Rotties tails are removed (docked) after birth.. they are born with tails..
Breeds have their tails docked for various traditional reasons, and it is part of the breed standard.. at one time,, it was more to do with a particular function, but today it has more to do with the look of a breed,, and is controversal as to if it should be done anymore, if it causes undue pain on newborns,, or prevents furture tail injury as adults..
Some breeds however do carry the gene for a naturally short tail, or are born without tails, or tails of various lenghts.. So in a litter you can get anything from no tail, to a full tail, and crooked, bent or straight tails.. this is a mutation, that breeders selected for.. either for a particular look, or use,, by man.. not a result of natural selection..
Often breeds that are docked do carry the bob tail trait.. But there has been a concern with breeding for a short tail specifically may be associated with other Spinal abnormalities.. So a short tail is preffered but if you purposly breed for it you can produce puppies/dogs with other problems.. so the rest are docked because the short tail is prefered..
although I am not 100% sure rotties are not a breed that carries the bob tail gene and I believe the tail was docked for a traditional specific reason.. they actually do have quite lone thin natural tails, and in a working/herding breed like a rottie, it may have come about because of problems when the dog was working and injuries to the tail as adults.. so breeders started to dock the tails at birth to prevent this problem.
Now granted most rotties are not pulling carts, herding livestock and guarding the farm today.. but the "look" and standard of the breed is one with a short tail.
Amanda
Amanda