They typically weigh from 15 to 20 lbs for male dogs and 13 to 16 lbs for female dogs and their average height is 9 to 11 inches (28 cm) at the withers. The Kennel Club has recommended that their tails, typically "carrot-shaped", should never be docked.> The tail should be between 5-6 inches.
They also have deep chests, muscular limbs, a huge skull, a short and a closely fitted jaw with "scissors" bite (lower canines locked in front of upper canines, upper incisors locked over lower incisors). Their teeth generally appear quite large for the size of the dog. Westies have a very strong bone structure for their size.
They have a soft, dense undercoat and a rough outer coat, about 2 inches long, that requires regular grooming. Some Westies have "wheaten tippings" on their backs, though for individuals put forward for conformation showing this can be regarded as undesirable.
Their paws are slightly webbed and thickly padded.
West Highland White Terrier puppies may be affected by a disease known as craniomandibular osteopathy, known colloquially as "Lion Jaw". The disease has a genetic component: it is an autosomal recessive condition i.e. for a puppy to be affected by the disease, both the parents must be carriers of the faulty gene. With this disease, the only current way to identify carrier breeding stock is if an affected puppy is produced. Therefore, breeders may be unaware that breeding stock are carriers until an affected puppy is born.
Craniomandibular osteopathy is a non-neoplastic proliferative disease of the ventral mandibular ramus, occipital base of the skull and tympanic bullae, characterised by excessive bone deposition in these areas. In most incidences, the defect is bilateral, although this is not always the case. The disease varies in severity, the region(s) affected and the individual pain threshold of the affected puppy. Definitive diagnosis is achieved by radiographic examination.
Craniomandibular osteopathy is extremely painful to the puppy: affected puppies will most likely display signs of pain or discomfort, such as yelping, when their head is touched and when chewing or eating. The puppy may be lethargic and be reluctant to eat as a result. The condition usually manifests when the puppy is c. 3-6 months of age, and regresses spontaneously by c. 12 months of age. Treatment of the disease is concerned with managing the symptoms and providing appropriate analgesia to improve quality of life and enable the puppy to eat until the disease resolves spontaneously. Corticosteroids are the usual therapeutic agents used to manage the disease. The exact treatment protocol depends on the severity, localisation and pain sensitivity of the affected puppy. In extreme cases, euthanasia may be required.
Westies are descended from Cairn Terriers, who occasionally whelped white puppies naturally, and Scottish Terriers; who also occasionally produced white offspring. White offspring from other terriers such as the Bedlington Terrier and Dandie Dinmont Terrier were occasionally introduced to the bloodline for desired characteristics, but this practice generally stopped in the 1850s.
Some sources also credit Colonel Edward Donald Malcolm and his kin of Poltalloch, in the Argyll region of western Scotland as an originator of this breed in the 1800s. Other sources credit the 8th Duke of Argyll (Chieftain of Clan Campbell) as an originator of the breed. However, there may have been some cooperation between the two gentlemen. It may have taken as long as a hundred years of selective breeding to produce all the desired qualities. Their white coat made them highly visible when hunting on the Scottish moors and easily distinguished them from their game (this was an extremely important factor because hunters sometimes mistook brown dogs for foxes, and shot them). They also possess a sturdy frame.
Originally the breed was known as the Poltalloch Terrier (after the name of Malcolm's home); they were also known as the Roseneath Terrier (after the name of Argyll's home; see Rosneath), White Roseneath Terrier, and at the end of the 19th century, briefly as a white variety of the Scottish Terrier.
Westies are bred for hunting. Their prey is usually small animals such as rabbits, squirrels and mice, but they were also used to hunt foxes and badgers. Young females are known as the keenest hunters. Ideally, a prospective owner should buy two males for company, as males often get lonely.