Australian Shepherd Natural Bobtail (TBXT): A 2009 23-Breed Study

SamOur Aussie puppy was born with a stubby tail and the breeder says that’s natural. How would I even know?

Elena MarshUsually you can’t tell by looking, and that is exactly the gap a DNA result fills. A 2009 Journal of Heredity survey traced natural bobtails in 17 breeds back to one shared change in the same gene.

SamPeople online say breeding two bobtailed dogs is dangerous. Is that a myth or a real problem?

Elena MarshIt is real, but it is not the spinal story most forum posts tell. The 2001 work at University College London concluded from bobtail-to-bobtail crosses that embryos with two copies of the variant do not survive.

SamAnd if I just want a healthy pet, does any of this matter for my dog?

Elena MarshFor an adult pet it matters much less than for a litter. A Norwegian veterinary school X-rayed 19 adult bobtailed Corgis and found no congenital spinal defects, so the weight of this topic falls on breeding and on newborns.

Bottom line: A natural bobtail (NBT) in the Australian Shepherd comes from one copy of a single change in the TBXT gene, c.189C>G (p.Ile63Met), the same ancestral variant that Hytönen and colleagues found in 17 short-tailed breeds in a 2009 survey of 360 dogs from 23 breeds. One copy gives a short tail; two copies usually end development before birth, which is why pairing two bobtails tends to shrink litters (a 29% drop was measured in Swedish Vallhunds, not in Aussies). The test is sold under older names (T, T-box, brachyury) and in three different allele notations. A result is risk and breeding information, not a diagnosis; a puppy born without a tail, with a weak rear end or unable to pass stool needs a veterinarian the same day.

Aussies are the 14th most registered breed in the United States in the American Kennel Club’s 2025 statistics, and their tails are one of the few breed features where the written standard explicitly accepts two different origins. A short tail on an Aussie may be docked in the first days of life or present at birth, and the AKC and ASCA standards treat both as correct. That makes the bobtail gene less of a health screen and more of a record-keeping and mate-selection tool.

360 dogs and 23 breeds: what the 2009 survey says about the Aussie tail

The single most useful paper for an Aussie owner is not about Aussies alone. In the 2009 Journal of Heredity study by Hytönen and colleagues, a collaboration that included the CNRS and University of Rennes genetics group, the authors sequenced the T-box gene in 360 dogs from 23 breeds other than the Pembroke Welsh Corgi. Of those dogs, 156 had naturally short tails.

The answer was “in many breeds, but not all”. In 17 breeds the variant was present and, in the authors’ words as quoted by OMIA, showed “a perfect correlation” with the short-tail phenotype: every natural bobtail had it, and dogs with full tails did not. The Australian Shepherd is on that list of 17, together with breeds such as the Swedish Vallhund, Brittany, Jack Russell Terrier, Polish Lowland Sheepdog, Spanish Water Dog, Pyrenean Shepherd, Mudi, Croatian Sheepdog and Schipperke. The list is reproduced by the Czech laboratory Genomia, and all 17 breeds also appear in OMIA’s (longer, 20-breed) list. The survey was led from the University of Helsinki.

Two limits are worth stating plainly. First, we could not obtain the paper’s per-breed table, so how many Aussies were genotyped is not known to us and we do not quote a figure. Second, no published allele frequency for the variant in US Australian Shepherds turned up in our search. Statements such as “one in X Aussies carries it” have no published source behind them as of October 2026.

The third finding is the one breeders tend to remember. Among all 360 dogs, not a single one carried two copies. As the abstract puts it, “No dogs were found to be homozygous for the C189G mutation, suggesting that the homozygous condition is lethal.”

Six bobbed breeds that lack the variant, and why that protects Aussie buyers

The same survey found six short-tailed breeds in which neither c.189C>G nor any other change in the coding part of the T-box gene was present. Genomia lists them as the Boston Terrier, English Bulldog, King Charles Spaniel, Miniature Schnauzer, Parson Russell Terrier and Rottweiler, and tells customers it does not recommend the bobtail test for those breeds. Their short or kinked tails come from other mechanisms. Animal Genetics, for example, sells a separate Screwtail test for a different tail shape.

