The Jack Russell is a small terrier type dog with origins in Hunting. In the early 19th century, they were originated from dogs that were bred and used by Reverend John Russell (from whom the breed takes its name), and can trace their origin to the now extinct English White Terrier. The dog was bred to be mostly white dog in hopes that it would make differentiating the dog from the creature it was hunting easier. A small white and tan female terrier named Trump was used by Russell as the basis for a breeding program to develop a terrier with high stamina, as well as the courage and formation to chase out grounded foxes.
This is a sturdy, tough, and tenacious breed and weigh in at 14-18 pounds. They will measure between 10-15 inches tall at the withers. The head of the Jack Russell is of moderate width at the ears and will narrow towards the eyes. It will be slightly flat between the ears. The stop should be defined but not over pronounced at the end of the muzzle where it meets the head. The eyes are dark colored and almond shaped. They should be full of life and intelligence. He has small V-shaped ears that are of moderate thickness. They are carried forward on the head. The tail is set high and docked to approximately 5 inches. They may sport a smooth, rough, or broken coat. All coat types should have dense double coats that are neither silky nor woolly. They are predominantly white and have black or tan markings.
Because of the breeds working ability, these dogs tend to be extremely intelligent, fearless, athletic, and vocal dogs. If not properly stimulated and exercised, they may become moody or destructive, as they have a tendency to bore easily. If not properly socialized the Jack Russell can be stubborn at times and aggressive towards other animals and humans. While they are friendly towards children if properly socialized, they will not tolerate abuse even if it is unintentional. They have a large amount of energy for their small size, which sometimes leads to trouble involving larger animals.
The average lifespan of the breed is from 13-16 years. Some health issues found within the breed include hereditary cataracts, ectopia lentis, congenital deafness, patellar luxation, ataxia, myasthenia gravis, Legg–Calvé–Perthes syndrome and von Willebrand disease.