Monday, 5 October 2015

Hoof Wall Separation Disease Updated Statistics October 2015

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.


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.


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 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 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 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.

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.


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 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.

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.