(Conformation means physical size, shape and appearance of a dog)
These include the consequences of large or small body size, or small or large head size.
Large breeds, for example Wolfhound, are predisposed to disorders resulting from increased body size or faster rate of growth. A faster growth rate requires faster bone growth. An overproduction of calcarious matter may lead to a range of metabolic bone diseases such as osteochondritis dessicans
A greater body mass increases pressure on joints, leading to dysplasia and degenerative joint disease, the most common being hip or elbow dysplasia and cruciate ligament disease.
Conversely, small or miniature breeds suffer from conditions associated with small body size or short legs, for example, patellar luxation as a result of shallow patellar grooves (so the kneecap slides out) For example, Pomeranian.
Short legs are associated with Legg Calve-Perthe syndrome (lack of blood supply and destruction of the head of the femor, leading to osteochondrosis. Also multiple fractures caused by bone reduction.
A small head size relative to the size of the brain can cause Chiari malformation and Syringomyelia (Cavalier King Charles Spaniel).
The small head in miniature breeds leads to overcrowded teeth, retention of juvenile teeth and other dentition problems (Yorkshire Terrier).
A short head and nose (brachycephalia) causes respiratory problems, difficulties in cooling down in hot weather or after exercise, and exercise intolerance (Bulldog).
An overly short tail is linked to congenital spinal abnormalities and difficulties in communicating with other dogs (Pug)
Low tail carriage and broad tail base is linked to anal furunculosis (chronic and painful inflammation) (German Shepherd)
Screw tail breeds are at risk of spina bifida and hemivertebrae (wedge shaped vertebrae causing severe kinking of the vertebral column and spinal cord compression) (Pug)
Large and deep chested breeds are prone to gastric torsion (stomach dilates and twists around). An extremely painful and life threatening condition (Great Dane).
Brachycephalia (disproportionate shortness of the head) reduces a dog’s ability to breathe properly. The bones in the skull are shorter in length but normal in width. The soft tissues in the respiratory passages are not reduced in keeping with the reduced bones lengths, and the superfluous soft tissue narrows and obstructs the air passages. Obstructions include narrow nostrils, an overlong soft palate, enlarged and everted laryngeal saccules, malformed trachea. The combination of any of these is known as Brachycephalic airway obstruction syndrome (BOAS). BOAS can severely impact on a dog’s quality of life, reducing his exercise tolerance, affecting his ability to rest and his ability to cool down in warm conditions. Breeds affected are: Bull Dogs, Pugs, Boston Terrier, Boxer, Pekingese, CKCS, Shih Tzu, Shar Pei.
Tracheal collapse is associated with miniturisation (eg Miniature Poodle, Yorkshire Terrier, Chihuahua, Pomeranian). It involves the reduction of the diameter or the trachea – made worse by excitement, exercise, heat, obesity.
Dystocia, or difficulty giving birth, is linked to breeds with broad/large heads and relatively narrow pelvises. Breeds affected are: Sealyham Terriers, Scottish Terriers, West Highland White Terriers, Bulldog, Boston Terrier, Pug.
Urate urolithiasis (formation of uric acid stones within the urinary tract) is linked to coat pattern and colouration in Dalmatians.
Excessive skin folds are a common cause of canine ill-health. Dermatitis and pyoderma (causing irritation and infection) are commonly develop in dogs with excessive skin folds. Breeds affected are: Basset Hound, Bulldog, Shar Pei. The Shar Pei also suffers uniquely from cutaneous mucinosis (mucin helps to form thickened skin and these high concentrations of mucin build up over time causing blistering and inflammation).
Infections of the skin also predispose dogs to ear infections. Otitis externa is more common in breeds with factors that predispose them to skin infections.
Pendulous ears and excessive hair in and around the ear make the problem worse. Such ear conformation leads to humid and poorly ventilated ear canals, facilitating bacterial multiplication. Otitis media, associated with the CKCS, is caused by an accumulation of mucus in the middle ear. It results from overproduction of viscous mucus, and lack of aeration in the middle ear from inadequate drainage through the Eustachian tube.
Entropion and ectropion are disorders of the eyelid with the eyelid turning in to the eye (causing irritation) or sagging outwards (leaving the eye exposed), respectively. In some giant breeds, such as the Saint Bernard, both can exist, such that the central lower lid is ectropic while the lid at the corners is entropic (referred to as ‘diamond eye’). Two other conditions related to eyelid conformation are trichiasis (Pekingese) (an irritation caused by hair around the eye area) and eversion of the nictating membrane (prolapsed third eyelid), occurring in larger breeds with facial folds and a distinct stop. Eyes are exquisitely sensitive so all of these conditions can result in discomfort, pain and irritation and secondary conditions such as conjunctivitis, or corneal ulceration.
Rhodesian Ridgebacks suffer from dermoid sinus – a condition caused when the skin and neural tube do not separate entirely during development. Basically this is hole in the skin which can extend down towards the vertebral column, the implications of which depends on the depth of the hole. If shallow it can cause irritation from bacterial infections. If severe, meningitis or myelitis can result. It is linked to the distinctive ridge of backward growing hair along the spine.
Dogs with protruding eyes, such as the Chihuahua, are prone to ulceration or irritation of the eye such as ulcerative keratitis; keratitis sicca (dry eye – deficiency of tear production); corneal disease as a result of inadequate blinking (due to large distance between upper an lower lids). These all result from selection for a certain size of dog, shape of head and skull and appearance of the eye. Selection for very small dogs with certain head formation can reduce the space available for the tear duct causing the eyes to run constantly.
Sensory problems are also associated with coat colour. The piebald, extreme white and merle coat colours are associated with deafness, selection against which would eliminate the problem. The high prevalence of deafness in the Dalmatian breed is associated with spotting – a prerequisite of the breed standard. Allowing patches would help to reduce this problem.
Some problems of the central nervous system are associated with conformation. Chiari malformation and Syringomyelia (CMSM) result from selection for a skull which is steep at the back, causing overcrowding of the nervous tissue. CMSM can cause lifelong pain and discomfort for a dog (Cavalier King Charles Spaniel).
Hydrocephalus (increased volume of fluid in the ventricles of the brain) can commonly occur in small and brachycephalic dog breeds. Cranioschisis (where the skull fails to close and affects brain development) is associated with breeds with dome shaped heads.
Cervical disc disease (Wobblers syndrome) is associated with fast growth rates, heavy heads and long necks (in particular Dobermans and Great Danes). Compression of the spinal cord causes neck pain and reduced co-ordination of the hind limbs.
Cervical intervetebral disc disease is associated with fast growing breeds where disc protrusion occurs as a result of fibrous degeneration. This can result in compression of the spinal cord and neck pain.Ref: A Preliminary Investigation into Inherited Defects in Pedigree Dogs (Collins et al, Royal Veterinary College 2009)