Manx rats are tailless rats. Thier body proportion and conformation should ideally be identical to that of a tailled rat, with the subtraction of the tail. Because the tail of a rat is very important in both balance and temperature regulation, care should be taken with them. Manx rats may, like cats, be either completely tailless or "rumpy" or with a short tail or "stumpy." Some bloodlines of manx rats have had issues with spinal deformations such as spina bifida, and many breeders are reluctant to breed tailless females for fear of birthing problems. Usually, tailless bucks are bred to tailed does out of a manx line.

Manx does not seem to be a simple recessive. There have been cases of breeding a manx rat to his own daughters and not producing manx. There may be multiple forms of taillessness using different genes, and they may also be polygenetic, requiring more than one activated gene to express.

AFRMA

"Tailless rats may be shown in any recognized color, marking, or Variety. The distinct feature is the complete absence of a tail. Tailless rats may have a cobbier body and will have a rounded rump."

RSA

"Tailless to be shown in AOV.  To have complete absence of a tail, may have a cobbier body and rounded rump.  Disqualification: any evidence of physical abnormalities due to being tailless including walking, climbing, and skeletal problems.  Any evidence of a tail.  Docked tail."

RatsPacNW

"The tailless rat should not have points taken off for being too small.  When allowed to walk they should sit a little higher in the rear then most rats. Their spine should feel like it ends where the tail would begin (that is quite a bit farther then most people think) there should not be anything sticking out. You should be able to feel the last vertebrae in their spine.  A rat should not be docked for having a small piece of skin sticking out so long as their is no bone.   A tailless rat should be more rounded in body shape, not fat but the whole body should appear more rounded and shortened. Hind legs should be slightly longer then the front legs (not dramatically). The judge should have treats for this class, the rats should be able to stand on their hind legs with ease! Check the rear end for scars, if it looks like the rats tail was CUT off, they should be disqualified!

DQ: deformed or shuffles when walks."

URS

"There should be complete absence of a tail, giving the appearance of a cobbier body and a rounded rump.

Disqualification: Any evidence of a tail. Docked tail. Any evidence of physical abnormalities in walking, climbing, or skeletal problems."