A research study funded by Morris Animal Foundation with grants from
The Seeing Eye, Inc. and the Golden
Retriever Club of America has raised quite a few eyebrows. The data,
presented at the 27th Veterinary Orthopedic
Society meeting, held in France in 2000, concerned Golden Retrievers
radiographed for signs of hip joint laxity.
Average age was 11 months. Three views were made, including the traditional
hip-extended one used by OFA and
almost every control registry in the world, and the PennHIP distraction
and compression views that more accurately reveal joint looseness.
In the hip-extended view, the measure of observable laxity was made using the Norberg Angle (NA), and in the view with the femoral heads levered out from the sockets as far as they will go, the measure used is the distraction Index (DI) developed by PennHIP for early and accurate detection of that most important HD risk factor. The study was to determine heritability estimates for the different types of hip scores in this breed. Heritability is a ratio that refers to how much effect "selection pressure" (choices of breeding partners, mostly) has on genetic progress; it is expressed by a number between zero and one (0 - 1). The higher the number, the faster one can make progress (in reducing HD, for example). These heritability numbers vary considerably from one diagnostic technique to another.
The heritability estimate of the subjective hip-extended scoring method
was 0.22 and this was not statistically
different from zero (0). Remember, when we use the word "statistically"
we are talking about a specific mathematical science, not the very loose
use of such words by the general public. The heritability estimate for
the only objective part of the hip-extended view (NA) was 0.46, a big improvement.
Both it and the 0.64 heritability estimate of the DI method are statistically
significant.
Conclusions: Using DI, genetic change (progress in your hip improvement
program) will occur 40% faster than you would expect using the NA, and
a whopping 290% faster than by using the OFA-type hip-extended subjective
method. Further calculations and comparisons showed that the square
roots of these heritability estimates are
important: the subjective hip-extended figure here is 0.47, which means
that if you use just that knowledge to choose breeding partners, you have
no more chance of making a lucky decision (improvement in hips) than if
you had just flipped a coin. The DI square root of 0.8 is twice as high,
and your odds of making a wise move armed with such knowledge are vastly
improved. When you factor in the relatively new and until now obscured
calculation of Breeding Value or Zuchtwert, you can get even more accuracy
and faster progress. The Seeing Eye has been using BV for years, and the
largest breed club in the world, the SV (GSDs) has begun publishing ZW
numbers for all breeding dogs, active or potential. I think when the more
sensible leaders of the Golden club sees these data and conclusions, they
will want to implement a BV-ZW system as well as encourage PennHIP DI use
by breeders.
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Editor’s note: Fred Lanting is one of only two SV conformation judges in North & Central America, and has judged the breed in more than a dozen countries beyond that. His most recent international assignments have included Peru (See USA’s Nov-Dec 1999 issue), India and Pakistan, Edmonton, Jamaica, and Chile. He annually offers a tour of parts of Germany and sometimes neighboring countries for the days before, during, and after the Sieger Show (BSZS), with visits to working-line kennels and clubs as well as show aspects of the breed. He believes in trying to live up to the name of his book, “The TOTAL GSD”.
Fred Lanting, Canine Consulting
3565 Parches Cove Rd, Union Grove AL 35175-8422
Lectures & Seminars on Orthopedic Disorders,
Gait-&-Structure, Etc.