Naturally Bobtailed (NBT) Dogs and Breeding Considerations

The Spanish Water Dog has, for many years, included naturally bobtailed (NBT) individuals within the population. These dogs are a recognised and established part of the breed, both in the UK and across Europe.

Preferences vary, with some favouring a full tail and others a shorter or absent tail, but this is largely a matter of type rather than welfare.

Is NBT a welfare issue?

At present, there is no published, evidence-based data demonstrating that a naturally short or absent tail compromises the welfare of Spanish Water Dogs^[3]. In practical terms, NBT dogs live normal, active lives without consistent reports of pain, dysfunction or health issues attributable to tail length.

Where discussion often arises is around breeding two NBT dogs together. The current scientific understanding is that this involves a gene known as the T-box (or brachyury) mutation^[1].

Embryos inheriting one copy of this gene may go on to develop into dogs with a shortened or absent tail.

Embryos inheriting two copies do not develop and are resorbed very early in gestation^[1].

Importantly, this early embryonic loss occurs before development progresses and is not associated with suffering in the bitch or live-born puppies.

There is no documented case of a homozygous (2 copies of the gene) NBT embryos developing past the embryonic stage^[1].

In live-born dogs, this mutation is not associated with vertebral malformations or clinical disease.

Where confusion has arisen

A significant source of concern appears to come from comparisons with other breeds, particularly brachycephalic breeds such as English Bulldogs, French Bulldogs and Pugs.

In these breeds, a different genetic mutation, known as DVL-2, is responsible for tightly curled “screw tails^[2]”. This mutation affects broader skeletal development and is associated with known health issues, including:

• spinal deformities
• pain and discomfort
• dermatitis around the tail^[2],[3]

This is a fundamentally different genetic mechanism, with different outcomes^[2].

By contrast, the T-box mutation seen in Spanish Water Dogs and similar breeds affects tail length only and does not carry the same associated health concerns in live-born dogs.

These two conditions are not phenotypically or genetically comparable, and should not be considered as part of the same issue^[2].

Why this matters for breeding decisions?

The UK population of Spanish Water Dogs is relatively small.

Maintaining genetic diversity is an important and ongoing concern for the long-term health of the breed.

Excluding NBT to NBT matings entirely removes a proportion of potential breeding combinations from an already limited gene pool. Over time, this may contribute to reduced genetic diversity, which is widely recognised as a greater risk to overall breed health than the controlled use of established traits^[4],[5].

Allowing breeders to make informed decisions, supported by current evidence, enables:

• Open discussion and transparency.
• Monitoring and documentation of outcomes.
• A more sustainable approach to population management.

Driving practices out of view does not support welfare or learning. Engaging with them does.

Belief, ethics and evidence

We recognise that individuals may hold personal views about breeding practices, including concerns about embryonic loss.

These perspectives are valid at an individual level.

However, it is important to distinguish between personal belief and evidence-based welfare concerns.

Ethical breeding decisions should be grounded in proportionate, evidence-led assessment of risk and impact across the population. Where there is no demonstrated harm in live animals and where restrictions may negatively affect genetic diversity, caution should be balanced carefully against long-term consequences.

Our position

As a Society, we support breeders in making informed, responsible decisions based on the best available evidence.

We do not consider NBT to NBT matings, in themselves, to represent a welfare issue in the Spanish Water Dog. We do, however, support continued observation, open dialogue and where possible, the collection of further data to ensure that decisions remain grounded in evidence.

Our aim is simple: to protect the long-term health, functionality and integrity of the breed, without imposing unnecessary restrictions that are not supported by current scientific understanding.

References

1. Haworth, K., Putt, W., Clements, D., et al.
Brachyury (T) mutation associated with natural bobtail in dogs.

2. Mansour, T.A., Lucot, K., Konopelski, S.E., et al. (2018)
A nonsense mutation in DVL2 is associated with screw tail in Bulldogs, French Bulldogs and Boston Terriers.
PLOS Genetics.

3. O’Neill, D.G., Skipper, A.M., Kadhim, J., et al.
Health and welfare studies in brachycephalic dog breeds.
VetCompass Programme, Royal Veterinary College.

4. Calboli, F.C.F., Sampson, J., Fretwell, N., Balding, D.J. (2008)
Population structure and inbreeding in pedigree dogs.
Genetics.

5. Royal Kennel Club
Breed health and conservation guidance, including the importance of maintaining genetic diversity in pedigree dog populations.
https://www.thekennelclub.org.uk⁠