Inbreeding Among Dogs

Breed Profile

Dog

Bull Terrier

  • WEIGHT: 45 to 65 lbs
  • HEIGHT: 21 to 22 inches
  • COLOR(S): White, brindle, any color with white markings on head.
  • BREED GROUP: Terrier
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The Dangers of Inbreeding Among Dogs

The Dangers of Inbreeding Among Dogs

by Jack Russell  

Inbreeding consists of mating closely related couples of the same species, such as mother-to-son, father-to-daughter, and sibling-to-sibling. This practice can cause problems for breeders who intend to mate dogs for commercial reasons, such as exhibitions, sports, and selling litters to potential owners. Stud and offspring services seek after nearly flawless litters for winning the approval of judges; however, inbreeding spreads deleterious genes causing the breed to lose its vigor. Laboratory animal suppliers may use this to their advantage in order to create breeds that have a depressed immune system prone to specific diseases. Controlled inbreeding may also be used to fix desirable traits, such as aggressiveness, lean-to-fat ratios, and growth rate, a process known as line breeding.


Naturally occurring inbreeding in the wild can transfer widespread deleterious genes within a species of a geographical region. If left uncontrolled, this can become noticeable in later generations as future offspring inherit these genes. Scientists have discovered that wolves have genetic similarities between each member of the pack, even if they live in different regions. Many researchers have theorized that the destruction of their natural habitat may have drastically reduced wolf population numbers; therefore, creating a genetic bottleneck within the species. As a result, wolves have become susceptible to an array of diseases, because of their lack of genetic diversity. Rare cases of extreme inbreeding severely affect the reproductive success among small litters, and increase the rate of mortality among each pack of interbred wolves. Scientists hope to develop a more varied wolf gene pool by introducing other pack members from distant geographical regions. The ultimate result of continued inbreeding among wolves is perpetual loss of vigor and probable extinction of the species through contracted genetic pools, decrease in fertility rates, and increased abnormality and mortality.


Selective Breeding
Selective breeding, or the process of creating a new breed from a desirable genetic mutation, typically leads to frequent mating between related dogs. Some breeds originated from spontaneous mutations, which have posed an array of problems for newly created breeds. For instance, German Shepherds have a recurrence of hip dysplasia and achalasia, while other breeds suffer from more common maladies, such as patella luxation. Bulldogs suffer from breathing problems, whereas Dalmatians have become prone to deafness. Increased frequencies of diseases in certain breeds indicates that faulty genetics were passed down via inbreeding; however, researchers have found the solution and determination to preserve a species from interbred generations using a process known as outcrossing.


Outcrossing of Breeds
Wildlife conservations, zoos, and private individuals involved in animal husbandry may network and participate in captive breeding programs to outcross their own stock with other purebred collections. Outcrossing involves selecting a male and female mate from the same species, yet from a different geographical region, to reverse broaden the differences in the gene pool. Outcross breeders typically borrow animals from each other in order to achieve genetic diversity while mating their animals to produce a future line of purebred offspring. Outcrossing attempts to reverse the damaging effects of inbreeding, whereas line breeders use methods to preserve or change a specific trait of a species. This may not always work in accordance with the breeder's desire. For instance, many line breeders have attempted to change the appearance of a Pug's face to a flatter and rounder head, resulting in required C-sections and congenital birth problems. Some breeds have lost their ability to give birth without human assistance.


Preservation of Traits
In the past, breeders wanted to focus on preserving hereditary strengths and eliminating current weaknesses. A certain number of breeds did not respond well to line breeding methods. To better clarify, some breeds responded well to improving the strength of the breed; however, it also caused the formation of genes detrimental to the dog's health. Nowadays, breeders have re-prioritized their intentions of line breeding based on its usefulness. Introducing a new breed with a genetic crossing of an unrelated breed will usually change the character of the breed being preserved. Some cases of progeny require six to eight successive generations before the offspring becomes purebred in relation to its ancestors. Breeds that have a natural difficulty in producing genetic variability find themselves endangered of becoming extinct unless humans intervene by outcrossing between genetic lines.

Dog breeders have the opportunity to ensure vigor in future litters if they commit to eliminating inbreeding and using outcrossing methods where permissible. Outcrossing can prevent a breed from stagnating with the introduction of “new blood” within the gene pool. In addition, dog breeders should select another mate with desirable traits, preferably distant relatives. Dog breeders should steer clear of mates with signs of low fertility, high mortality rates in puppy litters, and loss of immune system diversity. For instance, if nearly fifty percent of a litter dies from a simple infection, then breeders should not select a mate from that specific litter for future outcrossing. Physical abnormalities, such as misaligned jaws and nine toes, indicate that the litter has a long history of interbred descendants.

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