Hoof Wall Separation Disease
Update
The latest statistics from the HWSD testing performed by VGL Davis
have just been released. These figures cover six months from March
2015 to October 2015. As there are now three time periods covered –
effectively a 12 month period - this information has been combined to
provide an overview both internationally and by individual country.
The information is now sufficient that trends and interpretation can
be drawn from the data.
This raw data from has been converted into graphs and charts to make
the information more easily accessible. A short synopsis follows
each of the graphs.
The first chart shows the total number of ponies tested since
August 2014:
In the initial six weeks after the test became available the lab
tested a large number of ponies in a very short space of time.
After this the demand dropped away. Testing increased rapidly in the
March to October tranche – as this tranche corresponds with the
time after the HWSD meeting held during the Spring Festival, one can
only surmise that the attendees at this meeting went away with a
greater understanding of the need to test breeding ponies for HWSD.
Even
with the increased number of ponies being tested, it is interesting
to note that the percentage of carrier and affected ponies in the
greater population, remains relatively steady. This is the type of
information which becomes both more accessible (and useful) as more
data becomes available.
On
the VGL website page it states “At
the time that this test was released, approximately 15% of Connemara
were carriers of HWSD (N/HWSD) however, the number of carriers can
change with each generation. “
Be
aware that this figure of 15% was extrapolated from the population
used for the HWSD research at Bannasch. The research population
itself was biased, by virtue of the fact that as many affected ponies
and their relatives made up the research cohort. Also important was
the geographical origin/residence of the ponies from which samples
were submitted. The carrier percentage across all countries, which is
now becoming apparent, is in line with what the pedigree research
initially suggested.
Some
countries are showing a very much higher carrier rate than the
average; this could be the result of owners realising which
bloodlines appear to be a concern and then selectively testing ponies
from those bloodlines. However the pedigree research indicated that
with these particular countries, there was always going to be a
higher carrier and affected rate because of the initial animals
imported (and in some cases also subsequent imports) on which the
breed was founded.
This
difference of carrier rates between countries is best illustrated by
the following:
The
differences with the affected rates between countries is not so
obvious because in many cases owners are not choosing to test ponies
with obvious/known hoof pathologies. Some of the affected ponies
which have been tested, and show up in the graph, will be the direct
result of enquiries made to the Connemara Pony Research Group asking
for advice – the given advice being 'test for HWSD and make sure
that is what you are dealing with'.
France
and Ireland fall outside of this above parameter, so sadly some
owners in both of these countries may have been somewhat shocked to
receive the test results on their ponies
Each
country is listed below showing the number of ponies tested and the
distribution and ratios of N/N, N/HWSD and HWSD/HWSD. The carrier
and affected percentages are shown in a second graph.
Australia
Australian
breeders embraced HWSD testing from the very beginning and have one
of the highest uptakes of the test in the world relative to the size
of the overall population. The incidence of HWSD in Australia is
relatively low which is in line with the initial pedigree research.
The
carrier rate remains constant across all of the tranches. This would
indicate that from the number of ponies already tested the likelihood
that 12% or lower will be the carrier rate in the Australian
population at present. This level has the potential to drop without
the loss of genetic diversity through careful breeding choices for
future generations.
Canada
Ponies
from the Canadian population featured highly in the research into the
HWSD mutation and release of the HWSD genetic test. Therefore the
impression given by the initial uptake of the the
HWSD test, relative to the population size in Canada, appearing to be
low results in a false picture of the reality. The steady decline in
numbers tested since the beginning also paints an inaccurate picture
of the true situation. The number of actual breeders in Canada is
very low compared to other countries as is the number of ponies being
produced. The number of ponies actually being bred at present is
also low. The assumption could be made therefore, that the breeders
are selectively testing current breeding stock which was not part of
the research and whose status is not already known.
The percentage of carriers in a such a small population is high.
This is hardly surprising because it was in Canada that the whole
issue of HWSD began to be openly discussed. For those who are
unaware the HWSD issue was first PUBLICLY raised in Canada after the
importation of two stallions and five mares (to expand the limited
gene pool in that country) resulted in 100% HWSD affected foals when
mated to each other. Both stallions and all of the mares were HWSD
carriers; one stallion each from the UK and Ireland and the mares
from Ireland, the UK and the USA.
Denmark
Denmark saw an initial flurry of testing with a subsequent drop-off.
The
carrier rate in Denmark is high, as expected from the initial
pedigree research.
Finland
Finland was slow to commence testing but is showing a steady increase
in the number of ponies being tested. The high relative carrier
rate in the October tranche suggest that several ponies from
'suspect lines' were the first to be tested.
Because of the high initial 'hit rate' of carrier results the graph
for Finland appears quite skewed. Also because there are only two
sets of data listed further testing will result in a more accurate
picture of the HWSD status within the Finnish population. Finland
shares a high level of common blood with the ponies of Scandinavian
countries. It would be expected that the carrier rates in Finland
will reflect those of these other countries.
