A new 20-year retrospective study from the University of Georgia examined causes of death in dogs between 1984 and 2004. Researchers looked at records of 74,566 dogs from the Veterinary Medical Database, which includes data from 27 veterinary teaching hospitals. These results may be biased toward more severe, complicated, or unusual causes than the general dog population, but are fascinating nonetheless.
The study grouped deaths by organ system and by disease category (“pathophysiological process”), and analyzed results based on age, breed, and average breed size. Eighty-two breeds with at least 100 representatives were included in breed-based analyses; mixed-breed dogs were considered as one group.
Only conditions that led to death were considered; if a dog had multiple conditions, only one was deemed the cause of death.
The study found that cancer was by far the most common disease category cause of death in adult dogs; cancer was the leading cause of death in all but 11 breeds! Almost a third of all adult dogs were found to have died of cancer. Cancer was designated the cause of death almost three times as often as the next most common category of deaths (trauma).
Interestingly, the frequency of cancer deaths begins to taper after age 10.
Cancer occurred less frequently in small breeds, with the exception of the Boston Terrier and Cairn Terrier (30 and 32 percent respectively of deaths in those breeds were from cancer).
The Miniature Pinscher had the lowest rate of cancer at 3.6 percent. Other breeds with low percentages of death from cancer include Miniature Dachshund (6.0), Chihuahua (7.5), Pekingese (7.9), Pomeranian (7.9), Dachshund (8.9), and Maltese (9.2).
The most common causes of death for puppies (dogs less than one year of age) by disease category are very different than for adult dogs. Puppies were overwhelmingly most likely to die of infection, trauma, or congenital disease. About 60 percent of all puppies died from something in these three disease categories.
When looking at deaths classified by organ system, the gastrointestinal and musculoskeletal systems were most commonly involved in the deaths of puppies.
In adult dogs, no single organ system was responsible for a dramatic majority of deaths; seven different organ systems had similar results, ranging from about 8 to 12 percent of adult dog deaths. The leaders (if we can call them that) were the nervous system (neurologic), musculoskeletal, and gastrointestinal systems, followed by the urogenital, hematopoietic, cardiovascular, and respiratory systems.
Older dogs are increasingly likely to die from something involving the cardiovascular system, as well as endocrine, neurologic, and urogenital systems. The frequency of gastrointestinal-related deaths remained fairly constant throughout adulthood, while hematopoietic and musculoskeletal deaths declined with age.
Small-breed dogs were more likely to die from neurologic, endocrine, and urogenital causes. The larger the dog, the more likely they were to die of musculoskeletal and gastrointestinal causes.
Some of the breed differences found were surprising. A higher incidence of cancer in Bernese Mountain Dogs, Golden Retrievers, Scottish Terriers, and Boxers is well-known, but the 47 percent death rate from cancer among Bouvier de Flandres was unexpected.
Cardiovascular disease is well known in toy breeds, such as Chihuahuas and Maltese, because of their high incidence of mitral valve disease, but researchers were surprised to find that the rate was almost as high in Fox Terriers. It’s unknown if that’s because Fox Terriers are more prone to heart disease than previously realized, or if they’re simply more protected from other diseases.
A high proportion of deaths from respiratory disease was expected in Bulldogs due to their brachycephalic airways, but finding that respiratory disease accounted for the highest percentage of deaths in the Afghan Hound and Vizla was unexpected.
Examples of Organ System Problems
The study did not provide details about which diseases are included in each category (my mind boggles at the details left out of published studies), but following are some examples of conditions that are likely to be classifed in each organ system:
–Gastrointestinal – Gastric dilatation and volvulus (GDV, or bloat) is likely the most common gastrointestinal cause of death; other causes would include pancreatitis, inflammatory bowel disease (IBD), intestinal obstruction, perianal fistula, exocrine pancreatic insufficiency (EPI), lymphangiectasia and other forms of protein-losing enteropathy, and cancer.
–Neurologic – Diseases of the brain and spinal cord, such as intervertebral disc disease (IDD or IVDD) that can cause paralysis; strokes; seizure disorders; degenerative myelopathy; myasthenia gravis; encephalitis; laryngeal paralysis; wobbler syndrome; syringomyelia (common in Cavalier King Charles Spaniels); and tumors of the brain and spinal cord.
This category likely includes cognitive disorders as well, such as canine cognitive disorder (CCD) or cognitive dysfunction syndrome (CDS), similar to Alzheimer’s in people. Diseases that cause paralysis, such as tick paralysis, polyradiculoneuritis (coonhound paralysis), and botulism would likely be included in this category.
