Animals With No Tail
Taillessness, or "anury" may have a genetic basis, or occur through surgery or accident, or the effect of toxins. Also included are cases where they tail is present but much shorter than usual ("brachyury"). However they came to lose their tail, most of these creatures don't let it slow them down!
Tailess by Genetics
Genetic that bring about a shorter or missing tail are typically related to some degree to other deformities of the spine, hips and lower digestive tract. Thus unless the animal comes from a good breed or line known not to exhibit these problems, genetic taillessness should be considered a deformity.
Some breeds of chicken (called "rumpless") do not grow a tail. For example the Araucana Chicken. They are also known for their blue legs and and blue-shelled eggs. Rumplessness also seems to occur at a higher level if the eggs are shaken before incubation.
A number of dogs carry genetic for a 'bob' tail. The Old English Sheepdog was often born without a tail, but this trait was not selected for--so most dog of this breed now have their tail surgically removed to meet the breed standard. Now that surgical docking of dog tails is becoming less acceptable man breeds are trying to introduce or increase the rates of naturally bobbed genetics in their breed. One breed introduced the bobbed tail gene from the corgi into boxers and within a number of generations was able to produce naturally bobbed boxer show champions. And in countries where tail docking is not allowed owner have to acquire paperwork showing that their dog is naturally bobbed and was not illegally modified.
Natural bob tails also occur in the following dog breeds: Australian Shepherd, Austrian Pinscher, Australian Stumpy Tail Cattle Dog, Boston Terrier, Braque du Bourbonnais, Brazilian Terrier, Brittany Spaniel, Croatian Sheepdog, Danish Swedish Farmdog, English Bulldog, Jack Russell Terrier, Karelian Bear Dog, King Charles Spaniel, Miniature Schnauzer, Mudi, Parson Russell Terrier, Polish Lowland Sheepdog, Pyrenean Shepherd, Savoy Sheepdog, Schipperke, Spanish Water Dog, Swedish Vallhund and the Pembroke Welsh Corgi.
The Manx Cat
Manx cats come in long and short hair varieties, and in all common coat colors. They are distinguished by their lack of a tail. The Manx breed was developed in the United Kingdom based on a mutation that was common in cats from the Isle of Man.
There are also some more recently developed tailless cat breeds such as the Japanese Bobtail and the American Bobtail. Both of these do have a tail but it is about one third of the normal length for a cat. There are also some boutique mixes that have not really reached the status of being recognized breeds, such as the Mojave Bob.
Tailless (a.k.a. "Manx") is an accepted category of "fancy" or show rats. It may be confine with any other morphological and color types. Stub or stump tails are not consider acceptable.
The earliest records of tailless come from 1915 and originates from Eglish animals.The inheritance of the trait is not straightforward making breeding tailless rats a tricky prospect. Tailless rats should only be bought directly from a responsible and highly skilled breeder.
Tailless rats sometimes exhibit a range of deformities of the bladder and pelvis. Females are often sterile or have difficulty giving birth. Many breeder do not breed from a tailess female for this reason.
Tailless/manx mice seem to have a similar generic pattern however the inheritance may be closer to a simple dominant gene.
Tailess by Mis-Adventure
Many animals are like bird and lizards are designed to be able to lose a tail in order to escape a predator, and regrow it later. But most mammal experience pain, blood loss and risk of infection when losing part or all of a tail. And depending on the trauma and degree of lose they may suffer reduced agility, spinal damage or even lose the ability to defecate normally and become either constipated or incontinent.
New York Squirrels
Squirrels in the city can be prone to accidents that cause them to lose their tail.New York squirrels are particularly well-known for going tailless (see: Squirrel With No Tail). (Or perhaps that is just the fashion for the jet-setting urban squirrel...) But examples are seen in plenty of other places too (e.g. Charleston and Ontario)
Tails of various animals are docked either for human convenience or to achieve a certain look that is considered distinctive or stylish. Sometime a post hoc explanation is made that docking the tail it keeps the animal cleaner or protects them from injury--but in most cases the evidence does not back up these claims.
Cow tails used to be docked to elp keep the udder clean and prevent transmission of disease from the cow to the milker. However this practice has been shown to be ineffective and thus unecessary--and is largely obsolete.
On many farms the tila of piglet are docked short. This is because pigs can develop the habit of biting each others tails, and sometimes causing serious injuries.
Sheep tails are docked to prevent flea depositing maggot producing eggs underneath them in the sheltered "breach" area. But the should not be cut too short. Tails cut below the major tendons have a tendence to develop prolapses. Unfortunately the habit of cutting a sheep's tail completely off persists with show breeds because it is thought to make the rear of the sheep look broader and better for meat production.
Horses tails were traditional docked short to prevent tangling in harness when plowing or drawing a wagon, or sometimes because it was deemed to improve their cleanliness or appearance. This practice is now largely obsolete however you can still see it on some prominent draught teams like the Budweiser Clydesdales.
Tailless by Toxins
A number of substances can cause anury in offspring if the mother is exposed during pregnancy.
Some dewormers such as parbenzol can cause birth defects includng anury.
Toxins known to cause anury in offspring include indium.