Animalia Life

The Breed History
The Yorkie’s origins trace from Scottish terrier lines in the Victorian era, specifically the Waterside terrier crossed with Paisley, Skye, Clydesdale, and rough coated Black and Tan English terriers. This terrier went to Yorkshire England from Scotland as a companion for immigrating weavers. They were brought to the USA in the late 1800s, and AKC recognition occurred in 1885.

Breeding for Function
This terrier was originally used to help control vermin. It was originally much larger, but was progressively bred for smaller body size, and as a companion dog, enjoys travel in purses and totes.

Physical Characteristics
Height at Withers: female 6" (15 cm), male 7" (18 cm)
Weight: females less than 7 lb (3 kg), males less than 7 lb (3 kg). They average 3-5 lb (1.5-2 kg)
Coat: The long silky, low-shed straight haircoat is colored the trademark blue and tan. Coats are parted over the topline and the forehead in the middle, or more commonly, the topknot is tied up. The body coat has a dark blue metallic highlight that develops at maturity. Puppies are born black and tan.
Longevity: 12-15 years.
Points of Conformation: Yorkies possess a small head, the eyes are prominent, large and dark, the nose is black and button shaped, ears are set high, V-shaped and held pricked up or semi-erect. The muzzle is tapering and trim. The tail is generally docked to one half length, and the compact body has a short, level topline. Dewclaws are usually removed, and nail color is black. They move with agility and straight, medium-length strides.

Recognized Behavior Issues and Traits
Reported breed characteristics include: Though very active, they make a suitable city pet. These little dogs are spunky, loyal and intelligent. They are sometimes aggressive to other animals, and may snap if alarmed or frightened. They should be introduced to children and other pets at an early age. They may prefer older quiet children. They will readily alarm bark. They need plenty of attention. They are low shedders that require regular grooming, and are known not to tolerate temperature extremes well. They are considered of moderate trainability.

Normal Physiologic Variations
Cardiac Ventricular and Hemisphere Size: Ratio of cardiac ventricular to hemisphere size measured to 5.3 by low-field MRI.1 Radiographic Vertebral Heart Scale: Heart size was measured on right lateral recumbent thoracic radiographs. There was a trend for dogs with cardiac disease (but not respiratory disease) to have higher mean values on the scale than normal dogs of the same breed. This was most consistent in Yorkshire terriers with dilatative cardiac disease.

Drug Sensitivities
None reported

Inherited Disease Patella Luxation: Polygenically inherited congenital laxity of patellar ligaments, causing medial luxation, lameness, and later degenerative joint disease. OFA reports 23.8% affected. Dorn reports a 7.86x odds ratio versus other breeds. Another study reports a 8.3x odds ratio versus other breeds. Reported at a frequency of 6.2% in the 2006 YTCF Health Survey.
Legg-Calve-Perthes Disease: Polygenically inherited aseptic necrosis of the femoral neck. Can be unilateral or bilateral, with onset of degeneration usually under 9 months of age. Treat surgically if causing lameness or discomfort. Yorkshire terriers have a 35.8x odds ratio for developing the disease versus other breeds. OFA reports 5.0% affected. Reported at a frequency of 7.8% in the 2006 YTCF Health Survey.
Hip Dysplasia: Polygenically inherited trait causing degenerative joint disease and hip arthritis. OFA reports 5.0% affected. Reported at a frequency of 2.2% in the 2006 YTCF Health Survey.
Elbow Dysplasia: Polygenically inherited trait causing elbow arthritis. Too few Yorkshire Terriers have been evaluated by the OFA to determine an accurate frequency in the breed.