For Aussie owners this has two practical consequences. The first is reassuring: because the Aussie belongs to the group where the variant tracked tail type perfectly, a TBXT result in this breed is meaningful. A natural bobtail Aussie is expected to carry one copy, and a full-tailed Aussie is expected to carry none. The second is a caution about mixes. If a dog is part Aussie and part one of the six breeds above, a negative result does not prove the short tail was docked; it may simply be a short tail of the other kind. The same applies to cats, whose short tails in Asian breeds were linked to a different gene, HES7, in a 2016 Scientific Reports study, so cat data should never be read across.

One amino acid in a developmental switch: how c.189C>G shortens the tail

The gene behind the trait was identified in 2001 by a team at the MRC Human Biochemical Genetics Unit at University College London. Their paper in Mammalian Genome (Haworth et al. 2001) mapped the trait to dog chromosome 1 and found a single-letter change in a highly conserved region of the T-box transcription factor, the protein historically called brachyury. That protein switches on other genes during the development of the back end of the embryo. The variant swaps isoleucine for methionine at position 63, inside the DNA-binding domain, and the UCL group showed the altered protein binds its DNA target poorly.

The official gene symbol today is TBXT, according to NCBI Gene record 403653, but the older symbol T is still everywhere. On an order form the test may be named “T Locus”, “T-box”, “Brachyury”, “Short Tail” or “Natural Bobtail”. They all refer to the same variant.

Inheritance has two faces. For the tail, the variant is dominant: one copy is enough for a bobtail, and the length varies from almost no tail to a stump of a few centimetres up to about a quarter of the usual length. For survival, it behaves as a recessive lethal: two copies usually stop development early in pregnancy. The Royal Kennel Club summarises it the same way on its T-box (bob tail) DNA test page: there are “no known health concerns” with one copy, while puppies with two “will likely die prenatally”.

SamSo the length of my dog’s stump tells me nothing about how many copies she has?

Elena MarshLength varies a lot among one-copy dogs. Hytönen’s group found no living dog with two copies among 360 tested, so in practice any natural bobtail you meet is expected to have exactly one.

Smaller litters, not sick carriers: the arithmetic of pairing two bobtails

There is no “carrier” in the usual sense here. A carrier of a recessive disease looks normal and passes on a hidden copy. A natural bobtail Aussie shows its copy on the outside. The breeding question is therefore not “is this dog a carrier?” but “what happens when two bobtails are mated?”

By simple Mendelian expectation, a bobtail crossed with a full-tailed dog gives on average 50% bobtail puppies and no double-copy embryos. A bobtail crossed with a bobtail gives, on average, 25% full-tailed, 50% bobtail and 25% double-copy conceptions. Those last embryos are the ones the UCL team described when they wrote that analysis of “several independent bobtail x bobtail crosses indicates that the homozygous phenotype is embryonic lethal.”

What does that cost in practice? The only measured figure comes from the Swedish Vallhund. In Hytönen’s survey, Vallhund litters with two short-tailed parents were 29% smaller than litters from parents without short tails. This number was measured in Vallhunds. Nobody has published the equivalent for Australian Shepherds, and it would be wrong to quote “29% smaller Aussie litters”. The direction of the effect is what transfers, not the size.

The rare exception matters too. “Two copies are never born” is not accurate. In a Norwegian Corgi study, two tailless newborns from bobtailed parents turned out to carry two copies, and both had anorectal atresia (no open anus) and multiple spinal defects. That is why UC Davis VGL’s published description, as indexed by search engines, warns that a BT/BT puppy born alive “may display severe developmental defects”, and why the RKC adds that such puppies, if born, die during or shortly after birth.

We found no US breed club or OFA guidance that formally advises against NBT to NBT matings, and OFA’s Australian Shepherd CHIC requirements (hips, elbows and an eye examination, with CEA and MDR1 DNA optional) contain no bobtail entry. The decision sits with the breeder and the stud owner.

SamIf litters can shrink, why would anyone deliberately pair two bobtails?

Elena MarshUsually to get more bobtail puppies without docking. The trade-off is what the Vallhund data showed: fewer pups overall, plus a small chance of the malformed newborns that Indrebø’s team described in Corgis.

N/BT, T/t, BT/bt and two coordinates: reading a report from any lab

Owners comparing paperwork from two litters sometimes think they are looking at two different mutations. They are not. The same variant is written in at least three genotype styles and at two positions.

