Animals Without Tails

Many species of animals have genotypes that produce individuals with no tails. These are often used to study genetic processes, as the expression of the gene is easy to see in offspring. The welfare impacts vary across species but can be pronounced, leading to questions about the ethics of deliberate breeding.

Cats (Manx)

Manx cats have a dominant mutant gene (often called M) that disrupts normal development of the tail vertebrae; all true Manx are heterozygous for this mutation (Mm). Different, independent mutations in the same Brachyury (T) gene underlie abnormal tail length in several bobtail cat breeds such as Manx, Pixie‑Bob, American Bobtail, Kurilian Bobtail, and Japanese Bobtail. Breeding two Manx cats together typically results in kittens with spinal deformations.

Dogs ("Bobtail")

In many “natural bobtail” dog breeds, a mutation in the T gene (often described as C189G) shortens or removes the tail while leaving other dogs of the same breed fully tailed. This natural‑bobtail mutation has been documented in numerous breeds, including Australian Shepherd, Australian Stumpy Tail Cattle Dog, Pembroke Welsh Corgi, Brazilian Terrier, Croatian Sheepdog, Spanish Water Dog, and Swedish Vallhund. Several other bobtailed breeds (for example, Boston Terrier, English Bulldog, King Charles Spaniel, Miniature Schnauzer, Parson Russell Terrier, and Rottweiler) have inherited tail‑shortening mutations that are not the common C189G form, implying multiple independent mutant origins of taillessness.

Mice

In mice, tailless or very short‑tailed individuals are classic laboratory mutants, not the normal wild type; most are caused by genes that control early body‑axis and tail development. These mice were important in early genetic research. In the pet and show trade, mice with no tail or a shortened tail are referred to as "manx mice". However, tailless mice are not a standardized breed, and the mutations present in them are unclear. The lack of genetic knowledge in the pet trade is ironic given the prolific research on this topic in relation to laboratory strains.

Rats

Manx rats show not only a missing tail but also changes in the rear end. The genetic basis is unknown and harmful to health, associated with smaller size, breeding difficulties, and malformations that are sometimes lethal.

Sources

Conrow, S. B. (1915). Taillessness in the rat. The Anatomical Record, 9(10), 777-784.
Schulte-Merker, S., Eeden, F. V., Halpern, M. E., Kimmel, C. B., & Nüsslein-Volhard, C. (1994). no tail (ntl) is the zebrafish homologue of the mouse T (Brachyury) gene. Development, 120(4), 1009-1015.