Screw Tail in Dogs: What the Corkscrew Tail Hides in the Spine

The tail vertebrae form incorrectly in the embryo: instead of a chain of uniform, box-shaped vertebral bodies you get hemivertebrae, wedge vertebrae, butterfly vertebrae and block vertebrae that fuse together. On top of that, Mansour et al. (2018) describe bulldog-type tails as lacking roughly 8 to 15 caudal vertebrae. The result is a shortened, kinked or corkscrewed tail.

The most important known genetic factor in English Bulldogs, French Bulldogs and Boston Terriers is a frameshift deletion in DVL2 (Dishevelled 2, c.2044delC), part of the WNT signalling pathway that patterns the developing spine. In that study the variant was fixed in both bulldog breeds and had an allele frequency of 0.94 in Boston Terriers. Every homozygous dog had caudal malformations; thoracic malformations appeared in 45 to 100% depending on breed. Because similar mutations in DVL1 and DVL3 cause Robinow syndrome in people, the canine picture is called Robinow-like syndrome.

When wedge-shaped vertebrae sit in the thoracic spine, the column bends there – upwards (kyphosis), sideways (scoliosis) or downwards (lordosis). In a CT study of 171 neurologically normal bulldogs and Pugs, 80.7% had at least one vertebral malformation, and 93.5% of the French Bulldogs had hemivertebrae. Usually this stays silent. If the vertebral canal narrows, though, the spinal cord is compressed: wobbly gait, hind-limb weakness up to paralysis, and urinary or faecal incontinence can follow. Pugs had hemivertebrae less often, but they were more often clinically relevant.

On the outside, the stub often sits in a deep skin pocket. Moisture and sebum collect there, leading to skin-fold dermatitis (intertrigo) with bacteria and yeast; if the tail becomes ingrown, amputating it (caudectomy) may be necessary. In a case series of 17 dogs, signs resolved afterwards, with short-term complications in roughly one dog in eight. The German veterinary animal-welfare association (TVT) adds the functional loss: a screw-tailed dog can barely cover its anus and genitals, cannot lift the tail properly to defecate and can hardly use it to communicate.

By a tail that works as a tail, and by an unremarkable spine on X-ray or CT. A straight, mobile tail that covers the anus is the visible sign; a report on the thoracic and lumbar spine shows what you cannot see from outside.

In bulldog breeds, length is worth a look: in French Bulldogs, dogs with more tail vertebrae had fewer and milder hemivertebrae, and the number of hemivertebrae is clearly heritable. Even the FCI standard describes the ideal tail as long enough to cover the anus and rather straight. A longer, straighter tail therefore goes with fewer and milder hemivertebrae.

To be honest about the limits: it does not remove the DVL2 variant. Where the variant is fixed in a breed, no dog within that breed is free of it – it can only disappear by crossing in dogs that do not carry it.

We do not list breeders for French Bulldogs or English Bulldogs. If you already share your life with one, these points are your yardstick at the vet.

Because one dog looking healthy tells you nothing about its puppies. Most hemivertebrae in bulldogs are found by chance – in the CT study by Ryan et al., four out of five neurologically normal dogs had at least one vertebral malformation. Silent does not mean harmless for the next generation.

In French Bulldogs the number of hemivertebrae is strongly heritable, with an estimated heritability of 0.58, and it is linked to tail length: fewer tail vertebrae, more hemivertebrae. The authors warn that prevalence could rise if dogs with shorter tails are preferred for breeding. Selecting for a short tail means selecting for the back as well.

On top of that, some dogs do develop neurological deficits, and then treatment is demanding. That is why the German expert opinion on extreme breeding relies on X-raying breeding dogs – before the puppies exist, not at the vet afterwards.

The natural bobtail of breeds such as the Pembroke Welsh Corgi or the Australian Shepherd comes from a different mutation: a variant in the T-box gene (T, c.189C>G). It is inherited dominantly – one copy is enough for a short tail. Two copies appear not to be survivable: a study across 23 breeds found not a single homozygous dog, and crossing data point to early death in the womb.

For breeding this means that when two bobtails are mated, about a quarter of the embryos are expected to be lost. In Swedish Vallhunds, such litters were on average 29% smaller than litters from long-tailed parents. The rule is therefore to pair a bobtail with a long-tailed dog, never two bobtails.

There is no ban that names the screw tail specifically – Section 11b of the German Animal Welfare Act (TierSchG) does not list individual traits. It prohibits breeding vertebrates where offspring can be expected to suffer hereditary pain, suffering or damage because body parts or organs are missing, unfit for their species-appropriate use, or altered.

The interpretation aid is the German agriculture ministry's expert opinion on Section 11b (“Gutachten zur Auslegung von § 11b des Tierschutzgesetzes”), usually dated 1999. It is not law, but it explicitly covers shortened or absent tails and crippled tail vertebrae (corkscrew and kinked tails), recommends X-ray screening, advises a breeding ban for animals that have vertebral defects elsewhere in the spine besides the tail malformation – and calls for breed standards to drop the corkscrew tail. The German veterinary animal-welfare association (TVT) treats even a too-short or missing tail as damage within the meaning of Section 11b.

Since 2022, dogs with inherited extreme-breeding traits may also no longer be shown in Germany at exhibitions or other events where dogs are judged (Section 10 of the Dog Welfare Ordinance). Owning a dog with a screw tail, on the other hand, is not prohibited – the ban covers breeding and exhibiting.