Animalia Life

The Breed History
The breed was cultivated for over 200 years in the south of England. The breed progenitors are thought to be the extinct Black-and-Tan terrier and the Old English White Terrier. The first Jack Russell terrier dogs were brought to America around 1930. Breed nomenclature is quite confusing. Parson Jack Russell Terrier was often used as a synonym for this breed, but in England and in the UKC standard, the Parson Jack Russell Terrier breed is different. Differences in the Parson terrier standard include inclusion of three coat types, longer legs and shorter body, and being larger in stature. In those constituencies, the Jack Russell Terrier breed name is limited to terriers standing less than twelve inches. Parson John Russell was considered to be the original breeder of this general type of terriers. The Jack Russell terrier breed is popular with the horsy set, and further gained popularity following feature roles in television series as the Eddie and Wishbone characters.

Breeding for Function
Fox hunting and ratting was the original purpose for which the breed determination, fearlessness and agility were bred into them. They were baying terriers, and were not developed to kill the quarry, just bolt them out.

Physical Characteristics
Height at Withers: AKC ideal size is for the male, 14" (35.5 cm), and female 13" (33 cm)
Weight: 9 lb (4 kg) up to 13-17 lb (6-7.5 kg)
Coat: Two coat types in the AKC standard:
Smooth: Double coated with a hard outer flat layer and a dense undercoat.
Broken: Also double coated, but the outer coat stands flat and is broken, with some curling and waving of the hairs.
White or predominantly white with tan or black, and also tri-color are accepted colors. Brindle is disqualifying but grizzled is acceptable. Markings are preferred on extremities such as the face, ears and tail tip.
Longevity: 13-15 years
Points of Conformation: Jack Russell Terriers are medium-boned and well muscled with almost square conformation. They possess a keen expression and lively attitude. The eyes are moderate in size, dark in color and almond-shaped. They have small triangular ears with moderately thick leathers, pointed tips, and ears are folded forward with the fold at the level of the top of the skull or slightly higher. The head is also characterized by a flat skull, well-defined stop and black nose. The moderately long and arched neck is free of throatiness. The topline is level, abdomen is moderately tucked up, and the thorax is moderate in depth and narrow. The tail is high set and thick and normally docked to provide a handhold length at maturity (4" or 10 cm), Limbs are straight boned, feet are compact with tough pads, and the gait is powerful with long strides.

Recognized Behavior Issues and Traits
Reported breed attributes include: High activity, sometmes hyperactive in fact, happy, but can be snappy or aggressive with moving targets and other dogs. May see small pets as prey even after being socialized to them. Also described as intelligent, bouncy, springy, lively (exuberant), friendly with family and strangers, though some are aloof with strangers. They have low grooming needs. Considered good in town or country but not for condo or apartment life. They have a moderate shedding tendency. They are diggers, and have high exercise needs. Fences need to be high and secure since they can climb over and dig under fences quite effectively. They like close human companionship, and activities that provide mental stimulation to help prevent boredom vices. They have a high barking tendency, and are good alarm barkers. Their assertive nature means that early socialization to children and other pets, and obedience training are important. Not recommended for homes with children under 6 years of age since they do not always tolerate young children well.

