These can be corrected with a relatively minor surgical procedure. This condition is considered a major fault, however, and dogs known to carry the gene are not allowed to breed. Bone cancer is a frequent cause of death in giant breeds, and Leonbergers are no exception. However, it usually does not strike until dogs have passed their seventh year and frequently much later. Osteosarcoma is a a highly destructive tumor state which spreads rapidly to other organs, particularly the lungs.
Treatment often requires amputation of the affected limb combined with chemotherapy.
Also known as gastric dilation, bloat can occur in any breed. In deep-chested breeds, like the Leonberger, the stomach can fill with gas and twist trapping the gas inside. This is a life-threatening event which must be treated immediately. As a preventative measure, Leos should be fed from raised bowls and should not be vigorously exercised or stressed for at least one hour after feeding.