It comes from the catahoula !

good reference articles are on cats ceasle catahoula www.
http://www.bconnex.net/~langevin/html/bobtail_info.html Member of the “Natural Rearing Breeders Assoc.”
The bobtail trait is inherited as a dominant gene. Only one bobtail parent is required in order for bobtail pups to be whelped. On average, when breeding 1 bobtail parent and 1 longtail parent, 50% of the pups in the litter will have a bobtail.
The bobtail gene can not be inherited as “homozygous”. Meaning that a bobtail dog can not carry two bobtail genes (one inherited from each parent).
The bobtail gene is inherited as “heterozygous”. Meaning that a bobtail dog has 1 bobtail gene and 1 longtail gene.
Therefore when breeding two bobtail dogs together, there will still be both longtail and bobtail pups in the resulting litter. On average there should be 50% bobtail pups with this breeding.
The bobtail gene in Catahoulas (as with most other Cur breeds) has a “variable expression”, meaning that the length of the bobtail can range from a very short stub to a ¾ length tail, although on the average the bobtail is from 1 – 3” in length.
A longtail dog from a bobtail parent will not produce any bobtail pups when bred to another longtail dog. If a pup does not inherit a bobtail gene from a parent then the trait is forever lost in that pup...it can not be passed on as a “recessive” trait.
Out of eight associations, only the NALC faults the natural bobtail.
The Animal Research Foundation was the first to register the Catahoula in 1951. The bobtail dogs have always been included in their standard.
Note: Mr. Vernon Traxler was the first to registered a bobtail Catahoula with the ARF.
Mr. Traxler - “Traxler Catahoulas” had been breeding bobtail Catahoulas since 1944. His first bobtail Catahoula was acquired in a trade with the Indians at Three Rivers, south of Jonesville, LA - a yellow, glass eyed female.
When the NALC started up in 1975, the bobtail trait was not faulted. This fault did not come into effect until 1985. In 1995 the standard was revised to make the bobtail a serious fault.
Most Cur breeds have the natural bobtail trait. This trait is accepted by the various Cur breed clubs and organizations.
Remembering Bobtails
by David Traxler
David Traxler is the son of Vernon Traxler, an “old-timer” in the world of Catahoulas.
For more information on Vernon Traxler see Tribute
The first one I ever saw was when I was 6 years old. I walked out the back door and there he was. Almost as tall as I was, kind of gray-black with dark black spots all over. He had a white patch on his chest and no tail. Both eyes were brown with lines of white running through them. Almost as if they were divided like a pie. Part of his left ear was gone, and an ugly scar ran from the back of his head, over his ear, almost to the end of his nose.He had encountered a large wild boar when he was still a pup, and obviously the boar had won. There had been many battles with wild hogs as well as black bear since then. Old Bob wore many scars.
I would waste away the hot summer afternoons of my youth laying in an old swing in the backyard. Bob would lie next to me. While my grandpa would scratch my back, I would scratch Bob. As my little fingers would discover a scar on Bob, I would raise up, take a long look at it, turn to my Grandpa and ask, " What happened here Papaw"? Then as my grandpa would start the story, I would lay back down, close my eyes, and dream of the great hunt my grandpa and Bob were about to go on.
They all started the same. He got his first Catahoula from his grandpa when he was about my age. His grandfather had settled at the mouth of the Red River where it dumps into the Mississippi. He had married a half French/ half Choctaw Indian woman and they had a trading post as well as a ferry to cross the rivers. For a small fee, he would put up travelers, ferry them across one of the rivers, or trade them something. One fall, he traded 10 pounds of salt and a ferry across the Mississippi River to an old Catahoula Indian, for a white female cur. She had light blue eyes, several dark spots on her hips, three legs and was pregnant. She had seen her better days, especially since a black bear had torn off one of her front legs at the knee. Since the Indian had to cross the river before high water, and he had several other dogs, with winter coming on, and thinking that she would not be able to raise the pups or hunt, she could be traded. On the other hand, my great great grandfather needed a dog and since she was heavy with pups and bred to a half-red wolf/ half cur male that the Indian had with him, the deal was made.
Every winter, when high water came, everything was put on the ferry, and they waited out the flood. They felt this was better than moving to high ground because they always found a lot of stuff floating down the river and he could still trade with the people going down river to New Orleans. As fate was back then, winter came early and they moved on the ferry before the old female had her pups. Two weeks later she had four puppies. One died the next day, the other three lived. One blue female was traded the following spring to a Choctaw Indian for two pigs, one red female was traded to a half breed for a white female, and the other, a black leopard male with a white chest a partial glass eye and no tail was kept and named Bob.
So was born the ancestry of the present day Bob.
My ancestors as well as Bob's enjoyed many great hunts. I got to hear all this every time before Grandpa would tell me how Bob got the cut that made the scar. The rest of the story seems to fade from memory but the one thing that they all had in common was that Bob made a mistake and paid for it with some kind of a cut. Once I ask my grandpa if he and Bob had ever been on a hunt that Bob did not get cut. "Sure they did," he said with a half smile, but that was the easy hunts, and they seem to be forgotten in time. That's the way they are supposed to be. Any dog could make the easy hunts; it was the hard ones that you work for that would always be remembered. Each one of those scars was lessons in Bob's life that he had learned. Any dog could survive the easy hunts; it was the hard ones that made him good. The trick was to not only being there for the hunt but survive for the next hunt also.
It was not easy being a Catahoula Cur. Not only did they have to catch the animal; they had to catch them in such a way that they would live to hunt another day. These things were not taught, they were learned by instinct and by mistakes. When I got my own Bob and hunted the same swamps that Bob's ancestors and mine had hunted, I encountered many, many wild animals. Sometimes Bob couldn't hold them for me. Sometimes he would not catch them when I wanted him to. Sometimes I would become angry because Bob let them get away. As I got older, I realized just how good Bob was. He survived all those hunts as well as my temper so he could hunt again.
Bob gave me a lot of good memories; I cried the day he died. I buried him in an old Indian mound close to where Choctaw Bayou runs into the Tensas River. Maybe I'm crazy for spending so much of my youth on the back of a horse in a Louisiana swamp with a dog. Before he died, Bob gave me many things. Patience, Understanding and Perseverance were among them. And how to survive and hunt again!
That was many years ago and I thought this was the end of the story….I did not think I would ever own another Catahoula; not after Bob. But the spring of 1999 would bring me back to my youth. While playing on the Internet, I found a web page by Don Abney. My parents had lived next door to Don for many years in Abita Springs, Louisiana. One thing led to another and I ended up at Mary Langevin's web page. There on the Internet was a dog that looked exactly like my old dog, Bob! I waited for what seemed like ages, but was really only a few months, for my bobtail pup to be born. He will remember the many great hunts that I went on with my first Bob and the many great hunts of our ancestors. The smells of a swamp, the scent of a trail, the loyalty for his master; he will already know these things, for all this knowledge has been passed on to him.
His name will be Bob.