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. 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.
Thanks to John Paver for the use of this article.