Disease Predispositions
Tracheal Collapse: Causes persistent cough, especially when excited. Dorn reports a 36.73x odds ratio for tracheal collapse versus other breeds. Usually occurs in middle-aged to older dogs. Usually poorly responsive to surgery. Many cases can be controlled medically. Reported at a frequency of 17.4% in the 2006 YTCF Health Survey.
Allergic Dermatitis: Inhalant or food allergy presents with pruritis and pyotraumatic dermatitis (hot spots). Reported at a frequency of 16.6% in the 2006 YTCF Health Survey.
Hypoglycemia: Neonatal and young juvenile Yorkshire terriers can develop transient hypoglycemia when stressed. May be related to inadequate gluconeogenesis. Prevented by frequent feeding of a high-energy, protein-rich diet to both mother and pups. Reported at a frequency of 15.8% in the 2006 YTCF Health Survey.
Valvular Heart Disease (Chronic Myxomatous Valvular Endocardiosis): Degenerative valvular thickening and regurgitation affecting primarily the mitral valve; though the tricuspid valve (34% of cases) and aortic valve (3% of cases) can also be involved. Secondary dilation of the left atrium and left ventricle develop, leading to congestive heart disease. Considered an age related change in small breeds, however seen in increased frequency at a younger age in this breed. Reported at a frequency of 12.6% in the 2006 YTCF Health Survey.
Portosystemic Shunt (PSS, Liver Shunt): Congenital abnormal blood vessel connecting the portal and systemic circulation. Can be intrahepatic or extrahepatic. Hepatic Microvascular Dysplasia may also be genetically related to this condition. Causes stunting, abnormal behavior, possible seizures, and secondary ammonium urate urinary calculi in the breed (see below). Diagnose with paired fasted and feeding serum bile acid and/or ammonium levels, and abdominal ultrasound. Treatment of PSS includes partial ligation and/or medical and dietary control of symptoms. Studies show a 35.9x to 293x increased incidence in the breed over other breeds. Breeding studies rule out a simple (autosomal dominant, recessive, or x-linked) mode of inheritance. Reported in 3.2% of Yorkshire Terriers presented to veterinary teaching hospitals. PSS is reported at a frequency of 10.4%, and MVD at 3.2% in the 2006 YTCF Health Survey.
Persistent Pupillary Membranes: Strands of fetal remnant connecting; iris to iris, cornea, lens, or involving sheets of tissue. The later three forms can impair vision, and dogs affected with these forms should not be bred. Identified in 9.86% of Yorkshire terriers CERF-examined by veterinary ophthalmologists between 2000-2005.
Keratoconjunctivitis Sicca (KCS, Dry Eye): Ocular condition causing lack of tear production and secondary conjunctivitis, corneal ulcerations, and vision problems. Can be due to Unilateral or Bilateral Aplasia or Hypoplasia of the Lacrimal Gland (Congenital Alacrima) in the breed. KCS is reported at a frequency of 9.6% in the 2006 YTCF Health Survey. CERF does not recommend breeding any Yorkshire Terrier with KCS.
Cryptorchidism (Retained Testicles): Can be unilateral or bilateral. Reported at a frequency of 8.0% in the 2006 YTCF Health Survey.6 Cataracts: Anterior cortex punctate and posterior cortex intermediate cataracts predominate in the breed. Primarily late onset with a mean age of 9.5 years. Identified in 7.08% of Yorkshire terriers CERF examined by veterinary ophthalmologists between 2000-2005. Unknown mode of inheritance. CERF does not recommend breeding any Yorkshire Terrier with a cataract.
Hyperadrenocorticism (Cushing’s Disease): Caused by a functional adrenal or pituitary tumor. Clinical signs may include increased thirst and urination, symmetrical truncal alopecia, and abdominal distention. Treat medically. Reported at a frequency of 5.4% in the 2006 YTCF Health Survey.
Urinary Tract Calculi: Increased incidence of oxalate and ammonium urate bladder stones reported at a frequency of 7.4% in a UK study. Prevalence of ammonium urate stones is secondary to portosystemic liver shunts. Dorn reports a 2.21x incidence in the breed versus other breeds. Yorkshire terriers also have an increased propensity to develop kidney stones.
Progressive Retinal Atrophy (PRA): Presumed autosomal recessive inherited retinal degeneration resulting in blindness. Identified in 3.76% of Yorkshire Terriers CERF examined by veterinary ophthalmologists between 2000-2005. CERF does not recommend breeding any Yorkshire Terrier with PRA. Reported at a frequency of 2.2% in the 2006 YTCF Health Survey.
Distichiasis: Abnormally placed eyelashes that irritate the cornea and conjunctiva. Can cause secondary corneal ulceration. Identified in 2.82% of Yorkshire Terriers CERF-examined by veterinary ophthalmologists between 2000-2005.
Hypothyroidism: Inherited autoimmune thyroiditis. 2.5% positive for thyroid autoantibodies based on testing at Michigan State University. (Ave. for all breeds is 7.5%).
Diabetes Mellitus: Sugar diabetes. Associated with mutations in the CTLA4 promoter gene. Treat with insulin injections, diet, and glucose monitoring. Increased incidence seen in the breed. Dorn reports a 3.45x increased odds ratio versus other breeds. Reported at a frequency of 2.4% in the 2006 YTCF Health Survey.
Corneal Dystrophy: Either the epithelial/stromal, or endothelial form of corneal dystrophy can be seen in the breed. Identified in 1.88% of Yorkshire Terriers CERF examined by veterinary ophthalmologists between 2000-2005.
Protein Losing Enteropathy (PLE, Lymphangiectasia): Presents with diarrhea, weight loss, and/or abdominal effusion due to dilation of lymph vessels in the intestine. Inflammatory cell buildup blocks normal absorption of nutrients. Can occur at any age, but primarily affects middle-aged dogs. Yorkshire terriers are predisposed to this condition. Treatment consists of chronic anti-inflammatory medication and dietary restriction. Some dogs with severe cases have a poor prognosis.
Retinal Dysplasia: Multifocal and geographic retinal dysplasia has been described in families of Yorkshire terriers. Can lead to retinal hemorrhage, retinal detachment, and blindness. Can also be related to subendothelial corneal opacities. Diagnosis by ophthalmoscopic examination. Identified in 0.94% of Yorkshire terriers CERF examined by veterinary ophthalmologists between 2000-2005. Unknown mode of inheritance.
Necrotizing Meningoencephalitis: Rare disorder causing sterile, multifocal/diffuse encephalitis. Associated with a DLA haplotype. Can cause seizures, or focal neurological signs depending on the location of brain lesions. Age of onset 2-10 years of age. Diagnosis by CSF tap and MRI or CT, or post-mortem. No treatment is available.
Cutaneous Plasmacytoma: Eight of 63 dogs diagnosed with cutaneous or mucocutaneous plasmacytoma were Yorkshire terriers. Prognosis was good with removal.
Dermatophytosis (M. Canis): Ringworm. Increased incidence found in the breed. In one study, it was possibly secondary to immunosuppression from infection with leishmaniasis, ehrlichiosis, or with diabetes mellitus.