–Musculoskeletal – Joint problems such as hip dysplasia, elbow dysplasia, and arthritis. Bone cancer would also fall into this category. Trauma is often linked to the musculoskeletal system as well.
–Urogenital – Kidney disease, urinary stones, pyometra (infection of the uterus), and prostate disease. Stones are undoubtedly the major contributor to the Dalmatian’s 16 percent of deaths in this category, and probably a big part of the high rates in Lhasa Apsos, Shih Tzu, and Miniature Schnauzers as well.
(For more information about urinary stones, see “Stoned Again?” in the May 2010 issue of Whole Dog Journal; “Cast in Stone” and “Stone-Free Dalmatians,” in the June 2010 issue; and “A Spotty Response,” January 2011).
–Respiratory – Brachycephalic airway, collapsed trachea, and pulmonary fibrosis. The Afghan Hound is prone to lung lobe torsion, which may account for their high rate of death in this category. Laryngeal paralysis is not uncommon in Vizslas; perhaps that disease was considered respiratory rather than neurologic by the study.
–Hematopoietic – Relating to blood. Causes might include thrombocytopenia (low platelets), autoimmune hemolytic anemia (AIHA), and disseminated intravascular coagulation (DIC). This category could also include blood-related cancers such as leukemia, lymphoma, and hemangiosarcoma.
–Endocrine – Cushing’s disease and diabetes mellitus are the most common endocrine disorders in dogs. Addison’s disease would also fall into this category.
Examples of Disease Processes
Examples of conditions that were likely to be classified into the different disease process categories:
–Trauma – Injury, such as being hit by a car, or being accidentally dropped or stepped on, especially in the case of toy-breed puppies.
–Infectious – Viral disease, such as parvovirus and distemper; bacterial infections, such as leptospirosis and most tick diseases; fungal infections, such as blastomycosis and histoplasmosis; and protozoal disease, such as babesiosis and leishmaniasis.
–Congenital – A condition present at birth, which may be genetic or caused by something that happened in the womb or during birth. Examples include liver shunts, common in the Yorkshire Terrier and Maltese as well as other toy breeds; and heart defects, common in the Newfoundland and Bulldog, among others.
–Degenerative – Diseases such as degenerative disc disease, hip dysplasia, and other forms of joint disease fall into this category. There are also degenerative diseases of the eyes, heart, and other organs.
–Inflammatory – IBD, pancreatitis, masticatory muscle myositis, and granulomatous meningoencepha-lomyelitis (GME) are inflammatory diseases.
–Metabolic – Anything that affects the organs, including kidney and liver disease. Endocrine diseases would be considered metabolic, along with diabetes insipidus and urinary stones.
–Toxic – Poisoning, such as by ingesting rat poison, toxic mushrooms, or antifreeze.
–Vascular – Stroke (cerebral vascular accident) is the most obvious. Other possibilities include acquired liver shunts and fibrocartilaginous embolism (FCE).
You can use this information to help your dog stay healthy.
First and foremost, keep your dog lean! Overweight dogs are more likely to develop musculoskeletal problems, disc disease, diabetes, heart disease, and even some forms of cancer.
Proper vaccination of puppies protects them from most infectious diseases, though frequent revaccination for viral diseases is unnecessary in adult dogs.
Spayed females cannot get pyometra (uterine infection) and neutered males are less likely to develop prostate disease.
Letting dogs off lead only in protected areas helps prevent deaths due to trauma.
Gastropexy (surgery to tack the stomach to the side of the body wall) to prevent torsion and reduce the risk of fatality from bloat can be performed proactively for commonly affected breeds or dogs with close relatives who have bloated, or during bloat surgery.
Even “doggie dementia” can be helped with appropriate supplements and medications (see “Old and Confused,” December 2008). EPA, DHA, antioxidants, and mitochondrial cofactors have been shown to improve the performance of older dogs on various cognitive tasks in as little as two to eight weeks.
Recently it’s been suggested that the high rate of cancer in Golden Retrievers can be partly traced to a single “popular sire” who sired over 1,000 puppies and later died of hemangiosarcoma. Because this dog and his progeny were used so extensively, the genes predisposing Golden Retrievers to hemangiosarcoma are now so widespread that it is difficult to breed around them. Breeders can help ensure genetic variation and avoid such outcomes by not over-breeding to a single dog or line of dogs.
The hope is that, armed with this new knowledge, veterinarians and owners can be proactive in watching for these diseases, taking preventative measures and beginning treatment early. The information from this study can also help direct breed-specific research on genetic causes and preventative measures for specific diseases.
Mary Straus does research on canine health and nutrition topics as an avocation. She is the owner of the DogAware.com website.