Allele letters. UC Davis VGL, according to the search-engine listing of its Natural Bobtail page (the site refused our direct requests), writes the normal allele as N and the variant as BT, so a bobtail is N/BT. Paw Print Genetics, according to its own indexed test description, uses T/t, where capital T is the bobtail allele and t is normal; its page is currently a shell after the announced merger with Orivet, so we could not read it in full. Animal Genetics writes BT/bt. An N/BT from one lab, a T/t from another and a BT/bt from a third are the same result.

Coordinates. The 2001 and 2008 papers numbered the change as C295G; later work and OMIA number it c.189C>G, and OMIA’s entry 000975-9615 says outright that the earlier C295G mutation is “now called C189G”. The 106-position gap most likely comes from counting from the start of a cloned cDNA rather than from the start codon. The DogWellNet harmonisation database of the International Partnership for Dogs lists the Australian Shepherd “T Locus (Natural Bobtail)” test with c.295C>G at some providers and c.189C>G at others.

Wording slips. Even a seller’s page can contradict itself. Animal Genetics states that dogs with one or two copies “will have a natural short tail”, and in the next sentence that the BT/BT state “is lethal in utero”. Read the genotype, not the prose around it.

US prices seen on 18 October 2026, before any sales tax:

• Animal Genetics, Bobtail Gene / Short Tail: $40.00 (listed as “Breeds: All”; the page shows both 3-5 and 7-10 business day turnaround lines without saying which lab each applies to).
• Wisdom Panel Premium: $127.99 on sale (regular $159.99, or four payments of $31.99), results within three weeks; the panel includes a “Short Tail” trait located in the T-box gene, but the page does not name the variant or mention lethality.
• Genomia (Czech Republic), Short Tail – Bob Tail: USD 56.00 excluding VAT, 12 business days.
• UC Davis VGL: the test appears in its catalogue listing, but we could not confirm the current price or turnaround directly, so we do not quote one.

Whether Embark reports this variant for Aussies could not be confirmed.

Four inches, natural or docked: what AKC, ASCA and the AVMA say

The AKC breed standard, approved in May 1991 and effective from January 1993, reads: “Tail is straight, docked or naturally bobbed, not to exceed four inches in length.” The ASCA standard, created in 1977 and amended in June 2013, uses the same four-inch limit and calls the “natural or docked bobtail” an identifying characteristic. (ASCA’s own site blocked our requests; the text was read from a breeder site reproducing it.) Neither club ranks one origin above the other.

Veterinary policy points the other way. In November 2008 the American Veterinary Medical Association changed its policy, as reported by dvm360, that it “opposes ear cropping and tail docking of dogs when done solely for cosmetic purposes” and “encourages the elimination of ear cropping and tail docking from breed standards.” We could not load the current policy page on the AVMA site, so whether the wording has since changed is unverified.

State law adds detail. Pennsylvania, per an AKC legislative alert, allows owners to dock tails only on puppies under five days old; after that a veterinarian must do it, and a record of the vet, date and place must stay with the dog while the wound heals.

In this setting the DNA result has a specific use: it documents which of the two acceptable routes produced a given dog’s tail. For buyers who prefer an undocked puppy, an N/BT result on a bobtailed pup supports the breeder’s claim; in a purebred Aussie, an N/N result on a short-tailed pup strongly suggests the tail was shortened after birth (other short-tail mechanisms exist in some breeds and mixes, so confirm parentage and, if in doubt, retest).

Why a short tail on an English Aussie needs paperwork

England draws the line much more tightly. Section 6 of the Animal Welfare Act 2006 makes docking an offence, with an exemption for a “certified working dog that is not more than 5 days old”. The Docking of Working Dogs’ Tails (England) Regulations 2007 then define which types count: hunt point retrieve breeds, spaniels and terriers. Herding breeds such as the Australian Shepherd are not among them. Scotland and Wales have their own rules, which we did not review here.

The consequence is straightforward. An Aussie with a short tail born and raised in England cannot have been lawfully docked under the working-dog route, so the owner of a natural bobtail may want to be able to show it. That is a stated selling point for some labs: Animal Genetics says its test can identify whether a tail is naturally short or docked. UK options seen on 18 October 2026 include Animal Genetics at GBP 27.00 and LABOKLIN UK’s “Brachyury (Bobtail Gene / Short Tail / T-Box)” test at GBP 48.00 including VAT with a two- to three-week turnaround, which names the Australian Shepherd on its breed list. The Royal Kennel Club records results of its T-box (bob tail) DNA test, so a result can sit on the dog’s official record.

