Natural Bob Tail - NBT



NBT is a natural shortening of the coccyx or tailbone. The mutation in the gene for tail length causes a shorted tail or absence of tail to occur. When seen in the heterozygous condition, various levels of penetrance occur, from almost no tail to a shortened tail.

Severity - 1

NBT has a low degree of severity, as the trait itself poses no health concerns. However in the case of a homozygous dominant dog, the allele becomes lethal in the embryonic stage and the affected dog does not survive.


While a shortened tail has no pressing health concerns, and the gene mutation doesn’t appear to affect any other aspect of the dog’s health, breeding NBT dogs can be high risk. Natural Bob Tail is a dominant trait, that is a dog only requires a single copy of the NBT gene in order to express the trait. The problem arises when a dog is homozygous for the dominant gene, that is, they have two copies of the NBT causing gene. When a homozygous dominant occurs, the gene becomes lethal and the affected pup dies. Death of the homozygous affected dogs usually occurs in the embryonic stage, this usually accounts for small litter sizes among NBT’s being bred, as the homozygous pups do not survive.

Genetic Testing

Animal Network provides a DNA test that determines the genetic predisposition to NBT.

As NBT is a dominant trait, a single copy is required in order for a dog to be affected. There are no carriers of a dominant trait, clear dogs possess no copies of the NBT gene, while affects have one copy. A dog with two copies of the NBT gene will not survive.

Due to the autosomal dominant nature of the Natural Bob Tail (NBT) condition, it is advised that if breeding is to occur, dogs be tested in order to prevent the homozygous lethal allele occurring in pups.

For an explanation of possible genetic status of offspring please refer to our fact sheet on Breeding strategies. ORDER A TEST

Breeds Affected

Australian Shepherd
Australia Stumpy Tail Cattle Dog
Jack Russell Terrier
Old English Sheepdog
Swedish Lapphund
Tenterfield Terrier
Welsh Corgi Cardigan
Welsh Corgi Pembroke
Polish Lowland Sheepdog
Spanish Water Dog

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