This article was published in the Australian Veterinary Journal Vol 74, No. 1, July 1996

Have an understanding of the purpose of the Canine Tail prior to any drastic decision to have it removed from a PF dog. Although this article makes reference to docking, the function of the tail remains the same.

ANATOMICAL CONSIDERATIONS.

An understanding of the importance of the tail and the con- ditions to which docking can predispose is gained by reviewing the anatomy and the physiology of the tail and the pelvic region. The canine tail usually consists of 20 (6 to 23) highly mobile vertebrae largely enclosed by a very versatile musculature making the various segments, especially the tip capable of finely graded movements. Part of the musculature is formed from muscles associated with the rectum, the anus, and the pelvic diaphragm. The tail is served by 4 to 7, paired coccygeal nerves. On leaving the spinal canal the branches of these nerves anastomose to form the left and right dorsal and ventral coccygeal trunks which lie on their respective surfaces of the transverse processes of the vertebrae. The dorsal muscles of the tail are direct continuations of the epiaxial musculature of the trunk. The dorsal sacrococcygeal muscles are extensors, while the sacrococcygeus ventralis later- alis and medialis muscles act as flexors or depressors of the tail. These muscles have many tendons that insert from the 5th or 6th coccygeal vertebra then onto the next vertebra and so on to the end of the tail. The coccygeus, levator ani, and the inter- transversarius caudac muscles are lateral flexors of the tail. The rectococcygeus muscle is composed of external fibres from each side of the rectum with the left and right portions fusing at the level of the 3rd coccygeal vertebra then inserting on the 5th and 6th coccygeal vertebrae. This attachment on the tail serves to support, anchor and stabilise the anal canal and the rectum, preventing them from being pulled cranially by a peristaltic wave. By its contraction, the rectococcygeus muscle can move the anal canal and rectum caudally thus evacuating faecal material (Miller 1969).

The pelvic diaphragm is the vertical closure of the pelvic cavity formed by the coccygeal muscles. The coccygeal muscle originates on the ischiatic spine, extends to the lateral surface of the tail and inserts on the 2nd to 5th coccygeal vertebrae The levator ani muscle (m coccygeus medialis) originates on the ilium, pubis and pelvic symphysis, radiates upwards sur- rounding the genitalia and the rectum and ends on the 4th to 7th coccygeal vertebrae. Besides helping to contain the con- tents of the pelvic cavity the levator ani muscle moves the tail cranially and laterally, presses the tail against the anus and the external genitalia, compresses the rectum and causes the sharp angulation between the 6th arid 7th coccygeal vertebrae which is characteristic for defecation. Only in carnivores does the levator muscle reach the vertebrae of the tail, thus the detri- mental effect of tail docking on the role of this muscle will be more significant in the dog compared with other domestic species.

PHYSIOLOGICAL ASPECTS.
LOCOMOTION.

The tail is important as a means of counter-balance when the dog is carrying out complicated movements such as leaping, walking along narrow structures, or climbing. Tail muscles are also important in stabilising the vertebral column and sup- porting the action of the extensor muscles of the back as well as those of the croup and buttocks.

DEFECATION.

Normally the rectum, anus, and anal canal are devoid of faecal material with the walls in apposition. During defecation the dog assumes a squatting position with elevation of the tail and subsequent relaxation of the coccygeus, the levator ani, and the rectococcygeus muscles. This allows the migrating contractions in the colon to push the faeces distally into the rectum with defecation ensuing. The movement of the tail during the act of defecation has a direct influence in evacuating the rectum and anal canal of the last part of the faecal bolus. The coccygeus and levator ani muscles cross the rectum laterally tending to compress the tube, while the rectococcygeus shortens the tube. After defecation the muscles return to their normal position with concomitant obliteration of the empty lumen. If the tail is removed from an immature puppy the muscles of the tail and pelvis may fail to develop to their full potential. Removal of the tail in the mature dog may lead to atrophy and degeneration of these muscles, in addition, if these muscles lose their distal attachments there may be a lessening of the support and anchorage of the rectum and anus. An absence of adequate function of these muscles may result in rectal dilata- tion, rectal sacculation and faecal incontinence.

PELVIC DIAPHRAGM INTEGRITY.

Perineal hernia involves a breaching of the caudal wall of the pelvic cavity with herniation of the rectum, the abdominal contents or the pelvic contents through an opening bordered by the anal sphincter medially, the coccygeal muscle laterally and the internal obturator ventrolaterally. Any process result- mg in fascial weakening, muscle atrophy, or muscle degenera- tion may predispose to this weakness in the pelvic diaphragm. Often perineal hernias occur secondary to medical conditions which cause tenesmus with resultant weakening of the pelvic diaphragm.

ACQUIRED URINARY INCONTINENCE.

Urinary incontinence in bitches caused by urethral sphincter mechanism incompetence (SMI), is a multi factorial condi- tion. A recent study (Holt and Thrusfield 1993) noted the increased risk of SMI developing in large breeds but it also concluded that bitches belonging to small breeds had a reduced risk and medium breeds had no increased risk. Breeds identified in this study as having significantly increased risk of developing SMI were the Old English Sheepdog, Rottweiler, Doberman Pinscher, Weimaraner and Irish Setter. A reduced risk was demonstrated in the labrador retriever, and, although the result was not statistically significant, a low risk was observed in the German shepherd. This agreed with the obser- vations of Arnold et al (1989). Holt and Thrusfield (1993) noted 2 consistent association between SMI and tail docking which they interpreted as an indication that docked breeds of whatever size are more likely to develop incontinence than undocked dogs of the same breed. It is well recognised in women that the risk of develop- ing genuine stress incontinence (GSI) is related to pelvic floor muscle damage during labour. In the bitch the equivalent 'pelvic floor' muscles are the levator ani and coccygeus muscles both of which attach to the tail base, and it is possible that these muscles are atrophied and/or damaged in docked breeds reducing urethral resistance.

CONCLUSION.

Unless pecuniary or traditional reasons are to take priority over the welfare of the animal, then the criteria to justify removal of a dogs tail are not satisfied. The tail is not merely an inconsequential appendage. It is an anatomically and physiologically sign significant structure which has many biological functions that should not he underesti- mated. Tail docking can predispose the dog to detrimental consequences including intense, initial pain and continuing pain related, neurological problems. Tail amputation should only be performed on those dogs whose tail or associated structures have been injured or where there is occult pathology of this appendage. If tail amputation is indicated as a therapeutic measure, appropriate anaesthetic and surgical techniques should be employed.

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Many people, some of them on this PF List who speak from personal experience, feel that the practise of tail removal on a PF dog is unwarranted. It either does NOT work or does NOT work well enough to warrant the emotional and physical pain as described aove.