"With all the hype the backyarders and Puppy millers try to put on their sites to sound reputable, be careful when it comes to them trying to explain their idea of how to breed or not breed. Many will try to slam ethical practice to try to justify their lack of purpose in their matings."

 

 LINEBREEDING A GOOD THING

... a very liberally edited version of "The Ins and Outs of Pedigree Analysis, Genetic Diversity, and Genetic Disease Control" by Jerold S. Bell, D.V.M. September 1992 American Kennel Club Gazette.

 

Without exception all breeds of dogs are the result of inbreeding.  Inbreeding has either occurred through natural selection among a small isolated population (i.e. the dingo) or through the influence of man breeding selected animals to derive specific traits.  Either way intensive inbreeding is responsible for setting enough of the dominant traits that the resulting group breeds true to type.  At which point a population of dogs can be said to be a breed.  

 

Dogs actually have more genes than humans.  Tens of thousands of genes interact to produce a single dog.  All genes are inherited in pairs, one from the sire and one from the dame.  If the inherited genes from both parents are identical they are said to be homozygous.  If the pair of inherited genes are not similar they are said to be heterozygous.  The gene pairs that make a Dachshund breed true to type are obviously homozygous.  However, variable gene pairs like those that control coat color, size, scenting ability, etc. are still heterozygous within the breed as a whole.

 

Linebreeding concentrates the genes of a specific ancestor or ancestors through their appearance multiple times in a pedigree.   When a specific ancestor appears more than once behind at least one animal on the sire's side and one animal on the dame's side homozygosity for that animal's traits greatly increases in their pups.  

 

However, if this specific ancestor appears only through a single offspring then the breeder is actually breeding on the offspring rather than the specific ancestor in question.   Having many "uncovered crosses" to a specific ancestor ( those that come through different offspring of this specific ancestor) gives the breeder the greatest chance of making the desired traits of the specific ancestor homozygous.  

 

Homozygosity greatly improves the chances that the resulting pups will in turn pass on the desired traits of the specific ancestor to their pups.  When selecting pups from a line breeding the breeder must choose pups that display the desired traits of the specific ancestor or they have accomplished little.   In fact, if these traits are not present in a linebred pup it is very likely that it inherited its genes from the remaining part of its pedigree and will be unable to breed true to type.

 

Inbreeding significantly increases homozygosity, and therefore uniformity within a litter.  One of the best methods of evaluating how successful a linebreeding has been is to gauge the similarity of the littermates as compared with pups of other litters with similar pedigrees.   Considerable similarity among littermates tells the breeder the genes have "nicked" or paired together as anticipated.  The resulting pups will likely be able to pass these genes to the next generation.

 

Undesirable recessive genes are always masked by a dominant gene.  Through inbreeding a rare recessive gene can be passed from a common ancestor on both the sire and the dame's side creating a homozygous recessive offspring.  The resulting offspring displays a trait neither of their parents displayed.  However, inbreeding does not create undesirable genes it simply increases the chance that traits which are already present in a heterozygous state within the breed will be displayed.

 

Too many breeders outcross as soon as an undesirable trait appears, blaming the problem on breeding "too close."  Nothing could be further from the truth.  In fact out-crossing insures that the undesirable trait will be carried generation after generation in a heterozygous recessive state only to rear it's ugly head again and again. Therefore they are simply passing a known problem on to succeeding generations.

 

When an undesirable trait is "unmasked" the breeder who does his breed a real service is the one that stays with his line long enough to rid it of the undesirable trait.  By controlling which specimens within their line are used for breeding in succeeding generations they can eliminate the undesirable trait.  Once the recessive gene is removed it can never again affect the breeder's line. Inbreeding doesn't cause good genes to mutate into bad genes, it merely increases the likelihood that they will be displayed.  

 

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The Inbreeding Coefficient (or Wrights coefficient) is an estimate of the percentage of all variable genes that are homozygous due to inheritance from common ancestors.  It is also the average chance that any single gene pair is homozygous due to inheritance from a common ancestor.  Our pedigrees display the Inbreeding Coefficient for each dog in the first four generations of a specific dog's ancestry.   Each Inbreeding Coefficient is calculated from that dog's 10 generation pedigree.

 

A  four generation pedigree containing some 28 unique ancestors for the 30 positions in the pedigree would likely generate a low inbreeding coefficient.  Yet a ten generation pedigree for the same dog might only have some 700 unique ancestors filling the 2048 positions in the pedigree resulting in a much higher and truer inbreeding coefficient.  Sometimes what appears to be an out-bred mix of genes in the first few generations (especially with owners naming their own puppies) ends up being a fine example of linebreeding.