SamIf I import a docked Aussie into the UK, could the test prove anything about the docking?

Elena MarshIt can only say whether the dog has a natural bobtail genotype. In a purebred Aussie, a dog without the variant almost certainly had a full-length tail at birth; the RKC’s own guidance shows how results are recorded, but legality abroad is a separate question.

Adult bobtail spines: what Norwegian radiograph studies found

A common worry is that a bobtail Aussie will have a bad back. The evidence on adult one-copy dogs is limited, but it does not support a blanket claim. At the Norwegian School of Veterinary Science, Indrebø and colleagues (2008) radiographed 19 adult natural bobtail Pembroke Welsh Corgis from bobtail-to-long-tail matings. None had congenital spinal defects. The authors considered the short tail probably not associated with such defects in one-copy dogs, while noting that docking bans were making natural-bobtail breeding more common.

A larger 2026 study adds nuance. Berg and colleagues at the Norwegian University of Life Sciences reviewed hip-screening radiographs of 1,679 dogs from the Norwegian Kennel Club: 744 Brittanys and 935 Danish-Swedish Farmdogs. Lumbosacral transitional vertebra (LTV), a variant shape of the vertebra where the lower back meets the pelvis, was seen in 47.8% of Brittanys and 14.9% of Farmdogs. In Brittanys, bobtail dogs had about twice the odds of LTV (odds ratio 2.04, 95% CI 1.47 to 2.85), strongest in stump-tailed dogs. In Farmdogs the association (odds ratio 1.66) did not reach significance.

Three cautions keep this in proportion. The tail was judged on the X-ray, and genotyping is not reported in the publicly available abstract. It is a cross-sectional association, not proof that the variant causes LTV. And neither breed is the Australian Shepherd. The fair reading is that a natural bobtail is not shown to be a disease in adult dogs, and that a full-tailed result does not certify a normal spine either: the test looks at one letter of one gene.

A tailless newborn that cannot pass stool: the vet pathway and the insurance question

The situation that needs urgent action is rare but recognisable. The Merck Veterinary Manual’s image of sacrocaudal dysgenesis shows a tailless puppy with a typical posture and a radiograph in which the sacrum and tail vertebrae, and the nerves that should run through them, never formed, with a meningocele (a protruding sac of spinal membranes). Embrace’s pet-health page on the condition lists hemivertebrae, spina bifida and sacrocaudal agenesis or dysgenesis among malformations linked to taillessness, and notes that most animals with the trait show no ill effects. Those that do usually show it within the first few weeks: trouble using the hind legs, leaking urine or faeces, or both.

In an NBT to NBT litter, watch for a puppy with no tail at all, no visible anal opening, failure to pass meconium, a swelling over the lower back or weak hind legs. An absent anal opening is an emergency. Call the attending veterinarian immediately, before arranging any DNA test.

The usual work-up starts with a neurological examination and then imaging. Embrace mentions X-ray, myelography, CT and MRI. A 2023 case report from the University of Parma, describing two littermate Boxers with tail stumps and incontinence, shows the sequence in practice: exam findings such as an atonic anal sphincter and absent perineal reflex, followed by CT that confirmed partial sacral agenesis. Boxers are not shown to carry c.189C>G, so that report is a model of the investigation, not a TBXT case. Your vet decides on referral to a neurologist or surgeon; a DNA result supports, but never replaces, imaging.

Insurance logic here is unusual. Insurers define congenital conditions as those present at birth; the public FAQ pages of Trupanion and Healthy Paws describe them this way, as far as we could read excerpts of pages that blocked direct access. A malformation that is visible on day one exists before any policy can begin, so it is treated as pre-existing almost by definition. For a healthy one-copy adult, the tail is a breed trait rather than a condition; we found no policy wording that addresses later spinal claims in natural bobtails, so ask the insurer in writing.

Frequently asked questions

Q. Does a natural bobtail Aussie need a DNA test at all?
Not for its own health. The value is in breeding decisions, and in documenting that the tail is natural. A result is genetic information about one variant, not a diagnosis; health questions belong with your veterinarian.

Q. Can two bobtail parents produce full-tailed puppies?
Yes. Each bobtail parent has one normal copy, so by expectation about a quarter of conceptions inherit two normal copies and grow full tails. About half are expected to be bobtails, and the remaining quarter are the double-copy embryos that usually do not survive.

