The UGA scientists analyzed more than 40,000 canine death records from the 20 year period of 1984 – 2004. The data used came from records in the Veterinary Medical Databases. Analysis of the records showed that intact dogs lived to an average age of 7.9, while neutered dogs lived an average of 9.4 years.
Here comes the surprising part: the study found that spayed and neutered dogs were more likely to pass away from cancer or autoimmune diseases than intact dogs. Could this be partially attributed to the fact that altered canines simply live longer in general and cancer risk factors increase with age?
Intact canines were found to succumb more often to infectious diseases and trauma – conditions often associated with lifestyle.
Jessica Hoffman, co-author of the study, and UGA doctorate candidate, had this to say:
Intact dogs are still dying from cancer; it is just a more common cause of death for those that are sterilized.
UGA veterinarian, Dr. Katie Creevy added the following statement:
At the level of the individual dog owner, our study tells pet owners that, overall, sterilized dogs will live longer, which is good to know. Also, if you are going to sterilize your dog, you should be aware of possible risks of immune-mediated diseases and cancer; and if you are going to keep him or her intact, you need to keep your eye out for trauma and infection.
The authors of the study offered some clarification on the broader cancer findings. For example, the results did show that spaying a female dog before the onset of sexual maturity drastically reduces her chances of developing mammary cancer.
Also, the increased risk of other cancers like lymphoma and osteosarcoma in dogs spayed or neutered before puberty could be due to the fact that they have a tendency to grow taller than intact dogs.
The higher likelihood of death from infections and trauma in intact dogs may be due to their tendency to roam, interact sexually, and fight with other dogs. However, studies on other mammals have also shown an increased susceptibility to infection with higher hormone levels that are present in all intact, sexually mature animals.
Dr. Creevy made a point to add that the population of dogs in the study had been referred to veterinary teaching hospitals, and were already experiencing medical problems. She feels that the average lifespan findings of dogs seen in private veterinary practice would likely be higher, although the trends would remain the same. Creevy said:
…the difference in life span between sterilized and intact is real. The proportionate effects on causes of death are translatable to the global dog population, and it will be interesting to see if explanations for these effects can be found in future studies.
Click here to view the entire published study in the PLOS ONE journal.