For interesting information on a parallel study in another breed, check out the Bobtail Catahoula Association web site.

"The mission of the Bobtail Catahoula Association is to preserve and maintain the genetic
heritage of the bobtail trait within the Catahoula breed, through education
and responsible breeding practices.

Our Primary Goals

To establish an understanding of the bobtail trait in the
history of the breed and the mode of genetic inheritance of the gene.

To collect and record data and statistics on bobtail pups whelped in litters
and to monitor these pups and any future generations they may produce."

A litter with varying tail lengths.  L to R: 1) tail not visible, 2) 1/4 tail, 3) very short NBT, 4) very short NBT, and 5) full tail.

How is the natural bobtail (NBT) gene in Australian Shepherds inherited?  Are there any health concerns associated with its occurrence?  And what effect will laws in various countries banning tail docking and the breeding of NBT individuals together have?  There has been a great deal of speculation and dispute, but no solid, scientific answers regarding the NBT gene in this breed.   

This study looked at data to find out about the percentage of NBTs in the breed, litter size in general and in relation to the presence of the NBT gene, and the incidence of neonatal defects.  With the data generated and pedigrees provided, this will give us clues as to the heritability of the NBT gene.  

An Australian Shepherd with a natural bobtail (undocked).  This bitch, when bred to a dog born with a full tail, produced a litter of 8: 3 very short tails left undocked, 3 tails 1/4 to 1/2 in length and 2 full tails.

The  bobtail is a naturally occurring trait in Australian Shepherds, although the exact mode of inheritance of this trait is presently unknown.  Some Aussies are born with full tails, some with none at all and some with partial tails.  Technically, a dog born with anything less than a full length tail has a natural bobtail (NBT).  The ASCA breed standard calls for a natural or docked bobtail, 4" or less in length.  Common practice has been to dock those tails shortly after birth which would be more than a few inches in length when full grown.  

In recent years, the number of countries which have banned the docking of tails has increased.  Some have also prohibited the breeding of one natural bobtail to another natural bobtail.  The reasoning behind this latter mandate is because there are breeds of dogs (Bulldogs) and breeds of other species (Manx cats) where taillessness is associated with an increase in spinal defects.  However, other breeds of dogs such as Pembroke Welsh Corgis have NBTs and no known spinal abnormalities are linked to the trait.

So, as American breeders are increasingly approached with requests from breeders in European countries - some wishing for a pup with a very short NBT and other requesting a long-tail pup from two long-tail parents - what effects this might have on the breed population as a whole in the long run?  Certainly, in the U.S. where docking is routinely performed, whether or not a dog is NBT is normally not a factor when deciding which specimens of the breed to continue with.  But now in Europe, we have some breeders selecting away from the NBT, whether through individual preference for a full tail or due to restraints in breeding options.  Conversely, other European breeders may opt to try to preserve the NBT as the identifying characteristic within the breed that it is. 

But what happens when such laws reduce a breeder's options?  What might have been the best choice in stud dogs for a certain bitch is not allowed because both individuals are NBTs.  The breeder is then forced to find a stud less suitable that has a full tail.  Or perhaps the breeder wishes to import breeding stock that is not closely related to what is already present in their country and has particular needs; however, the breeders they would like to select a dog or pup from are not willing to leave tails undocked, and so then the European breeder is forced to either give up on bringing in new bloodlines from America or must choose from some other kennel which may not suit their needs as entirely as the original choice.  A gradual drifting away from NBTs in the breed population begins to occur in certain countries and eventually the number of representatives of unique bloodlines where the NBT is prevalent become fewer and fewer.  Theoretically, this could lead to the possibility that the gene pool will be skewed towards those lines that do not typically carry the NBT, meaning less genetic diversity.  And genetic diversity is essential when a breed finds itself increasingly beset by genetically inherited diseases.

A young Aussie with a full tail

Two basic questions arose when I embarked on this quest for knowledge.  First, just how is the NBT in Aussies inherited?  Is it a dominant trait with incomplete dominance, meaning that a pup only has to inherit the gene from one parent, but may still show any length of tail?  Is it a recessive trait, meaning the pup has to inherit it from both parents?  

The second question was - is there in fact a possibility of spinal defects, such as spina bifida, associated with the trait in this breed?  And if so, is the incidence frequent enough to merit the prohibition of breeding two NBT individuals together?  

The final article in the study (link above left) provides some answers to that.  In short, a test does exist that can tell us if the NBT gene in our Aussies is the same one as that in Pembroke Welsh Corgis, although to date this test has not been performed on any Aussies with a NBT.  Secondly, although this study was relatively small, there were no spinal defects in any of the litter data contributed.  There were a few incidences of imperforate anuses; however, in relation to the total number of litters/pups studied the occurrence of this defect is negligible.  Overall, the presence of the Natural Bobtail trait in Australian Shepherds should not be regarded as a defect, nor should there be unwarranted concern about the breeding of two otherwise complimentary bob-tailed individuals together, if all other desirable traits are present and the parents' health clearances are acceptable.