Q. Is the 29% litter reduction true for Australian Shepherds?
That figure was measured only in Swedish Vallhunds with two short-tailed parents. No equivalent Aussie figure has been published. The direction of the effect is expected to be similar; the size is unknown.

Q. My report says T/t and my friend’s says N/BT. Are these different genes?
No. Labs use different letters for the same TBXT variant, and some still write its position as c.295C>G instead of c.189C>G. Both describe a dog with one bobtail copy.

Q. If my Aussie tests N/N, is her spine guaranteed normal?
No. The test looks at one position in one gene. Spinal shape is assessed on radiographs, and lumbosacral transitional vertebra, for example, also occurs in dogs with full tails. Ask your vet if back or gait problems appear.

Q. A newborn in our litter has no tail and seems unable to pass stool. What should we do?
Contact a veterinarian immediately. A missing anal opening or hind-limb weakness in a newborn needs examination and imaging, not a DNA test first.

References

• Hytonen MK, Grall A, Hedan B, Dreano S, Seguin SJ, Delattre D, Thomas A, Galibert F, et al. (2009). Ancestral T-box mutation is present in many, but not all, short-tailed dog breeds. J Hered 100(2):236-240.
• Haworth K, Putt W, Cattanach B, Breen M, Binns M, Lingaas F, Edwards YH (2001). Canine homolog of the T-box transcription factor T; failure of the protein to bind to its DNA target leads to a short-tail phenotype. Mamm Genome 12(3):212-218.
• Indrebo A, Langeland M, Juul HM, Skogmo HK, Rengmark AH, Lingaas F (2008). A study of inherited short tail and taillessness in Pembroke Welsh corgi. J Small Anim Pract 49(5):220-224.
• Berg JA, Saevik BK, Lingaas F, Trangerud C (2026). Association between the natural bobtail phenotype and lumbosacral transitional vertebra in Brittany dogs and Danish-Swedish Farmdogs. Can Vet J 67(8):882-888.
• Xu X, Sun X, Hu XS, Zhuang Y, Liu YC, Meng H, Miao L, Yu H, et al. (2016). Whole genome sequencing identifies a missense mutation in HES7 associated with short tails in Asian domestic cats. Sci Rep 6:31583.
• OMIA 000975-9615: Tail, short in Canis lupus familiaris (dog). Online Mendelian Inheritance in Animals, University of Sydney. Accessed 2026-10-18.
• NCBI Gene ID 403653: TBXT T-box transcription factor T [Canis lupus familiaris]. National Center for Biotechnology Information. Accessed 2026-10-18.
• The Royal Kennel Club. DNA test – T-box (bob tail). Accessed 2026-10-18.
• Genomia s.r.o. (Pilsen, Czech Republic). Testing of dogs: Short Tail – Bob Tail. Accessed 2026-10-18.
• LABOKLIN UK. Brachyury (Bobtail Gene / Short Tail / T-Box), test ID 8219. Accessed 2026-10-18.
• Animal Genetics. Bobtail Gene / Short Tail. Accessed 2026-10-18.
• Wisdom Panel. Wisdom Panel Premium product page. Accessed 2026-10-18.
• DogWellNet / International Partnership for Dogs. Harmonization of Genetic Testing for Dogs: Tail length – short (Australian Shepherd). Accessed 2026-10-18.
• American Kennel Club. Official Standard of the Australian Shepherd (approved May 14, 1991; effective January 1, 1993).
• dvm360. AVMA denounces ear cropping and tail docking for cosmetic purposes (2008).
• The Docking of Working Dogs’ Tails (England) Regulations 2007, Schedule 1. legislation.gov.uk.
• Embrace Pet Insurance. Sacrocaudal dysgenesis. Accessed 2026-10-18.
• Dell’Apa D, Fumeo M, Volta A, Bernardini M, et al. (2023). Case report: Sacral agenesis in two boxer dogs: clinical presentation, diagnostic investigations, and outcome. Front Vet Sci 10:1201484. doi:10.3389/fvets.2023.1201484.

About the author

Elena Marsh

Editor & writer (not a veterinarian)

A writer with a molecular-biology background and a lifelong dog and cat owner. Not a veterinarian — she translates peer-reviewed genetics research and primary data into plain language, always as information rather than diagnosis.