Natural Bobtail in Chihuahuas
Bobtails in chihuahuas has had a surprisingly negative response by what seems to be folks lacking any knowledge about the breed. I have read about how they are not purebred or some even more bizarre references all over social media and the internet. As a long-time breeder and owner of a DNA-tested bobtail, I have some insights.
The natural bobtail found in the chihuahua breed has been present as we have written history about this breed. The Chihuahua Club of America allowed bobtailed Chihuahuas to be shown in the AKC up to the revision to the standard in 1972. Therefore today, the predominant number of bobtails produced will come from older show lines.
“Tail – moderately long, carried sickle either up or out, or in a loop over the back, with the tip just touching the back. (Never tucked under.) The hair on the tail in harmony with the coat of the body, preferred furry in smooth coats. In long coats full and long as in a plume. A natural bob or tailless is permissible if so born.” – Tressa Thurmer “ Pet Chihuahua copyright 1962.
The reason for the bobtail has a lot to do with the history of this breed. I will be blogging more about genetics and origin in another post. Right now, we know that the Chihuahua that we know today first appeared in the Americas in the early 1900s. We know that 99% of the Chihuahuas that have been DNA tested have NO relation to any Mexican or South American dogs (Xolo or Inca Orchid). We do know they are a mixture of many European breeds. The leading theory I have held since reading about them in the early 90s is that they are related to the Maltese dog named Kelb tal-But (Maltese Pocket Dog)
The condition that we thought caused a natural bobtail in chihuahuas, we now know it’s NOT responsible. In many breeds like Corgis, Bobtail is caused by the Brachyury mutation. The inherited trait is autosomal dominant, which means that dogs who carry one or two copies of the mutation will have a naturally short tail. Dogs with two copies of the normal non-mutated gene will have standard tail lengths. In the homozygous state, the Brachyury mutation is lethal in utero. For this reason, breeding two dogs with the bobtail gene reduces litter sizes.
Test to determine the number of copies of the recessive bobtail/short tail allele a dog carries. Dogs can be DNA tested at ANY age.
Recently we tested our bobtail to see if she had this form of natural bobtail. To our surprise, she did not have it. Her bobtail must be the cause of another natural bobtail gene we do not know of yet.
Lulu has a very short tail, about 2” in length. We know this is not the average tail length for most chihuahuas, and we would not call it normal. Lulu also has an uncle who has the same length of tail and does not have this form of natural bobtail.
Please let us know if you have a bobtail and have had it tested for the T-locus. We want to know if you have any questions or have found your bobtail has a natural mutation different from this.