The Jack Russell Terrier is a small terrier that has its origins in fox hunting. It is principally white-bodied and smooth, rough or broken-coated.

The Jack Russell is frequently confused with the Parson Russell terrier (see the American Kennel Club) and the Russell terrier, which is a shorter-legged, stockier variety. (Within the Fédération Cynologique Internationale, the "Russell terrier" is also known as "Jack Russell terrier".) The term "Jack Russell" is also commonly misapplied to other small white terriers. The Jack Russell is a broad type, with a size range of 10–15 inches (25–38 cm). The Parson Russell is limited only to a middle range with a standard size of 12–14 inches (30–36 cm), while the Russell terrier is smaller at 10–12 inches (25–30 cm). Each breed has different physical proportions according to the standards of their breed clubs.

Jack Russells are an energetic breed that rely on a high level of exercise and stimulation, and are relatively free from serious health complaints. Originating from dogs bred and used by Reverend John Russell in the early 19th century, from whom the breed takes its name, the Jack Russell has similar origins to the modern Fox terrier. It has gone through several changes over the years, corresponding to different use and breed standards set by kennel clubs. Recognition by kennel clubs for the Jack Russell breed has been opposed by the breed's parent societies – which resulted in the breeding and recognition of the Parson Russell terrier. Jack Russells have appeared many times in film, television and print - with several historical dogs of note.

TEMPERAMENT

Jack Russells are first and foremost a working terrier.Originally bred to bolt fox from their dens during hunts, they are used on numerous ground-dwelling quarry such as groundhog, badger, and red and grey fox. The working JRT is required to locate quarry in the earth, and then either bolt it or hold it in place until they are dug to. To accomplish this, the dog will not bark but will expect attention to the quarry continuously. Because the preservation of this working ability is of highest importance to most registered JRTCA/JRTCGB breeders, Jack Russells tend to be extremely intelligent, athletic, fearless, and vocal dogs. It is not uncommon for these dogs to become moody or destructive if not properly stimulated and exercised, as they have a tendency to bore easily and will often create their own fun when left alone to entertain themselves.

Their high energy and drive make these dogs ideally suited to a number of different dog sports such as flyball or agility.Obedience classes are also recommended to potential owners, as Jack Russells can be stubborn at times and aggressive towards other animals and humans if not properly socialized. Despite their small size, these dogs are not recommended for the condominium or apartment dweller unless the owner is ready to take on the daunting task of providing the dog with the necessary amount of exercise and stimulation. They have a tremendous amount of energy for their size, a fact which can sometimes lead to trouble involving larger animals.They may seem never to tire and will still be energetic after their owner has called it a day. While socialised members of the breed are friendly towards children, they will not tolerate abuse even if it is unintentional.

 

Health

Thee breed has a reputation for being healthy with a long lifespan. Breeders have protected the gene pool, and direct in-line breeding has been prevented. Jack Russells can live from 13 to 16 years given proper care. However certain lines have been noted for having specific health concerns, and therefore could occur in any line or generation because of recessive genes. These issues can include hereditary cataracts, ectopia lentis, congenital deafness, patellar luxation, ataxia, myasthenia gravis, Legg–Calvé–Perthes syndrome and von Willebrand disease.Being a hunt-driven dog, the Jack Russell will usually pursue most creatures that it encounters. This includes the skunk, and the breed is prone to skunk toxic shock syndrome. The chemical in the skunk spray is absorbed by the dog and causes the red blood cells to undergo haemolysis, which can occasionally lead to fatal anaemia and kidney failure. If sprayed underground, it can also cause chemical burning of the cornea. Treatments are available to flush the toxin out of the dog's system.

Eye disorders

Lens luxation, also known as ectopia lentis is the most common hereditary disorder in Jack Russell terriers. Even so, this condition is not a common occurrence in the breed. Most frequently appearing in dogs between the ages of 3 and 8 years old, it is where the lens in one or both eyes becomes displaced. There are two types, posterior luxation (where the lens slips to the back of the eye) and anterior luxation (where the lens slips forward). Posterior luxation is the less severe of the two types, as the eye can appear normal although the dog's eyesight will be affected. In anterior luxation, the lens can slip forward and rub against the cornea, damaging it. Anterior luxation also has a high probability of causing glaucoma which can lead to partial or complete blindness. Treatment is available and may include both medical and surgical options. Secondary lens luxation is caused by trauma to the eye, and is not hereditary.The condition appears in a number of terrier breeds as well as the Border collie, Brittany and Cardigan Welsh corgi.

Cataracts can affect any breed of dog, and is the same condition as seen in humans. Here the lens of the eye hardens and is characterised by cloudiness in the eye.Cataracts will blur the dog's vision and can lead to permanent blindness if left untreated. While considered mainly a hereditary disease, it can also be caused by diabetes, old age, radiation, eye injury or exposure to high temperatures.

Musculoskeletal conditions

Patellar luxation, also known as luxating patella, is a hereditary disorder affecting the knees. It is where the kneecap slips off the groove on which it normally sits. The effects can be temporary with the dog running while holding its hind leg in the air before running on it again once the kneecap slipped back into place as if nothing has happened. Dogs can have a problem with both rear knees, and complications can include arthritis or torn knee ligaments. Severe cases can require surgery. Some are prone to dislocation of the kneecaps, inherited eye diseases, deafness and Legg Perthes—a disease of the hip joints of small dog breeds. Prone to mast cell tumors. Legg–Calvé–Perthes syndrome, also called Avascular Necrosis of the Femoral Head, is where the ball section of the femur in the hip joint deteriorates following interruption of the blood flow and is the same condition as in humans. In dogs, this causes lameness of the hind-legs, the thigh muscles to atrophy and pain in the joint. It usually occurs between 6–12 months of age and has been documented in a variety of other terrier breeds including the Border terrier, Lakeland terrier and Wheaten terrier.