At Bydand, we have always believed that the way to produce consistent quality is by selective linebreeding, and we have employed it as a breeding system successfully for many years.
(At right is a Bydand Silk displaying the results of a classic Brackett's Formula linebreeding. Predictably, this dog strongly resembles the dog off whom he was linebred.)
Because lot of people do not understand linebreeding, we thought we’d explain it in some depth for those interested in learning more about it.
| |
The best way to begin is by defining the terms as used by breeders:
Inbreeding is a systematic program of breeding closely-related animals- to breeders, this generally refers to father/daughter, mother/son, and full sibling matings.
Linebreeding is a term used only in animal husbandry to describe a less- intense program of inbreeding- usually uncle/niece and half-sibling matings. In breeders’ terms, one linebreeds off a specific animal, and that particular animal may show up multiple times in a pedigree.
Outcrossing is specifically the breeding of two unrelated inbred strains within the same breed, and typically produces hybrid vigor (in what geneticists refer to as the F1, or first-generation, hybrids), but the resulting animals generally do not reproduce themselves with any consistency, unless bred back into one of the original strains.
Outbreeding is the repeated breeding of unrelated animals, with no common ancestors for several generations in their pedigrees, and cannot really be classified as a breeding system, although it is widely used by both novices and commercial breeders.
Hybridization in dogs generally refers to the deliberate crossing of two different breeds. This typically produces heterosis, or "hybrid vigor", where the average performance of the hybrid exceeds that of either parent breed. A first-generation hybrid is called an F1. An F1b is the result of a backcross of an F1 hybrid with a dog from one of the original "parent" breeds. An F2 hybrid is the result of a pairing of two F1 animals.
A lot of people are frightened by the terms linebreeding and inbreeding, and assume that the use of these breeding systems inevitably results in genetic problems.
In fact, the opposite is often true. By utilizing selective inbreeding, lines can be developed that are genetically free of undesirable recessive traits. Constant outbreeding, on the other hand, produces a situation where those genes remain hidden until they are widely dispersed throughout the population, at which point animals displaying the undesirable trait begin to appear everywhere in the breed, and there is little hope of selecting away from it.
Breeds that become extremely popular in a short time often fall prey to widespread health and temperament problems, and it is usually erroneously blamed on "too much inbreeding", when in fact it is usually a result of constant outbreeding, with little or no health screening performed on the breeding stock.
So why has inbreeding, and its less intense form, linebreeding, gotten such a bad rap?
It’s simple. We are a society with a strong social taboo against incest, and we carry this taboo over into our feelings about animals. Nature, on the other hand, has no such reservations, and many wild populations are by definition inbred (especially in species with strong social orders) as generally only the dominant males breed.
What about inbreeding depression? In other words, how long can one inbreed before the bottom falls out? Geneticists have studied this both in the wild and in laboratory experiments, and reviews, as they say, are mixed at best. Among the genetics community, one will find both proponents and opponents of inbreeding arguing their case with equal vigor.
However, it is interesting to note that historically, many cultures have practiced inbreeding with no evidence of genetic degeneration. Although not alone in the tradition (incestuous marriage was also common under Greek and Roman rule) the most famous were certainly the ancient Egyptians. During the Ptolemy Dynasty, which ruled Egypt during much of its heyday, deliberate inbreeding was common practice among both royalty and commoners alike- examinations of 161 marriage records of commoners in the Ptolemic period reveal that 24% were among siblings. And, astonishingly, every Pharoah from Ptolemy II to Ptolemy XII was the product of a brother/sister marriage!
|
What was the result of this?
Cleopatra, who ruled Egypt for twenty-one years during extremely rocky political times, was the product of nearly three hundred years of brother/sister marriages. (323B.C.- 51 B.C.)
Historical records reveal her to have been both extremely beautiful and highly intelligent, with a gift for languages- she was fluent in several.
Cleopatra also managed to seduce not one, but two, Roman Emperors in succession, producing children by both of them and thereby ensuring the political security of Egypt.
Any suggestion of "inbreeding infertility" is dispelled by the fact that Cleopatra was herself one of five children born to Ptolemy XII and his wife, and she produced several children herself.
| |
In the face of that evidence, one wonders how so much negativity has come to surround the practice of inbreeding in domestic animals.
Well, several other cultures had less luck with the practice of inbreeding - most notably among the royalty of Spain and England - where genetic anomalies like hemophaelia and polydactyly abounded.
Inbreeding, man has discovered the hard way, is indeed a double-edged sword.
Inbreeding cannot, in of itself, CREATE genetic anomalies. Genes are genes, and unless they mutate, they are simply passed from one generation to the next, in either a recessive or dominant manner. Whether a gene is inherited from a close relative or a perfect stranger does not affect its ability to do its job.
What inbreeding can do is increase homozygosity, (where each gene pair at a given locus contains identical alleles of the gene) and if those alleles are deleterious, a recessive anomaly will present itself. Inbreeding does not so much create genetic problems, then, as reveal them, especially recessive ones which would otherwise remain hidden, and therefore be passed unknowingly to successive generations.
But it is also important to remember that not all recessive traits are deleterious, and desired traits known to be recessive can be locked in just as surely by inbreeding.
|
One such trait is the G pairing, a simple color gene allele that causes a dog to silver out at maturity, and common in this breed. (This mutation is not, in of itself, known to be deleterious, unless one wishes to breed dogs who keep the color they are born with, instead of fading out at maturity, which is common in Silks, and often a disappointment to the owner.)
Its recessive allele, g, causes the animal to maintain its early rich color, and probably represents the original gene at that locus, with G (the so-called "silvering gene") having emerged as an incompletely dominant mutation.
|
A black dog who does not silver is homozygous (pure) for gg, and does not have the dominant silvering allele in his DNA to pass on. (If he has even a single copy, he would display it, because that is what dominant means.)
So in this case, assuming we wish to breed dogs that do not silver, this "recessive gene" would be desirable.
|
Many of the traits that we considerable desirable in purebred dogs- indeed, many of which determine breed type- are controlled by recessive genes rather than dominant ones.
Good breeders have long known that the genes that produce proper shoulder layback (which gives Silks that desirable long arched neck and high head carriage) are recessive to those that result in straighter shoulders and a short neck, for example.
And, the only reliable way to cement these genes into a line and produce animals who display them with consistency, is by inbreeding, or linebreeding (which is slower but somewhat less risky.)
What are the risks?
Well, unlike the gene that prevents a dog from silvering, or those that produce good shoulder layback, many recessive genes cannot be seen with the naked eye, and many are not as desirable.
By linebreeding, many of those genes, if present in the genotype of the original stock, will turn up as unpleasant surprises within the first generation or two. Rigorous selection must be practiced in order to linebreed successfully, and this requires a thoroughly objective eye and a willingness to health screen both the breeding stock and the offspring produced.
If selection is rigorously applied, however, a linebred strain can be consistently healthier, sounder and certainly more attractive than its outbred counterparts.
In the game of breeding, selectively linebreeding from superior animals is like playing poker with a stacked deck and a couple of Aces up your sleeve…it ups your odds of coming out on top.
Outbreeding, on the other hand, is all too often more like playing 52 Pickup.
In case this hasn’t occurred to you yet, a true passion for breeding good dogs is a lot like a compulsion to gamble, only more expensive….passionate breeders are always hoping the next hand is going to be a winner.
That’s why we do it.
|
copyright 2011 Bydand Havana Silk Dogs
All material contained on this website is protected under Federal copyright law
and may not be reproduced wholly or in part.
Permission to link to this website may be granted upon request.
|
|
