Chondrodystrophy in Dogs: Short Legs and Fragile Discs

Chondrodystrophy combines two findings: shortened, dysplastic long bones and premature degeneration and calcification of the intervertebral discs (Brown et al. 2017). The cause is retrogenes – extra copies of the growth-factor gene FGF4 inserted into the genome. The retrogene on chromosome 18 (CFA18) is associated with short legs (chondrodysplasia), a trait that defines at least 19 breeds including the Dachshund, Corgi and Basset Hound (Parker et al. 2009). The second retrogene, described in 2017 on chromosome 12 (CFA12), also shortens the legs – and is the key genetic risk factor for disc herniation.

An intervertebral disc consists of a gel-like core, the nucleus pulposus, surrounded by layered fibres, the annulus fibrosus. In chondrodystrophic dogs the core is replaced early by cartilage-like cells, undergoes chondroid degeneration and calcifies – not at one spot but along the whole spine (Brown et al. 2017). In Dachshunds the number of calcified discs visible on X-ray peaks at around 24 to 27 months; heritability is estimated at 0.6 to 0.87 (Bruun et al. 2020).

In a Hansen type I disc herniation, the calcified core can burst explosively through the weakened fibre ring into the spinal canal. The material compresses the spinal cord, causing inflammation and bleeding, severe pain and neurological deficits up to paralysis (Brown et al. 2017). In the DachsLife survey the causative disc was thought to lie in the thoracolumbar spine in 88% of cases (Packer et al. 2016).

The CFA12 retrogene acts dominantly: one copy is enough to raise the risk markedly. The original study reported an odds ratio of 51 for disc disease (Brown et al. 2017), and a follow-up found 18 in mixed-breed dogs (Batcher et al. 2019). Body shape adds to it: in a UK referral-hospital study risk rose with the ratio of back length to height at the withers, and being overweight or skeletally smaller increased it further (Packer et al. 2013).

By moderate proportions, by spinal X-ray results for both parents and by a family without back problems. You cannot see a puppy's discs – but you can see how the parents are built and ask to see their results in the original.

For the Dachshund, the FCI breed standard itself sets the direction: ground clearance should be about a third of the height at the withers, and a body trailing on the ground is a severe fault. Dogs built much lower and longer are not the ideal but an exaggeration of it.

We do not list breeders for the French Bulldog; for that breed, see the page on the short nose.

It shows whether a dog carries the CFA12 retrogene – in no, one or two copies. Because the gene acts dominantly, even single-copy carriers have a raised disc risk. In breeds where not every dog carries it, breeders can use the test to deliberately lower the risk for their puppies.

The gene is not limited to Dachshunds: in a survey of 75 breeds it was found in 53% of them (Batcher et al. 2019). It was discovered in the Nova Scotia Duck Tolling Retriever, a medium-sized gundog, and Beagles and French Bulldogs carry it frequently even though they are not among the extremely short-legged breeds. In mixed-breed dogs it also raised the risk markedly. In other words, you cannot necessarily tell from the outside.

In Dachshunds the test on its own helps little: in Danish smooth- and long-haired Dachshunds the insertion is almost fixed, so nearly every dog carries it. Breeding on the DNA test alone would mean excluding almost the entire breed. The researchers therefore recommend spinal X-ray screening for calcified discs as the more reliable breeding tool. Even in wire-haired Dachshunds, where the gene still varies, the test alone was not a useful risk marker: most dogs with few calcifications carried the insertion too (Bruun et al. 2020).

With a lean body weight, daily exercise and fast action at the first warning signs. Being overweight increased the risk of disc extrusion in a UK referral-hospital study (Packer et al. 2013). In the DachsLife survey of 2,031 Dachshunds, dogs exercised for less than 30 minutes a day were more often diagnosed with disc disease, and dogs exercised for more than an hour less often (Packer et al. 2016).

Stairs and sofas are less clear-cut than many people think: in the same survey, Dachshunds that used stairs daily or were allowed to jump on and off furniture were actually diagnosed less often than dogs that were not. That may partly be because owners forbid it after an episode – the authors stress that these associations do not prove cause and effect. Neutered Dachshunds were also affected more often; whether and when to neuter is best discussed with your vet.

A disc herniation can start gradually or suddenly – in the DachsLife survey, signs developed within less than 24 hours in 42% of dogs. If your dog can no longer move its hind legs, it is an emergency for a clinic with neurology or surgery.

Not across the board – the law does not name specific breeds. Section 11b of the German Animal Welfare Act (TierSchG) prohibits breeding dogs where the offspring can be expected to suffer pain, suffering or harm because body parts or organs are hereditarily missing, unfit for use or altered. Whether a case counts as extreme breeding is assessed individually, based on the animal's traits; under paragraph 2 the competent authority can order animals to be neutered. Owning a short-legged dog is not prohibited – the ban covers breeding.

The provision is interpreted with the help of the “Gutachten zur Auslegung von § 11b des Tierschutzgesetzes (Verbot von Qualzüchtungen)”, usually dated 1999 and written by an expert group appointed by the Federal Ministry of Agriculture. It lists chondrodysplasia with the Dachshund as an example, describes these breeds' tendency to disc herniation and recommends breeding away from very long backs and pronounced short legs to counter exaggerated type. It does not impose a breeding ban for this trait.