 

It must be remembered that simply knowing the inbreeding coefficient does nothing to help us understand  which ancestors the dog is actually linebreed on.   To understand this, and to unlock the secrets of a dog's pedigree, we must do a homozygosity study.  The percent blood of immediate ancestors is relatively easy to estimate but not that important.  Homozygosity is far more important in determining what traits a dog is capable of passing on to it's offspring and extremely difficult to calculate with out the use of a computer.

 

On more than one occasion we have seen pedigrees in which the most influential ancestor for a homozygous trait doesn't even appear in the first three generations.  In this type of situation it is not unusual this particular ancestor to contribute over 25% of the homozygous genes of the dog in question.  It is of paramount importance for the dedicated breeder to know not only the percent blood but the inbreeding coefficient for the resulting litter before the mating is done.

 

Too many breedings are made solely upon the basis of appearance  with little regard to the sire's and dame's respective pedigrees.  Individual dogs may share desirable traits but inherit them differently.  This is especially true of polygenic traits, such as ear set, bite, or length of forearm.  Many breeders fail to understand that breeding dogs that are phenotypic ally similar but genotypic ally unrelated  won't necessarily reproduce the desired traits and in fact many even reduce the chance of these traits being reproducible in the next generation. 

 

Conversely, individuals with the same pedigree do not inherit exactly the same genes and will not breed identically. Therefore all linebreedings must be made on a combination of performance, appearance and ancestry.  If a breeder is going to be successful in solidifying a certain trait they must rigorously select specimens  which display the desired trait and have a similar pedigree.  In so doing breeders have a chance of making the desired trait homozygous over time.  This is the key to successful linebreeding that is most often missed by unsuccessful breeders.

 

In choosing a line of dogs to breed it is wise to choose a line with "critical mass".  A line in which the most prepotent individual was mated many times and produced many superior offspring.   Without enough genetic diversity it will be difficult to find animals that do not also share the faults of the most prepotent individual.  These will be faults the breeder will have the most difficulty in eliminating. No matter how limited the critical mass the breeder must never breed animals that are poor examples of what they are trying to reproduce simply because they share common ancestors.

 

Every breeder is fighting "the drag of the breed," which is the tendency for all animals to breed toward mediocrity. Unsuccessful breeders overlook an animal that has a great trait because it also has a minor fault in favor of an animal that has no faults but no great traits.  Successful breeders use specimens within their line that have at least one truly great trait and breed them  with specimens that in turn are great where the other dog is weak.  In so doing it is possible to linebreed offspring that are better than both the sire and the dame, which in turn can pass the great traits on to the next generation.

 

The perceived problem of a limited gene pool in pure bred dogs has caused some "experts" to advocate out-breeding of all dogs.  Studies in genetic conservation of rare breeds have shown this practice actually contributes to the loss of genetic diversity.  If we were to uniformly out-cross all "lines" in a breed we would eliminate the differences between them and therefore the diversity between individuals within the breed.   The process of breeding the genetic purity of any line of Dachshunds will in fact contribute to genetic diversity within the breed itself.

 

Those who argue against linebreeding are inevitably those who have never successfully bred animals themselves.  The main argument advanced by these "know-nothings" is that out-crossing is in and of itself good because it produces hybrid vigor.  If out-cross breeding is the answer why don't owners of successful herds of Holstein milk cows ( who's livelihoods depend upon the health and performance of their cows) out-cross to the American Shorthorn milk cow?  Obviously, they don't because they would go broke with the resulting animals.  Hybrid vigor is never in and of itself the answer.

 

In fact, even when out-crossing does produce the desired hybrid vigor the resulting "superior specimens" of the F-1 generation most often can't reproduce themselves. Then  what has been accomplished by even a successful out-breeding?  Those who advocate out-crossing dogs are effectively proposing that hunters entrust the development of their performance dogs to the whims of random chance.  If you believe this is a wise course then you should locate another breeder.  May we suggest you check the want ads of your local newspaper where you will find many splendid examples of out-cross breeding.

 

Successful linebreeding is a long and arduous task; one that requires a lifetime's commitment to a particular line of dogs.  We have great respect for the few breeders  who successfully developed and perpetuated a particular line in the past.  Even if we don't have a single dog from their line in our pedigrees we have studied their breeding patterns and, over the years, developed a deep appreciation for their work. 

 

Breeding true to type - breeding true to the breed  

 

"With all the hype the backyarders and Puppy millers try to put on their sites to sound reputable, be careful when it comes to them trying to explain their idea of how to breed or not breed. Many will try to slam ethical practice to try to justify their lack of purpose in their matings."