Boxer Dog Short Tail. They are not just a short tailed version of an australian cattle dog. The genes for the shortened tail may be dominant or recessive.
It's part of the breed standard if you read the boxer breed standard according to the akc, you'll find that their tails are skip to content A tight rubber band is put around the tail, cutting off blood supply, which eventually causes tissue death the tail to shrivel up and fall off. An undocked boxer is even being penalized for not having a short tail.