentrate" the desirable or undesirable genes in the same manner that strict inbreeding will; however, it is a more gradual process than inbreeding.

  Inbreeding occurs when two very close relatives are bred together: mother to son, father to daughter, or littermates to each other.

  Outcrossing occurs when two apparently unrelated dogs are bred together. Because most breeds have a relatively small gene pool, an outcross might be considered breeding dogs unrelated within four, five or six generations.

Genetic Disease and Coefficient of Inbreeding (COI)

• The coefficient of inbreeding (COI) is a tool used to determine the probability that a particular gene came from a particular ancestor. As explained on Dog Breeders Net, two dogs that are completely unrelated would produce puppies with a COI of zero. However, a brother to sister mating would result in a COI of only 50 percent, not 100 percent, as might be expected, as long as the siblings' parents are unrelated. It would take many generations of brother to sister matings before the COI would reach 100 percent. Although it is best to keep as low a COI as possible, Dr. Battaglia explains that "can be beneficial and detrimental but it will not change or create new genes or undesirable genes. It will only expose those carried by the sire and dam through [making the genes more uniform]."

Breeding Littermates

• As can be seen above, then, nothing extraordinary will come from a single generation of breeding brother to sister. A slightly greater probability might exist for a birth defect or genetic issue to occur, should one already exist in the bloodline being refined; however, it is also possible that the converse would also be true. In the hands of an experienced and knowledgeable breeder, inbreeding can be a valuable tool that reveals the genetic flaws present in his or her stock, which then can be reduced or eliminated by selective line breeding.

The Truth about "Hybrid Vigor" in Dogs

• Because all breeds of dogs belong to the same species, true hybrid vigor does not exist when breeds are mixed. In fact, genetic health issues become more difficult to track and may appear unexpectedly in future generations. Donna Noland, writing for "The Dog Press," cites an article that identifies 102 genetic issues that can appear in mixed breed dogs. By way of example, if a collie that carries progressive retinal atrophy (PRA) and hip dysplasia breeds with a German shepherd dog that has a mild degree of hip dysplasia, those puppies will have a probability of carrying PRA. If siblings of the same litter mate, there is a probability that the puppies resulting from that breeding will then have a greater probability of actually having PRA, as well as displaying varying degrees of hip dysplasia. It is clear, then, that if any hybrid vigor exists in dogs at all, it has a very limited effect over time and, if inbreeding is present in a mixed breed dog population, that it can have the same deleterious effect that is found in inbred pedigreed dogs displaying varying degrees of hip dysplasia.