HD Zuchtwert - Breed Value Assessment Number
The best tool for breeders in the fight against canine hip dysplasia (CHD), to come along in years, is the SV's HD Zuchtwert, or Breed value assessment number (HD ZW). The HD ZW number is an estimation of the probability that a dog will produce progeny with CHD.
The HD ZW value factors in many variables in the calculation, but is based mostly on the hip status of a dog's progeny. This is the critical factor in the usefulness of the HD ZW. The dog's own hip status is only one of several important variables in the equation, not the sole determinant. This is because it is possible for a dog with excellent hip status to produce a majority of progeny with CHD. And conversely, a dog with Fair hip status can produce a majority of progeny with excellent hip status. Without factoring in this critical look at the dog's Genotype (what his genes pass on to progeny) in addition to his Phenotype, (what his actual hip status is) real progress can not be made in reducing the incidence of CHD.
So how does it work? Each dog registered with the SV is assigned an HD ZW number at birth, based on its Parents HD ZW numbers. After a dog is x-rayed, its own hip status is factored into his HD ZW. Upon producing progeny of his own, the results of the progeny's x-rays are then factored into the parents HD ZW numbers. The HD ZW number is not a static value. It fluctuates depending on what the dog produces! This is what is important: A dog's Genotype; What the dog produces. Not his Phenotype; what his actual hip status is.
An HD ZW value of 100 has been set as the breed average. HD ZW values LESS than 100 mean the dog produces fewer progeny with CHD than the breed average. A number greater than 100 means a dog produces CHD more often than the breed average. So HD ZW values less than 100 are desirable. HOWEVER, the focus must still be on the Total Dog. Breeding decisions need to include much more than only a dog's HD ZW! Working ability and Temperament are most important!
To allow for this, the SV requires that the calculated HD ZW for progeny of a desired mating be 100 or less. So a bitch with an HD ZW of 80 can be bred to a male with an HD ZW number as high as 120! The pups of a breeding like this would be assigned HD ZW values of 100 at birth. So HD ZW values Less than 100 are not just desirable, they offer greater options in breeding partners. Additionally, stud dog owners can prove their dog's prepotency by accepting breedings to bitches with high HD ZW values.
For breeders in the US, you must register your dog with the SV or USA/SV, and have the dog's x-ray evaluated by the SV for 'a' stamp. This also settles the PennHIP vs. OFA vs. 'a' stamp question. The diagnostic method to determine a dog's hip status is not relevant. The most relevant data comes from a dog's actual production, "Do his progeny have CHD or not."
There are several sources to obtain data on an individual dog's HD ZW value. The SV website has a search engine which allows entering a dog's SV registration number, or parts of the dogs name, to obtain the HD ZW. This site maps that feature in the "HD-ZW Search". You can also buy the data on CD from the SV as a one time purchase, or as a subscription updated quarterly.
This tool is a must have for every serious breeder! And now, every puppy buyer can have additional, useful information, regarding the potential for a puppy to develop CHD.
Change in the reference basis (numerical calculation) of the HD Breed Value Assessment
On 5 February 2000, representatives of the WUSV and the responsible HD evaluation officials met in Viernheim to consult over possibilities for a common Breed Value Assessment. Since various nations' issue official HD classes based (grounded) on differing claims, a standard needed to be devised to guarantee the comparison through controlled interpretation/evaluation/analysis and technical measurements of the x-ray film. For that purpose, the SV measured about 900 films. In conjunction with this international standardization, the SV found it necessary (they changed from using) to no longer set the the BREED Average (Cross-section of the Breed = starting figure of 100) as the reference basis, but instead to select a constant' figure (measure) as the reference point.
On 8 April 2000, the Breed Advisory expressed the recommendation to set the
expected heritability of a dog with the HD hip rating of fast normal' (ALMOST normal, as described by the SV rating standard) as the new reference basis.
This recommendation was accepted at the National convention in Koblenz on 20-21 May. In establishing the standard, the data particulars of a fictional animal with unknown father and unknown mother was used so as to avoid any hip rating influence of related animals. German Shepherd Dogs which produce (pass on) to a standard equivalent to that, receive the numerical hip rating valuation of 100.
The Breeding Plan of the SV is reworded in §2 accordingly.
The committees were of one opinion that, in setting restrictions on the permissible pairings, no adjustments are necessary at the present.....breeders
will be responsible for, and relied upon to, supply the appropriate information to other breeders.
The Breed Value Assessment itself has not changed. The HD (Breed) values are calculated as before, apart from the fact that new data will be updated quarterly. In a second step, the existing heritability numbers will be converted into a relative calculation whereby the BREED average (cross-section of the Breed = 1.70) will no longer be used, but rather the heritability factor of the fictional' GSD with fast normal' hips (2.0) will be set as the reference point (=100).