RVC research into conformation and IVDD published July 2013

Post date: Jul 25, 2013 8:13:9 AM

The Dachshund Breed Council’s Health Committee is really pleased to see Rowena Packer’s research published, as back disease is our number one health priority to address, given its high prevalence. We have spoken with her several times about her work and were delighted to welcome her to our Breed Conference in 2012. Her paper provides some fascinating insights into the complexity of back disease in a range of pedigree breeds, not just Dachshunds, and cross-breeds.

Our own Health Survey of 1500 dogs, which is referred to in the paper, confirmed to us in 2012 the prevalence of back disease and showed the extent to which it is age-related, as well as highlighting some significant variations between the six varieties of Dachshund. Our survey also showed that pet-owned Dachshunds were twice as likely to be reported with back disease as show-owned ones.

The paper's Abstract is as follows:

Intervertebral disc extrusion (IVDE) is a common neurological disorder in certain dog breeds, resulting in spinal cord compression and injury that can cause pain and neurological deficits. Most disc extrusions are reported in chondrodystrophic breeds (e.g. Dachshunds, Basset Hounds, Pekingese), where selection for ‘long and low’ morphologies is linked with intervertebral discs abnormalities that predispose dogs to IVDE. The aim of this study was to quantify the relationship between relative thoracolumbar vertebral column length and IVDE risk in diverse breeds. A 14 month cross-sectional study of dogs entering a UK small animal referral hospital for diverse disorders including IVDE was carried out.

Dogs were measured on breed-defining morphometrics, including back length (BL) and height at the withers (HW). Of 700 dogs recruited from this referral population, measured and clinically examined, 79 were diagnosed with thoracolumbar IVDE following diagnostic imaging 6 surgery. The BL:HW ratio was positively associated with IVDE risk, indicating that relatively longer dogs were at increased risk, e.g. the probability of IVDE was 0.30 for Miniature Dachshunds when BL:HW ratio equalled 1.1, compared to 0.68 when BL:HW ratio equalled 1.5. Additionally, both being overweight and skeletally smaller significantly increased IVDE risk. Therefore, selection for longer backs and miniaturisation should be discouraged in high-risk breeds to reduce IVDE risk. In higher risk individuals, maintaining a lean body shape is particularly important to reduce the risk of IVDE. Results are reported as probabilities to aid decision-making regarding breed standards and screening programmes reflecting the degree of risk acceptable to stakeholders.

The Dachshund Breed Standard

The General Appearance clause says... Moderately long and low with no exaggeration, compact, well muscled body, with enough ground clearance to allow free movement. Height at the withers should be half the length of the body, measured from breastbone to the rear of thigh (see image, below).

The RVC paper primarily used Back Length (BL) as a key measurement, whereas our Breed Standard quotes Body Length. Some very “quick and dirty” measurements from a small number of photographs suggest our 2:1 ratio approximates to an RVC BLHW equivalent of 1.3-1.4. Measurements of some photos of FCI Dachshunds approximate to RVC BLHW values of 1.2-1.4. Photos of Dachshunds with clearly exaggerated length and lack of ground clearance show RVC BLHW values of 1.5-1.7. The Breed Mean for BLHW of Miniature Dachshunds in the RVC paper was 1.5.

Key Points from the paper

This latest paper provides us with evidence we can use to further our programme of health improvement in the breed. There are some key points which we will have to make use of in working with different stakeholder groups to reduce the prevalence of back disease:

- Breeders should be selecting away from exaggerations in length of back and shortness of leg. With fewer than one in six Miniature Dachshund breeders being involved in the show and breed club community, it will be a real challenge for us to reach all breeders and we will need help from the Kennel Club and vets to do this.
- The Breed Council's Health Committee will need to review the Breed Standard and identify how to ‘map’ the BLHW ratio described in the paper, to our current guidance on length to height (which is measured from different reference points on the dog's body).
- Exhibitors and judges need to reflect on the evidence that longer dogs are more prone to back disease and remind themselves that our Breed Standard calls for a moderately long dog, with good ground clearance. Adopting the KC's Breed Watch system could provide a mechanism for judges to report concerns and allow us to monitor what is happening in the show ring.
- It was shocking to see that nearly half the Miniature Dachshunds in the study were overweight and around one in eight was substantially overweight. All owners and vets need to be more proactive in addressing issues of diet and exercise, and recognising the impact of these lifestyle factors on back disease.
- The fact that miniaturisation leads to an increased risk of back disease is a key message to get over to the general public who seem to be increasingly keen on ‘teacup’ and ‘handbag’ dogs. Although this is not an issue in the show ring, it is something we are aware of from Internet puppy adverts and will have to factor into our buyer education.

As with much research, the paper raises as many questions as it answers. For example, why are there differences between the different varieties of Dachshund; why were cross-breeds the second most highly presented dog with back problems and why does a short-backed breed like Cockers also appear to have a problem with backs? We also need to understand why Dachshunds bred under the FCI Standard suffer similar levels of back disease to UK dogs, despite them having longer legs and shorter backs.

To a large extent, the paper confirms what we already know:

The biochemistry of the discs in chondystrophic breeds is altered by the mutation that causes the short legs, and this predisposes to IVDD, so logically a high proportion of dogs with IVDD will be chondrodystrophic breeds.
- Some backs are longer than others. The finding that the longer back length the higher the risk, reinforces the importance of the 2009 change to the breed standard to emphasise the need to avoid exaggeration in length or lack of ground clearance.
A number of other papers over the years have shown that there is an increased risk of back problems with increasing levels of obesity - veterinary advice is to keep your dachshund slim.
Interestingly, the DachsLife 2012 survey indicated that Standard Smooths had the highest risk of IVDD, rather than the Miniatures highlighted by this research. This needs looking at in more detail.

Members of our Health Committee will be meeting with representatives of the RVC team who carried out this research to discuss the results, identify practical actions we can implement and consider the scope for future work.

We shall also be continuing our IVDD DNA research project which is underway with the Animal Health Trust and continuing to investigate the use of Thermal Imaging as a way of identifying healthy backs.