Page 14 - K9News_Issue12_July2020

Results The hip scheme is thus a tool, and indeed the
best tool there is for generating information
In my earlier article I only looked at the
for breeders to use, and breeders have well
relationship of TT Breed Mean Hip Score to
and truly made use of this information, as is
the Year of Publication of the Hip Score from
demonstrated in the paper by the improvements
1984/88 to 2018, so I will just concentrate on
that have been achieved.
the effect of year on the Breed Mean Score
(BMS) as reported in the scientific paper My
An important feature of joint disease, as pointed
results yielded a regression coefficient of 0.15
out in the paper, is that HD is categorized as a
(see Figure 1 above), which means that TT Hip
developmental disorder, but unfortunately it is
Scores improved by 0.15 of a score per year
not always recognised as such in some circles.
over the 34 years of the hip scoring scheme (i.e.
While there is an underlying complex genetic
a 34-year total improvement of 5.1 in TT Breed
component (polygenic – under the influence of
Mean Score).
several genes), there is also an environmental
influence on dysplastic disease, and the
The new scientific paper gave regression
consequential degenerative joint disease (DJD)
coefficients of 0.15, 0.23, 0.27, 0.28, 0.32 and
does not usually become clinically apparent until
0.64 for the three-year Rolling Breed Mean
after breeding age, and this is why dogs must
Scores regressed on Year of Birth from 1990
be at least 12 months old for screening in the
to 2014 for the six breeds. This equates to
British Veterinary (BVA)/Kennel Club (KC) HD
total improvements in breed mean hip score of
Scheme (usually two years old at screening in
between 4 and 16 for the six breeds over the
the USA).
25 years in the scientific study. It was pointed
out that the most rapid improvement was for the
The next step forward, already in place for
breed that started with the worst hips.
breeds that have had large numbers of dogs
scored, is the computation from the hip scores
The results of the scientific paper thus supported
of Estimated Breeding Values (EBVs), which
my own conclusions in the earlier article, both
discount the environmental component thereby
analyses showing a general decline in the
giving an estimate of the genetic status of a
Breed Mean Scores (average scores) over
dog for producing good/bad hips. The use of
time, also accompanied by a reduction in the
EBVs by breeders will lead to greater and more
number of very high scores, thereby revealing
rapid progress in reducing the prevalence of hip
a reduction in the prevalence and severity
disease (see Figure 2 above).
of HD. Furthermore, in the scientific paper,
the proportions of sires and dams with no hip
My example of TTs showed an improvement in
scores fell substantially over time, indicating an
BMS of 5 points in 30 years when selection of
increase in the rate of participation by breeders
parents was based on phenotype (i.e. based on
in the HD Scheme; and of those sires and dams
hip score alone). Lewis et al (2013) in another
that were scored there was a demonstrable
peer reviewed scientific paper (in BMC Genetics
improvement in their scores, indicating that
2013, 14:16) calculated that to achieve an
better hipped dogs were selected for breeding.
improvement of 5 points in the median hip score
via phenotypic selection would take from 30
Recognition to 300 years depending on the breed, but the
same improvement via genetic selection using
It is important to recognise that a hip screening
dogs with EBVs below the breed average could
scheme per se does not improve hip health, it
be achieved in between 9 years and 18 years.
is breeders that improve hip health by using the
information generated by the scheme to select
appropriate combinations of sires and dams.

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K9 NEWS DIGITAL / JULY 2020