Normal Physiologic Variations
None reported

Drug Sensitivities
None reported

Inherited Diseases
Primary Lens Luxation (PLL) and Secondary Glaucoma: An autosomal recessive gene causes partial or complete displacement of the lens from its normal anatomic site behind the pupil. Relative risk of 9.03x versus other breeds. Parson Russell terriers have a 7.1x odds ratio for secondary glaucoma with blindness due to lens luxation versus other breeds. Homozygous affected dogs usually develop lens luxation between 4-8 years of age. Rarely, heterozygous carriers can develop lens luxation, but at a later age. A genetic mutation has been identified, and a genetic test is available. OFA testing shows 23% carrier, and 1% affected for Parson Russell Terriers, and 36% carrier and 3% affected for Jack Russell Terriers.
Deafness: Polygenically inherited congenital deafness can be unilateral or bilateral. Diagnosed by BAER testing. Strain reports 16.1% testing unilaterally or bilaterally deaf based on BAER testing. Heritability is between 0.22-0.31. There is a pigmentation association with deafness in this breed, as mostly white dogs are more likely to be deaf.
Hip Dysplasia and Legg-Calve Perthes Disease: Polygenically inherited traits causing degenerative hip joint disease and arthritis. OFA reports 4.0% affected with hip dysplasia, and 3.0% affected with Legg-Calve-Perthes disease.
Elbow Dysplasia: Polygenically inherited trait causing elbow arthritis. OFA reports 2.7% affected.
Cataracts: Polygenically inherited in this breed. Posterior cortex intermediate cataracts predominate in the breed. Heritability estimate of 0.73. Identified in 3.78% of Parson Russell terriers CERF-examined by veterinary ophthalmologists between 2000-2005. CERF does not recommend breeding any Parson Russell Terrier with a cataract.
Patella Luxation: Polygenically inherited laxity of patellar ligaments, causing luxation, lameness, and later degenerative joint disease. Treat surgically if causing clinical signs. OFA reports 0.8% affected.
Hereditary Ataxia (Axonopathy, Neuroaxonal Dystrophy): An inherited axonopathy in the breed produces a gait disturbance between 2-9 months of age with symmetric generalized ataxia and hypermetric and spastic movements. Seizures and respiratory distress can also occur. Pathological lesions occur throughout the central nervous system. The disorder appears to have a polygenic mode of inheritance.
Hyperuricosuria (HUU)/Urate Bladder Stones: An autosomal recessive mutation in the SLC2A9 gene causes urate urolithiasis and can predispose male dogs to urinary obstruction. Estimated at a carrier frequency of 7.75% in the breed. A genetic test is available.
Myasthenia Gravis: An autosomal recessive, congenital form of myasthenia gravis occurs in Parson Russell terriers. Clinical signs are evident from six to eight weeks of age, and include exercise induced weakness without megaesophagus. Raised antibody levels to acetylcholine receptor do not occur, although the amount of receptor in the end-plates is decreased.
Severe Combined Immunodeficiency (SCID): Autosomal recessive disorder, where affected dogs cannot generate antigen-specific immune responses. Parson Russell terrier puppies with SCID succumb to infections at a few months of age. A commercial genetic test is not available.
Nonepidermolytic Ichthyosis: A rare, autosomal recessive disease in Jack Russell Terriers presenting with congenital, non-alopecic or pruritic, thick, adherent, scales. As adults, the scales persist and secondary infections with coccoid bacteria and yeasts are common. Pathology reveals orthokeratotic hyperkeratosis that extends into follicular infundibula. The disease is caused by an insertion of a LINE-1 into the TGM1 gene. A genetic test is not available.