Isolated Case Studies
Epitheliotropic Cutaneous (T-Cell) Lymphoma (Mycosis Fungoides): Case report of a 7 year old male Yorkshire Terrier with chronic skin and oral lesions.
Renal Cortical Hypoplasia: Case report of a young Yorkshire terrier with congenital malformation of the kidneys causing juvenile renal disease and kidney failure.
Dermoid Sinus and Spinal Malformations: Case report on one young Yorkshire terrier.
Hypertrophic Cardiomyopathy (HCM): One case report of a 14 year old Yorkshire terrier with a cardiac murmur and syncope due to outflow obstruction, and one case report of occult HCM in a 6 year old female Yorkshire Terrier that died under anesthesia.
Persistent Right Aortic Arch: A 5-year-old neutered male Yorkshire terrier first presented with regurgitation at 3 months of age, and was maintained on a modified diet and motility enhancing drugs. Megaesophagus was diagnosed at 2 years of age, and vascular ring anomaly was diagnosed at 4 years of age. Surgery was performed at 5 years of age.
Lung Lobe Torsion: Case report of a 9 year old female Yorkshire Terrier with lung lobe torsion. Treatment was surgical removal.
Color Dilution Alopecia, Hypotrichosis, Patent Ductus Arteriosus, Retained Primary Teeth, Shaker Syndrome, and von Willebrand’s Disease are reported.

Genetic Tests
Tests of Genotype: None
Tests of Phenotype: CHIC Certification: CERF eye examination (at 1, 3, and 6 years) and patella evaluation. Optional tests include hip radiograph (for Legg-Perthes or hip dysplasia), thyroid profile including autoantibodies (at 1, 3, and 6 years), blood donation to the Cornell DNA bank, or to the CHIC DNA repository. (See CHIC website; caninehealthinfo.org).
Recommend paired fasted and feeding serum bile acid and/ or ammonium levels for PSS, cardiac examination and elbow radiographs.

Miscellaneous
• Breed name synonyms: Yorkie, Broken-haired Scotch terrier (historical)
• Registries: CKC, AKC, UKC, KCGB (Kennel Club of Great Britain), ANKC (Australian National Kennel Club), NKC (National Kennel Club)
• AKC rank (year 2008): 2 (41,914 dogs registered).
• Internet resources: Yorkshire Terrier Club of America: ytca.org
Yorkshire Terrier Club Foundation: yorkiefoundation.org
The Yorkshire Terrier Club (UK): the-yorkshire-terrier-club.co.uk
The Canadian Yorkshire Terrier Association: cyta.ca