They are competent swimmers unlike most other bulldog breeds, though they do not have the affinity for water a retriever would: they swim if they have to do it, not because they particularly enjoy it.They are capable of jumping in excess of 3 feet (0.91 m) vertically due to the dense muscle build of the breed and they love to run, jump, tackle and cavort. Some health problems in American bulldogs are often found within certain genetic lines, and are not common to the entire breed, while others, such as neuronal ceroid lipofuscinosis (NCL), Ichthyosis, disorders of the kidney and thyroid, ACL tears, hip dysplasia, cherry eye, elbow dysplasia, entropion, ectropion, and bone cancer are more common to the general population of American Bulldogs. There are DNA tests available to help breeders screen breeding animals for NCL (neuronal ceroid lipofuscinosis) and Ichthyosis.