France
France presents an interesting picture! There was virtually no
interest in HWSD testing or indeed the disease itself, prior to the
March meeting at Clifden. Only one sample was submitted from France
for the HWSD research so the 'situation' in France was unknown to the
researchers; there was concern that France would be sitting on a
'time-bomb' with the influx of cheap imports from Ireland. The one
sample submitted was from such an imported pony and he is an affected
pony. Much of the awareness now about HWSD in France is the result
of hard work by a very small number of individuals working in the
face of much opposition.
The carrier and affected rates in France is skewed once again, this
time by the large increase in the number of ponies in a single
tranche. Testing has revealed that several Irish bred stallions
either resident in France or previously resident there, are HWSD
carriers. Several of the top performing and producing French bred
stallions have also been tested as carriers of the HWSD mutation.
The published results are on the HWSD blog tested ponies results
page.
Germany
A large number (over 270) of the German ponies were involved in the
HWSD research which led to the test becoming available. As a result
the HWSD status of these ponies is already known so the 'low uptake'
of testing in Germany as shown by these figures is inaccurate. It
would appear reasonable to assume that testing is being selectively
applied to current breeding stock not part of the research.
The carrier rate tends to reflect the intermingling of the
different lines from all over Europe and imports from Ireland.
Great Britain
including Northern Ireland
A large proportion of the ponies being tested under the banner of
Great Britain are from Northern Ireland. The VGL recording system
does not differentiate between the post codes. (one can hardly expect
this). This anomaly does result in a misleading graph. Of the
ponies not from Northern Ireland that are being tested a high
proportion are imports from Ireland. Very few of the British results
are from British bred ponies. The high number of affected ponies is
a direct reflection of the ponies which have been imported from
Ireland that then proceed to display HWSD hoof pathology with their
new owners.
Carrier and affected rates are skewed by the true demographics of the
tested population which is not geographically accurate.
Ireland
The total number of tested ponies – although steadily increasing –
is woefully inadequate considering the size of the Connemara pony
population in Ireland. As can be seen, the rate of carrier and
affected test results is also steadily rising. This information
gives, to the discerning breeder, a reinforcement as to why breeding
stock should all be tested.
The carrier and affected rates follow relatively the same gradient.
Initial pedigree research indicated that the expected carrier rate
in the Irish population would be in excess of 40%. There is
insufficient data, because of such low testing numbers, to determine
whether these rates will continue to trend upwards as expected.
New Zealand and
Norway have not been graphed.
The
volume of data on these countries is not sufficient for graphing
purposes. New Zealand has not tested any further ponies since the
previous report in March 2015. A large number of the New Zealand
population contributed samples to the HWSD research, so their status
is already known without undergoing VGL testing. Norway has only
data from the latest tranche.
The
data from Norway is as follows:
| TRANCHE | N/N | N/HWSD | HWSD/HWSD | Grand Total | % of Carriers | % of Affected | Country |
| Mar/Oct15 | 4 | 1 | 5 | 20.0 | 0.0 | Norway |
The Netherlands
The Netherlands has a small population of 'home bred' Connemara
ponies. Also as there is only two of the tranches logged as no
testing occurred during the first the data is incomplete. There is a
slight increase in ponies tested between the separate groupings of
the past 12 months.
The Netherlands shares common bloodlines with the rest of Europe
especially those of Denmark. This reflection is apparent in the
relatively high carrier rate.
Sweden
Sweden shows a consistent number of ponies being tested in the past
12 months. There has been a noticeable increase in the level of
carriers tested. This could be a direct result of the results
published on the HWSD blog page; owners/breeders making the decision
to test solely because of the bloodlines published in the results.
The carrier rate for Sweden was always predicted, by the initial
pedigree research, as going to be high. The high carrier rate
reflects the bloodlines which were initially imported to found the
breed in Sweden. Subsequent imports from various countries have
compounded the issue. As a greater number of ponies are tested, the
expectation is that the carrier rate will rise in this country. Both
the endemic population and recent imports have high carrier
potential. Extreme care is needed to prevent this situation becoming
worse.
United States of
America
The USA is the leading country overall, for the numbers of ponies
that they have had tested for HWSD. Considering that the population
of the breed in the USA is minuscule compared to that of Ireland, the
UK and France, the American breeders deserve a big pat on the back!
Initially there was a goodly number of ponies tested, which then
dropped to half of the initial tranche. There is slight increase in
the latest tranche over the previous period.
The carrier population in the USA is interesting and rather unique.
Research shows that the HWSD mutation came into the USA with the
first wave of imports from Ireland; two in foal mares, which both
went on to produce dynasties of top performers, through multiple
progeny. Subsequent imports in recent times from Ireland, Australia
and the UK have raised the carrier rate as to that which is evident and
depicted in the graph.
Conclusion
The level of reporting of test results lags significantly behind than the testing rates. Where tests are publicly reported it is obvious that owners are acting selectively about which tests they choose to share. There is a higher reportage of N/N results than that of the other two options which results in skewing public perception to accept that HWSD is of a lesser significance than is truly the case.