Berners are outdoor dogs at heart, though well-behaved in the house; they need activity and exercise, but do not have a great deal of endurance. They can move with amazing bursts of speed for their size when motivated.

The Berner temperament is a strong point of the breed. Affectionate, loyal, faithful, stable and intelligent, Bernese Mountain Dogs make wonderful family pets. They are very trainable provided the owner is patient and consistent in training; Berners need time to think things through. The breed is stable in temperament, and is patient and loving.

This dog breed genetic base is somewhat narrow, so hereditary diseases and inbreeding depression are major issues. Several kinds of cancer (malignant histiocytosis, mastocytoma, lymphosarcoma, fibrosarcoma, osteosarcoma) commonly affect Berners; hip dysplasia, elbow dysplasia, osteoarthritis, aortic stenosis plus autoimmune and kidney problems are other major health issues for the breed. Many litters contain stillborn young, a major indicator of inbreeding depression.

Although slow to mature, the Berner is not particularly long-lived. The Swiss say, “three years a young dog, three years a good dog, and three years an old dog.� Today even nine years may be slightly optimistic; certainly a ten-year-old Berner is a very old one. In fact, surveys around the world show that the average lifespan is seven years, primarily as a result of the prevalent occurrence of cancers.

source; wikipedia.org