Vertebral Column Defects

Vertebral Column Defects
In the Australian Stumpy Tail Cattle Dog

Selection for any tail, back or head abnormality (from the average normal) is simulataneously a selection for a "midline defect".The dorsal midline of a developing foetus is where the subsequent head, brain, spinal chord and vertebral column arise.

Short/Screw/Stumpy Tails
The selection of the shortening of a tail whether straight or screw tail is selection for a spinal defect as opposed to a straight, normal length tail. This similarly affects Manx cats.
Selection for sacro-caudal agenesis (short tail/no tail) is associated with an increased incidence of spiral dysraphism.

Spiral Dysraphism.
Refers collectively to a group of abnormalities involving the spinal chord, vertebral column and skin subsquent to faulty closure of the neural tube (developing spinal chord). This results in a group of 5-6 different conditions of varying severity, of which Spina Bifuda and Hemi Vertebrae are the most commonly seen defects.

Spina Bifida.
Is a condition where the neural tube(spinal chord) has not fully closed over so that the spinal chord is exposed along a section of the back. In these puppies, the vertebral column arch has not closed, neither has the skin. These puppies ar euthanised at birth.

Brachycelphaic(short head) breeds.
The selection for a shorter head, particularly a shorter muzzle, increases the influence of another midline defect, namely cleft palate and the associated hair lip. Cleft palates can also occur occassionally in any normal headed breed, with the incidence in long headed breeds (Dolciocephalic breeds)being extremely low.

Cleft Palate.
Is where the two sides of the roof of the mouth have failed to join during development and is either noticed at birth or within 2-3 days as the puppy can not suckle(no pressure flatter as the mouth is open to the nasal cavity) and milk comes out the nose. Failure of the lips to similarly close causes "hair lips."

Dolciphalic Breeds.
Longheaded breeds. This is associated with a skull. Flatter skulls usually result in a higher incidence of eye defects and an associated increased incidence of "Small Eye"(micropthalmia), seen also in cats.

Walrus Puppies.
While this is not in itself a vertebral column defect, it is most commonly seen associated with a combination of vertebral column defects. It appears that various combinations of two or more of the following: brachycephalic head, short body length and/or abnormal tail length, leads to a higher incidence of walrus "fluid" (anasarca)puppies in breeds so affected.
Walruss puppies are almost twice the size of normal puppies due to enormous fluid retention under the skin.Often these puppies have further abnormalities, particularly cleft palates.These puppies, invariably due to their size,result in ceasarean births.Breeds more commonly affected include British and French Bulldogs and Pekeingese.
In breeds where there are high incidences of walrus puppies, a simple recessive inheritance pattern has been postuated. Walrus puppies can still appear randomly in more "normally shaped" breeds, but the incidence is usually extremely low.

Short/Screw Tail Genetics
Sailer-1954 - considered there were 5 different inherited tail abnormalities. As many breeds are differentiated by their tail length and carriage, specualtion as to the finer points of the genetics of inheritance of many of the aspects including tail lenght, carriage etc are still very open. The inheritance of the Stumpy's short tail is considered to be caused by aln autosomal dominant gene with incomplete penetrance. Selection for this gene pattern when it occurred in a group of Beagles, lead to fewer caudal vertebrae (i.e. shorter tails) and line breeding of these dogs produced cases of Spina Bifida

Short/Screw Tail Genetics
As opposed to screw tails)were divided by Pulling (1957) into two groups.

Tail-less (anuary) or

Short Stub Tail (brachyury)

Selection for excessive shortness of tail would be expected to eventually increase the incidence seen of anal atresia (no anus).This is a separate condition to spinal abnormalities.
Screw tails (Stockard 1941) as seen in English and French Bulldogs was agin divided into two possible components.

Screw tail gene which is dominant and

Length of tail with long screw being dominant to short.

This is still not fully determined but seems likely.

Dermoid Cyst/Sinuses

As a point of interest,while not a vertebral column defect, the selection "1", or another midline defect of an abnormal pattern of skin lay along the back as seen in the Rhodesian Ridgeback, increases the incidence of dermoid sinuses/cysts. Dermoid sinuses are a neural tube defect resulting from incomplete separation of the skin and neural tube during development. The sinus of skin tissue runs to attach onto the tip of the vertebrae and in some cases, especially posterior (pelvic regions) may attach directly to neural tissue. This is considered to be inherited in an autosomal recessive mode.

Karen Hedberg
BVSC
January, 1999.

References:
Hoskin's Veterinary Pediatrics 1990
Willis Genetics of the Dog 1989
Clark and Stainer Medical and Genetic Aspects of Pure Bred Dogs 1983

Submitted by Bernadette Merchant