CDDY/IVDD: A Practical Guide for Breeders and Owners
This article on CDDY/IVDD is not intended to be a scientific paper. On the contrary, it is an attempt to provide a practical classification for breeding purposes regarding this genetic disposition and to make the topic accessible to dog owners. Throughout the text, you will find several links regarding risk factors, development, and more.
Defining the Basics: What do CDDY and IVDD actually mean?
CDDY describes a (retro)gene located on chromosome 12, which is responsible for a form of short-leggedness (chondrodystrophy) in certain breeds. There are many breeds where dogs are either carriers or have inherited the gene from both parents. These include Dachshunds, French Bulldogs, and specifically Cocker Spaniels (both Show and Working types). In these three breeds, the number of dogs carrying the gene from both parents is extremely high, and the total percentage—including „simple“ carriers—is nearly 100%.
This gene can be identified through genetic testing, which determines whether a dog carries a single copy or two. An explanation regarding testing methods can be found at the end of this text. I would like to further explain the implications of the fact that practically all Cockers carry this gene (either heterozygously, meaning one copy, or homozygously, meaning two copies).
CDDY is not only a gene that causes short-leggedness (there are other genes that do this as well, though they are not relevant here); it can also lead to premature calcification of the intervertebral discs. Ideally, discs should be one thing above all: flexible structures filled with a jelly-like substance that act as buffers to maintain spinal stability while allowing for flexibility. If this structure hardens at a young age, the risk of a herniated disc increases.
This leads us to the second term:IVDD (Intervertebral Disc Disease) refers to anything from a bulging disc to a complete prolapse or a rupture of the disc structure. IVDD is not a genetic test but a clinical diagnostic term used by veterinarians—essentially a collective term for disc problems. IVDD occurs in various grades, which are described in one of the linked videos.
In summary, the gene in question is one risk factor among several that can lead to IVDD. Research suggests it follows a dominant inheritance pattern (meaning even a single copy of the gene can lead to premature calcification). Consequently, the risk of developing IVDD is significantly increased.
The Prevalence Puzzle
The question remains: Why do so many French Bulldogs and Dachshunds suffer from this condition—at a disproportionately higher rate within their populations—compared to Working Cocker Spaniels (WCS)? In England, the Cocker Spaniel is the second most bred breed. Given the carrier percentages, one would expect many more clinical cases.
Here’s the thing:While the CDDY gene should absolutely not be underestimated, other influential factors and risk factors clearly play a decisive role. Breeds with a disproportionately long back (such as Dachshunds, but also many German Shepherds) face much higher mechanical stress on their discs due to their skeletal structure. IVDD is the most common orthopedic back disease in dogs. Estimates show that 2–3% of all dogs across all breeds—regardless of carrier status—will develop it during their lifetime. Cornell University notes that approximately 10% of dogs carrying two copies of the gene become ill. While this sounds like an extremely high risk, the same university states that in the USA, Dachshunds account for 40%–75% of all cases (Source: Cornell / ACVS
This group is largely responsible for the high percentage of illnesses among gene carriers.
In the USA, Dachshunds are indeed much more common than Cocker Spaniels. However, even in England, where Cocker Spaniels (the vast majority being Working types) are bred extensively, the Dachshund remains the breed most frequently affected by IVDD, followed by the French Bulldog.
A study published in the Journal of Veterinary Internal Medicine concluded that IVDD development is likely influenced by multiple genes. Furthermore, external factors play a role (interestingly, high levels of exercise do not increase the risk for Cockers). It is important to note that dogs from show lines have a significantly higher risk of falling ill.
Here the link to the study:
https://academic.oup.com/jvim/article/40/1/aalaf011/842971
The Status Quo for Working Cockers
IVDD is indeed an issue within the breed: the prevalence in Working Cockers is approximately 3.44%, which is higher than the general dog population (approx. 2–3%). However, compared to other breeds that are also nearly 100% CDDY carriers, this is remarkably low. This suggests that other risk factors contribute significantly to the development of IVDD—such as the aforementioned spinal mechanics of the Dachshund or the vertebral malformations seen in Bulldogs.
Summary:WCS have, on average, a 1.7 times higher risk of developing IVDD compared to the general dog population. While the exact extent to which calcification contributes to clinical cases is not fully known, it certainly predisposes dogs to herniated discs. The existing genetic test identifies a risk factor; dogs with one or two copies of the gene do indeed frequently show premature disc calcification.
For a deeper dive, this video explains IVDD and the increased risk through calcification:
https://www.youtube.com/watch?v=jaDjY6M1QfM
Conclusion:The CDDY genetic test is included in standard packages from companies like Embark and Wisdom Panel/MyDogDNA. It would be unwise to ignore it entirely. However, it only describes one risk factor. Without outcrossing, breeding toward „clear“ dogs is utopian due to the existing gene pool. Nevertheless, monitoring this risk factor is advisable, especially in combination with spinal X-rays, which are recommended for breeding hygiene. These images are most conclusive in dogs over two years of age.
A Note on Testing Methods:It is vital to know that Embark uses a „marker test.“ This test does not detect the (retro)gene itself but rather markers that indicate its likely presence. This frequently leads to inaccurate results for dogs that are actually „clear“ or carry only one copy. I personally re-tested approximately 10 dogs with Wisdom Panel/MyDogDNA that were previously labeled „clear“ or „carrier“ by Embark; every single one of those initial results was incorrect. If you require a reliable CDDY result, Embark may not be the preferred choice.