Disease Predispositions
Hypothyroidism: 4.1% positive for thyroid auto-antibodies based on testing at Michigan State University. (Ave. for all breeds is 7.5%).
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 3.47% of Parson Russell terriers CERF-examined by veterinary ophthalmologists between 2000-2005.
Secondary Glaucoma: Increased intraocular pressure can cause retinal deterioration and blindness. Can occur after cataract formation, lens luxation, or uveitis. Screen with tonometry. One report found an odds ratio of 7.1x for secondary glaucoma in Jack Russell Terriers.
Autoimmune Hemolytic Anemia (AIHA): Auto-immune destruction of red blood cells. Parson Russell terriers have a 2.8x risk of developing AIHA versus other breeds. Females are more frequently affected than males. Clinical features included pale mucous membranes, weakness, lethargy and collapse. Treatment with prednisone is successful in most cases.
Distichiasis: Abnormally placed eyelashes that irritate the cornea and conjunctiva. Can cause secondary corneal ulceration. Identified in 2.42% of Parson Russell terriers CERF-examined by veterinary ophthalmologists between 2000-2005.
Primary (Narrow Angle) Glaucoma: Ocular condition causing increased pressure within the eyeball, and secondary blindness due to damage to the retina. Diagnose with tonometry and gonioscopy. Diagnosed in 1.37% of Parson Russell Terriers presented to veterinary teaching hospitals.
Pulmonic Stenosis: Clinical signs can include exercise intolerance, stunting, dyspnea, syncope and ascites, leading to heart failure. Diagnosis by auscultation for a heart murmer, and echocardiography. Parson Russell Terriers are overrepresented versus other breeds.
Portosystemic Shunt (PSS, Liver Shunt): Abnormal blood vessels connecting the systemic and portal blood flow. Vessels can be intrahepatic or extrahepatic. Causes stunting, abnormal behavior, possible seizures, and secondary ammonium urate urinary calculi. Diagnose with paired fasting and post-feeding bile acids and blood ammonia, and abdominal ultrasound. Tobias reports a 8.5x odds ratio versus other breeds. Undetermined mode of inheritance.
Malassezia Pachydermatis infection: Yeast skin infection. Affected dogs present with pruritus, alopecia and lichenification. Parson Russell terriers are significantly overrepresented versus other breeds. Can also be secondary to ichthiosis in the breed.
Episodic Myokymia and Neuromyotonia: Jack Russell Terriers affected with Hereditary Ataxia can develop episodes of generalized muscle stiffness and delayed muscle relaxation resulting in collapse into lateral recumbency. Episodes can be preceded by intense facial rubbing, and can be associated with severe hyperthermia. An underlying neuronal ion channel dysfunction is suspected.
Black Hair Follicular Dysplasia, Brachygnathism, Compulsive Tail Chasing, Epilepsy, Oligodontia, Prognathism, and Progressive Retinal Atrophy, are reported.
Isolated Case Studies
Sry-Negative XX Sex Reversal (Hermaphrodism): Identified in a Parson Russell terrier. An autosomal recessive disorder, where outwardly male dogs are chromosomal females (XX), and there is an absence of male causing SRY.
Colonic Duplication: Identified in a 4-month-old male Parson Russell terrier because of stranguria and tenesmus.
Factor X Deficiency: Deficiency in Factor X (Stuart-Prower factor) was identified in a 7-month-old spayed female Parson Russell terrier following recurrent bleeding episodes. Low Factor X was also identified in the father and paternal grandmother. Factor X deficiency may be an autosomal dominant trait with variable expression.
Mitochondrial Myopathy: A stunted, thin four month old Parson Russell terrier with a stilted gait and progressive exercise intolerance was examined. The dog had raised lactate levels before and after feeding and a raised lactate/pyruvate ratio after feeding, indicating a metabolic abnormality. Ultrastructural examination of the muscle confirmed the presence of subsarcolemmal accumulations of mitochondria.
Mitochondrial Encephalomyopathy: A 10-month-old female Parson Jack Russell terrier was euthanized because of therapy-resistant ataxia, hypermetria, and deafness that had first been observed at 10 weeks of age. Pathological findings included severe, bilateral, symmetrical neuronal degeneration and mineralization of the brain, and hepatocytes and cardiac myocytes with increased numbers of enlarged or misshapen mitochondria.
Acute Necrotising Pulmonary Vasculitis: Identified in a 5 month-old female Jack Russell terrier with acute lethargy, coughing, and respiratory distress. Tests revealed severe pulmonary hypertension, cor pulmonale and right-sided heart failure. Pathology revealed acute necrotising pulmonary arteritis without any cardiac abnormalities or immune complex disease.
Myotonia Congenita: A 4-month-old male Jack Russell terrier was evaluated for non-painful muscle spasms and exercise induced hindquarter bunny-hopping and collapse. He had non-painful hypertrophic muscles, and was found to have a mutation in the chloride ion channel gene for MC.

Genetic Tests
Tests of Genotype: Direct test for lens luxation is available from OFA and AHT. Direct test for HUU is available from the UC-Davis VGL and the Animal Health Trust.
Tests of Phenotype: CHIC Certification: Required testing includes CERF eye examination, patella examination, and BAER test for deafness. Recommended tests include hip and elbow radiographs, thyroid profile including autoantibodies, and cardiac examination.

Miscellaneous
- Breed name synonyms: Jack Russell, JRT, Jack, Parson Jack Russell Terrier, English Jack Russell Terrier
- Registries: AKC, UKC (Parson Russell Terrier), KCGB (Kennel Club of Great Britain) (also as Jack Parson Russell Terrier), ANKC (Australian National Kennel Club), NKC (National Kennel Club)
- AKC rank (year 2008): 84 (802 dogs registered)
- Internet resources: Parson Russell Terrier Association of America: www.prtaa.org
The Parson Russell Terrier Club (UK): www.parsonrussellterrierclub.co.uk
Association of Parson Russell Terrier Fanciers (Canada): http://aprtf.webs.com
English Jack Russell Terrier Club Alliance Inc.: www.ejrtca.com (under 12" height dog registry)
Jack Russell Terrier Club of America: www.therealjackrussell.com
Jack Russell Terrier Club of Canada: www.jrtca.com