Tail Length

Tail Length

Tail length varies greatly between dog breeds and individual dogs. Some breeds have long tails, such as the Golden Retriever, German Shepherd, Border Collie, and Siberian Husky. Other breeds typically have shorter tails, such as the Pembroke Welsh Corgi, Boston Terrier, and Schipperke. The tail contributes to a dog’s physical appearance, but it also plays an important role in balance, communication, and steering while swimming.

Apart from tail docking (the partial removal of the tail), which is banned in many countries unless medically necessary, tail length can also be influenced by genetic factors. Two genetic traits that can result in a shortened tail are natural bobtail and screwtail.

Natural bobtail

The natural bobtail phenotype is caused by a mutation in the Brachyury gene, also known as T gene, which encodes a T-box transcription factor (TBXT). This gene plays an important role in early embryonic development, especially in the formation of the spine and tail. The mutation was first discovered in the Pembroke Welsh Corgi, but has since been reported in several other breeds.

The bobtail trait is autosomal dominant, meaning that dogs with one copy of the mutation (heterozygous state) are expected to have a naturally shortened tail. In heterozygous dogs, this mutation does not cause spinal deformities and is generally considered safe when managed responsibly breeding programs. However, when a dog inherits two copies of the mutation (homozygous state), the condition is usually early embryonic lethal. This means affected embryos do not survive to birth, and therefore this genotype is not expected to be seen in living dogs. As a result, breeding two natural bobtail dogs together can lead to reduced litter sizes. Very rarely, if homozygous individuals were to survive, they would be expected to show severe developmental abnormalities.

Importantly, not all short-tailed dogs carry the T gene mutation. Other genetic factors can influence tail length in breeds such as Spaniels, Schnauzers, and Rottweilers.

Screwtail

Screwtail, also referred to as Robinow-like syndrome, is another genetic condition affecting tail structure. Screwtail is caused by a mutation in the Dishevelled 2 (DVL2) gene. DVL2 is involved in the Wnt signalling pathway that controls embryonic skeletal development. The mutation in the DVL2 gene results in a non-functional or altered protein, disrupting normal development of the spine and vertebrae. The screwtail trait is autosomal recessive with incomplete penetrance, meaning that dogs must inherit two copies of the mutation to be affected and not all dogs with two mutated copies will show the same degree of visible signs.

This mutation is identified in breeds such as the Boston Terriers, Bulldogs, and French Bulldogs, where it contributes to the characteristic shortened, kinked “screw” tail and the typical bulldog-type body shape.

Unlike natural bobtail, screwtail can be associated with health concerns. Affected dogs are typically born with a shortened, twisted tail caused by fused or malformed vertebrae. In some dogs, additional vertebral abnormalities may occur. These can lead to spinal deformities, back pain and neurological problems such as weakness or incoordination. The degree of tail twisting can also lead to dermatitis around the (base of the) tail.

The DVL2 mutation is also associated with characteristic breed features such as a broad head, widely spaced eyes, short muzzle, and small stature or compact body size. The degree of these changes varies between individuals but is often noticeable at a young age. In some dogs, the associated body structure may contribute to breathing difficulties (brachycephalic obstructive airway syndrome, BOAS) and increased stress on the spine and joints.

Relevant tests

• H487 (Natural Bobtail)
• H146 (Screwtail)