What is Intervertebral Disc Disease?
There are different types, but dachshunds are particularly affected by a highly heritable one called Hansen type I. The disease is very prevalent in dachshunds with a rate of about 20% give or take 5%. In the UK, the Dachshund Breed Council reports that about 1 in 4 sausagedogs are affected by IVDD. This type of disc disease often leads to an acute herniation where the disc ruptures and the material inside is forced out, frequently into the spine, where it can damage nerves. There are different degrees of symptoms, stage 1 to 5, where 5 is the most severe. Symptoms include pain, difficulty walking, paralysis and incontinence.
In some cases, the damage to the spinal cord is so great that progressive myelomalacia occurs, where the paralysis spreads throughout the body, including to the heart and lungs. There’s no cure for progressive myelomalacia at the moment and it is fatal.
Why do dachshunds get IVDD?
Dachshunds are a chondrodystrophic breed, a dwarf breed, and have short legs not a long back, in contrast to popular belief. The short legs are due to a gene mutation that happened long ago, maybe as far back as 4000 years ago. These genes also harbour a predisposition for early degeneration of the discs, the shock absorbers between the vertebrae in the back.
The spine ages in all dogs, but in the dachshund this ageing process starts very early. Changes in the discs can be seen already at birth, according to the Norwegian Kennel Club in their breeding strategy for dachshunds. A biochemical reaction leads to changes in the discs, that’s to say degeneration of the core, and in time calcifications that are visible on x-rays.
When a disc ruptures, the outer ring in the disc opens and the material inside it is forced out and often into the spine and can cause damage that can lead to, amongst other things, pain, paralysis, and incontinence.
Disc herniation is a bit like when a doughnut is squashed and the jam spurts out. Imagine a doughnut between each of the vertebrae in the spine.
A rupturing disc is a bit like a squashed doughnut.
How can you reduce IVDD?
By x-raying the dog’s back, you can see calcifications in the spine. The more calcifications there are, the higher the risk of herniation. Research shows that hounds with 5 or more calcifications have 14 times higher risk of rupturing a disc than those with under 5.
Back x-rays have to be done when the dog is between 2–4 years old, because this is when the calcifications are most visible on x-rays.
The degree of degeneration varies from hound to hound, but by counting the number of calcified discs we can see how extensive the disease is in each dog. This number is called the IDC number and it is used to give dogs a Grade from 0–3.
Is IVDD hereditary?
Yes, the IDC number, or Grade of calcification in the discs has a high degree of heritability. Actually, higher than for hip and elbow dysplasia, which have mandatory x-ray screening through the Kennel Club in several countries for many breeds. Hounds with many calcifications are more likely to have puppies with a lot of calcifications. X-ray screening can set a back score for a hound.
Sometimes a dachshund might have a herniation without calcifications having been seen on x-ray, but when a CT scan or histological examination has taken place, calcifications have always been found in the tested material. The connection between calcifications and disc rupture is a clear indicator, it’s just that occasionally the calcification doesn’t show up on x-rays.
What is a back score or Grade?
A back score is given on the basis of the IDC number, the number of calcifications. Grade 0=Clear (0 calcifications), Grade 1=Mild (1–2), Grade 2=Moderate (3–4), Grade 3=Strong (5 or more).
Clear indicates the lowest risk of herniation and for passing it on to the next generation of puppies, while Strong indicates the highest risk.
This is about risk and isn’t a 1:1 relation. For example, not everyone who sets out to sea during a hurricane will end up shipwrecked, but there’s a big risk.
In order to better calculate the risk a hound has of passing on IVDD, we can use a method called Estimated Breeding Value, which is a kind of index.
At the moment, only Denmark has an EBV for dachshunds. IVDD back screening is mandatory there through the Danish Kennel Club and they have already started to see a positive trend. For example, the calcification average in their dachshunds has decreased, according to a study by Andersen and Marx.
In the UK, there’s an EBV for elbow and hip dysplasia, but not for IVDD, even though IVDD has a higher degree of heritability than elbow and hip dysplasia.
Risk isn’t a 1:1 relationship. A bit like setting out to sea in a hurricane. It might be fine, but it’s risky.
What is Estimated Breeding Value?
EBV is a complicated formula used for breeding characteristics that are produced by several different genes.
The average, which is what each hound has as a comparison, is set at a value of 100 and each individual gets a number above or below 100. This shows how the hound compares to the average of the breed. Numbers below 100 are lower than average, while numbers above are better. So, EBV shows the estimated breeding value of the dog and doesn’t just give us information about the status of that particular hound, but also what we can expect from its puppies.
As part of this calculation, the dog also gets a safety number, which indicates how well the index represents the actual breeding value. In other words, it represents a correlation between the estimated and the actual breeding value. The number has a value between 0 and 1, where 0 is no correlation and 1 is complete correlation.
Why don’t we have an Estimated Breeding Value in the UK?
Good question! We need to use the IVDD Screening Program, so it can be set up. We already have EBVs for hip and elbow dysplasia in place through the Kennel Club.
How come there isn’t a genetic test for IVDD if it’s genetic?
Because the heritability is polygenic. Several genes are responsible for the development of IVDD, so developing a genetic test isn’t that easy. But there’s still a chance a “main gene” can be found. Researchers are hopeful that one day this might be discovered and could help healthy breeding. But until that happens, our best tool is x-ray screening.
What about environmental factors?
A lot depends on genes, but environmental factors are also important. Some are known, such as exercise being beneficial, but others are still unknown. Hunting dogs have 50% less risk of developing IVDD, compared to dachshunds that are not working dogs.
You can help your hound by keeping them fit for fight and not neutering them. For example, stairs in moderation are fine, but use common sense and don’t let your dog climb 5 floors daily to stay in shape. And remember that it’s almost never your fault if your sausagedog ruptures a disc. Dachshunds primarily develop IVDD, because tragically they are genetically predisposed to it.
Why is it just recommended and not obligatory to screen for IVDD through the Kennel Club?
Great question! A huge step in the right direction has just been made by the Kennel Club taking over the Dachshund Breed Council’s IVDD Screening Programme and making IVDD screening a recommendation for the Assured Breeders Scheme. But there’s still a way to go.
In Denmark, the Danish Kennel Club has made IVDD screening mandatory for all dachshunds used for breeding. This is because of the well established need for preventative action and the well documented use of x-ray screening as an effective tool.
What will happen if we don’t do anything?
If we don’t do anything, young animals will continue to become paralysed, suffer and die prematurely. Research clearly shows that the prevalence of IVDD is high: about 20% give or take 5% or around 1 in 4. And the short legged breeds have the highest rates of herniation. It can be hard to take in the fact that the levels are so high, but one look at social media and the spaces dedicated to IVDD is enough to tell you that we’re not alone in our experience of IVDD-stricken four-legged family members. Dachshund organisations around the world unanimously recognise IVDD as the breed’s most serious health problem.