What Danish data tell us about IVDD X-ray screening and Dachshund breeding

Can spinal X-rays help breeders reduce the risk of intervertebral disc disease (IVDD)? A newly published study of Danish Dachshunds adds useful evidence to the discussion. It also explains why selecting for healthier backs must be balanced with maintaining genetic diversity. In my opinion, this could be one of the most important recent IVDD research papers to support the X-ray screening programme. Stacey Sullivan, Michelle Kutzler (co-authors) and all the Danish owners whose dogs have been screened should be warmly applauded.

IVDD affects the discs that cushion the bones of the spine. When a disc has degenerated and extrudes (IVDE), it can cause a range of symptoms from pain through to paralysis. The condition is common in Dachshunds, but its development is multi-factorial, including genetics, environment and lifestyle factors.

What does a K-number mean?

A spinal X-ray can reveal calcified discs: discs containing mineral deposits that show up on the image. The number seen is called the K-number. A dog with K0 has no visible calcified discs; a dog with four is K4.

Previous research has linked higher K-numbers with a greater risk of clinical IVDD. That makes the score useful for assessing risk, but is not a diagnosis or a guarantee. A K0 dog can still develop IVDD, and a dog with a higher score will not necessarily become affected.

The question for breeders is whether choosing parents with lower scores also makes a difference to their offspring’s scores.

What the researchers studied

Stacey Sullivan and Michelle Kutzler analysed records for 2,120 Danish Dachshunds screened between 1990 and 2024. For 690 of these dogs, the researchers had scores for both parents as well as the offspring. They examined how the parents’ scores related to those of their offspring and modelled the effects of different breeding restrictions.

This was a retrospective study: the researchers examined existing records. They also considered the potential consequences of stricter selection for the size of the breeding population.

Both parents’ scores matter

The main finding was consistent: higher scores in either parent were associated with higher scores in offspring. The researchers found no clear evidence that the mother’s score mattered more than the father’s, or vice versa. Taking both scores into account was more informative than looking at either alone.

Offspring of two K0 parents generally had favourable scores. Of the 66 scored offspring from these pairings, 56 (85%) had a score of K0, K1 or K2. However, five (7.6%) scored K5 or higher.

That distinction matters. Selecting low-scoring parents improves the odds for a group of offspring but it does not predict the result for every puppy. The study supports the use of X-ray scores in breeding decisions, but it does not ensure IVDD is entirely avoidable.

Was IVDD actually reduced?

The study did not directly measure clinical IVDD in the offspring. Instead, the researchers used previously published estimates of IVDD risk for each K-score category to calculate what disease prevalence might be expected.

For offspring whose parents both scored K4 or lower, their calculation suggested a 19% relative reduction in estimated IVDD prevalence compared with the overall scored group. This was a theoretical estimate, not an observed reduction in diagnosed cases so the figure should not be treated as proof that screening alone produced that change.

Even so, the observed parent-offspring relationship gives breeders a practical reason to take screening seriously: scores contain information relevant to the next generation.

Why not breed only from K0 dogs?

In the study, tighter score limits were associated with better offspring scores, but they also left fewer dogs eligible for breeding.

A small breeding pool can increase relatedness and reduce genetic diversity, potentially creating other health problems over time. Dachshunds may be numerous overall, but individual size and coat varieties often function as much smaller breeding populations.

For example, the researchers estimated that restricting standard wirehaired breeding candidates to K4 or below gave an effective population size of 179, compared with 52 under a K0-only rule. Effective population size is a measure of the genetic size of a population, not simply a headcount. The Royal Kennel Club uses 50 as the minimum threshold to prevent immediate health collapse in managed breeds. Modern conservation studies suggest raising this minimum to 100 to prevent fitness loss over five generations in the wild. 

These were approximate figures based only on screened, breeding-age dogs. The calculations did not fully account for relatedness or how often individual dogs were used, and screening was voluntary during the period studied. The wider population may therefore differ. Nevertheless, the findings argue against applying a K0-only rule without considering its effect on each variety.

Recommendations for breeders

• Screen prospective breeding dogs through the recognised scheme available in your country, following its guidance on age and assessment.

• Consider both parents’ scores and, where available, information about relatives and estimated breeding values, a statistical assessment of inherited merit.

• Aim for lower scores without making K0 the only criterion. Consider the whole dog, family health, temperament and the genetic diversity of the variety.

• Avoid overusing popular sires. Assess relatedness and choose suitable pairings to avoid the Popular Sire effect.

• Share results honestly, including less favourable scores. Wider participation makes breeding information more useful.
  

Recommendations for puppy buyers

Ask the breeder whether either of parents have been IVDD X-ray screened and what the results were. Discuss what the scores mean, the family’s history of IVDD and the other health considerations behind the mating.

Be cautious of promises that a puppy is “IVDD-free” because its parents scored well. Screening can inform a breeding decision; it cannot guarantee an individual dog’s future health. Once your Dachshund puppy is home, maintain a healthy body condition, follow our advice on appropriate exercise and contact a vet promptly if you notice back pain or changes in movement.

The practical message

This study supports K-number X-ray screening as a useful tool for reducing the burden of disc calcification across generations. It also shows why screening works best as part of a broader breeding strategy, rather than a single pass-or-fail test.

Source: Sullivan S and Kutzler MA, “K-number-based selection in Danish dachshunds: offspring outcomes and implications for genetic diversity,” Journal of Veterinary Internal Medicine, 2026. Read the research paper.