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Introducing the Breed Value Assessment (Zuchtwert Schätzung) © 5 Feb 99 Translation by Fred Lanting from the July 1998 SV Zeitung - edited by Bobbie Impellizzeri |
Herr Doktor Reiner Beuing writes -
In its general meeting in May 1998 in Leipzig, the SV unanimously agreed upon the introduction of the Zuchtwert evaluation (Breed Value Assessment). At the same time, it was agreed to publish this knowledge for a breeding program for the fight against hip dysplasia. With this, the SV takes the first step on an untrodden path. In the presentation of this, it naturally has been planned conscientiously and thoroughly by the committees of the breed control and the technical sections of the headquarters; nevertheless it remains next for the practical breeder to go along this path and to trust it is the right path. In these pages, I would like to help create trust. One should first clarify the desire (need for) a Zuchtwert Schätzung (Breed Value Assessment).
There is an old saying animals do not always reproduce what they themselves are. These sayings come from breeders and I am almost ashamed to call this trivial statement "breed wisdom". It is routine in breeding kennels' experience that many a show winner, performance star, champion and typey dog produces disappointingly, while on the other hand, out of almost mistaken, mediocre breedings, that dreamed-of breeding success arises.
Similarly, one must understand that a healthy dog is no guarantee that his progeny are healthy. HD, elbow dysplasia, epilepsy, eye disorders, etc. unexpectedly arise from mostly normal parents, and catch most breeders unawares. If, however, it is true that the breeding animal's (parent's) heritable characteristics can be different from that of its performance (offspring), one must wonder, why then all these breed regulations (surveys and breeding prerequisites) based on what the dog IS, instead of building a model which can tell us how the dogs will probably produce.
This contradiction is that, almost intuitively, one consciously tries to include the already available information concerning the siblings, and his own experience with the progeny. No breeder can put forward a really objective picture, however. Individual cases can be too drastically positive as well as negative. Additionally, there is the sheer number of German Shepherd Dogs and no individual is in the position of getting and cataloging their achievement tests or health control data, at over 30,000 puppies annually.
So up to now it remained to consider only the stud dog or the breeding bitch itself. Today however the time is ripe for more. Computer technology and the information revolution have matured so that the club can document not only all members, but also can give instruction regarding how the dogs themselves are, and how they will probably produce.
We have numbers that tell us what the animals are like. For instance, the score described at the tracking work tells us whether the dog was good or bad. We have numbers about the size (shoulder height) and points on gait or type. For each feature there is a numerical value which tells us how pronounced the characteristic is.
As breeders, however, we need a number which tells us how pronounced the feature in the progeny will be. This number, to be applied to the breed, is called Zuchtwert (breed value). There is, therefore, for each feature, one phenotypic measurement and one genetic breed value. As concerns HD, as first and unquestionably the most urgent trait in the SV, a breed value is to be published in the future.
Definition of the breed value
Using
the preceding explanation, the definition of the breed value easily becomes
understandable:
The
breed value is a numerical value to be applied to the breed. It describes
which effect the genes of an animal have on a characteristic, if these
are combined with the genes of the rest of the population and normal environments.
It is to be emphasized first of all that the breed value has nothing to do with how valuable or worthless a dog is, but is only a numerical value with a description that should tell us if the genes working on this trait strengthen or weaken it. For diseases, that means that high breed values indicate a worsening of what the breeders see as undesirable regarding the disease or construction. The goal must be to introduce breeding animals that reduce the disease risk in the breed. Low numbers are therefore more valuable in this case!
With other traits we take as being prized, or what one wishes, high breed values indicate outstanding predisposition for high drives. "High" is therefore called valuable here!
With the shoulder height, it is not that simple. A high breed value for a dog in this instance means that his genes increase the size. That can be valuable and important for a small bitch. For a bitch already over the limit, such a dog is not recommended. It remains for the judgement of the breeder to select the suitable dogs for his bitch, if he first knows what the breed values are.
The relative breed value:
If one is to advertise or publish breed values, they must be easily understood. An HD breed value of +0.14 means for example, that with an equivalently-rated partner, the offspring probably will be 0.14 (HD degrees or points) higher. This is not easily understood; therefore, breed values are not expressed as absolute numbers, but as relative to the breed cross-section. Thereby one takes 100 (points) for the breed level (typical average). Dogs with ZW over 100 increase (worsen), while those under 100 reduce the attribute. The variation from the median (standard deviation?) amounts to +/- 10 points. Thus, if a bitch has a breed value of 95 for HD, one knows that she can improve the breed, but a dog with ZW of 115 exacerbates the HD problems.
By referring to breed averages, the classifications regarding different characteristics also become comparable. If we get, for example, a dog with HD 92 and shoulder height 108, this makes it clear that he is a breeding partner that can be used for improving the HD scores and increasing the inherited size trait.
Why is breed value median always only an estimate?
One finds, in the biology of inheritance, that we can determine the true breed value only with difficulty. The owner's personal judgement of the animals is no 100-percent reflection of the genes; therefore the proposed use of breed values, although the genes will doubtlessly control the life functions.
1.
The genes work only in the particular individuals themselves and not in
concert with the genes in the rest of the population (there can be, for
example, action of concealed recessive genes that do not show in others).
2.
Environment certainly influences the expression of the genes in these animals.
Both reasons (for ZW being only an estimate) give a false picture. The reliability with which one can recognize the true breed value from the appearance (phenotype) is, for instance, around 20% for HD, for shoulder height around 50%, etc. One calls this percentage heredity and/or heritability.
Each animal receives his genes from father and mother, half from each one at random. Information about siblings or progeny are thus based only on a random gene sample from the contribution of the parents. First, the statistics allow us to get an approximate picture from abundant knowledge and/or observations. A spoonful from the stock pot only gives only a chance picture as to how many "chunks" and how much "broth" are in the soup, and each additional ladle shows us more accurately how rich the soup is. So also our knowledge about the genetic "capacity" of a breeding animal increases with each additional offspring.
Present Standing of the Knowledge
Breed values must be available at each point in time to help decide many things: whether to apply a stud dog to a given bitch, a breed survey, a puppy sale, if the puppy should become a breed dog, and yes, even already before birth, since the question is put as to whether subsequent puppies are themselves framed for life by their genetic portion.
All available information must be processed and constantly brought up to date, to bring together the knowledge needed to make an estimated breed value. Estimated breed value means " the most probable genetic production, as determined by the current knowledge". Since in the course of time more knowledge is always forthcoming, certain limitations of the breed value estimates will also change.
First level of knowledge
From father and mother, we can make some statements about what genetic contributions may exist, by means of their breed value assessments. Since father and mother each bring in respectively half of the genes in each of the puppies, and the effect of these genes is described by the breed value, then for the calculating of breed value estimates of the puppies, it must be 1/2 the sire's breed value plus 1/2 the dam's breed value. These decisive points are thus supplied to you at the time of the mating. The better the breed values of the parents are, the more favorable is the probable genetic make-up (breed value) of the puppies!
Second level of knowledge
While one can learn during the gestation of a bitch, and actually even before the actual mating, dogs can also be evaluated from data on earlier litters of these parents. These siblings can improve the evidence about father or mother and their "progeny-correcting" breed values. Thereby, breed values for individual puppies can be known somewhat, without physically evaluating the puppies themselves.
Third level of knowledge
Up until now, the level of knowledge was derived only from the breed values of the parents, which become increasingly more accurate. Since all puppies of a litter have the same parents, all puppies must also have equal estimated breed values.
Each puppy however has received respectively half from the father's and half from the mother's genomes. By sheer good fortune, a puppy thus can have received more favorable working genes than his littermates. This "distribution of good luck" or "distribution of bad luck" at the stage of cell combination and development of the egg and sperm leads to the fact that full siblings can considerably differ genetically in their particulars.
Whether an individual animal is blessed or punished by the random allocation, for instance in reference to the HD genes, can be estimated only if the animals are x-rayed for HD. Since the picture depends on "egg contribution" and also on environmental factors, radiography technique, position and judgment, it consists solely of knowledge derived from the ancestry. The breed value of the feature changes more or less drastically according to heredity at this point in time.
Fourth level of knowledge
If full siblings also get evaluated, and most are assessed quite close to the time that the animal of interest (called the "Proband" or "probationer") is under consideration, then their "declarations" supplement the breed values of the parents and also, indirectly, the breed value of the "probationer". Breed values thus can change further after a individual appraisal, even if a dog is not used in the breed.
Fifth level of knowledge
If the animal does come into the breed's gene pool, his genetic continuity also becomes effective in his progeny, combines with different breeding partners, and with each examined offspring the knowledge climbs in importance beyond his own former breed value. The estimated values themselves swing away (vary) from the average of the true breed value. With each puppy whelped, the points begin again for another first knowledge level, so that the breeder comes full circle and starts all over.
Further knowledge
If a descendant is evaluated, he gives knowledge about father and mother. The father will bring such information to him which is not clearly provided by the mother, and the mother contributes only that which is not explained by the father. The following simple situation should serve as example:
I import a dog and a bitch; nothing is known about their relatives. A litter from these reveals bad HD results. Since the placing of blame on one parent is not possible, both receive uniformly and equally, a bad breed value (e.g., 110).
The bitch whelps a second litter sired by a frequently used stud dog (80 offspring, 30 of them x-rayed, predominantly good hips, & his breed value is 89) and it comes about again that she produces medium and severe HD. Now, the transmission of bad genes by the bitch becomes evident through this second pairing. With a known good-producing dog she has undesirable results! Her breed value index drastically rises thereby. And that has consequences for further use of the imported stud dog that was the sire of the first litter. He is exonerated, and can possibly get 100 or under, although he personally has no further progeny.
The claim
Breed Value Assessment (Zuchtwertschätzung) does not claim to document the truth about the "genes." The preceding conclusions should show this. But it should be a "sign" for the breeding process and give indications of the presence of good or unfavorable genes. The breeder urgently needs these signs. He must supply his kennel with genes from the best families and take into consideration all indications of problems, be they HD, size, character, working ability, etc. If the breed clubs currently offer instruction through this Zuchtwert assessment, at least for some feature urgently in need of attention in the beginning, the breed will develop quickly in the desired direction.
Experiences
Since 1989, Zuchtwertschätzung has been used in other clubs, with subsequent breeding programs, but also for non-binding information.