Studies call neutering of pets into question

For many veterinarians, recommending spaying and neutering comes so easily it hardly merits a second thought. But recent studies out of the University of California Davis and the University of Georgia have challenged that autopilot approach.

In February, researchers at UC Davis published a study in the online journal PLOS ONE that observed the effect of spaying and neutering on the development of certain cancers and joint diseases in golden retrievers. The medical records of 759 client-owned intact and neutered female and male dogs between the ages of 1 and 8 were examined for the diagnosis of hip dysplasia, cranial cruciate ligament tear, lymphosarcoma, hemangiosarcoma and mast cell tumor. The dogs were classified as intact, early-neutered (before 12 months old) and late-neutered (at or after 12 months old).

All five diseases were found to be significantly higher in the neutered population. One of the most dramatic findings was that 10 percent of early-neutered male dogs were diagnosed with hip dysplasia, twice the percentage seen in intact males. Early neutering was also associated with an a greater incidence of cranial cruciate ligament tear and lymphosarcoma in male dogs and cranial cruciate ligament tear in females. There was also a greater occurrence of mast cell tumor and hemangiosarcoma in late-neutered compared with intact females.

Comparatively, the study out of the University of Georgia, also published in PLOS ONE, looked at a sample of more than 40,000 canine death records to determine the effect sterilization may have on both lifespan and cause of death, while controlling for the effects of age. The results showed that while sterilization increased the lifespan of dogs, it also increased the risk of death from cancer or autoimmune diseases. However, researchers recognized that a direct link between sterilization and the study outcomes could not be made, as a number of unknown factors, including the age at which the animal was sterilized, potentially added bias to the results.

Neuter or not?

Given the results of these studies, some veterinarians are wondering if they should alter their message promoting spaying and neutering of dogs and cats. Karen Overall, VMD, PhD, DACVB, a well-known author and speaker on behavioral medicine, was immediately concerned upon seeing the results of the UC Davis study. "Now everybody is going to stop neutering their dogs," she thought.

But after reviewing the study results and consulting with colleagues about it, Overall isn't wavering in recommending spaying and neutering to pet owners. She will, however, continue to emphasize the importance of treating each pet as an individual case.

"If an animal is going to go out and get into fights because it's intact, that case requires intervention. That animal is going to roam and fight and get hit by a car. We've done that animal no favors by not neutering it," she says. "On the other hand, if that animal doesn't display any of those behaviors, then we should go through the relative risks and medical concerns of not neutering with the owner."

Jessica Vogelsang, DVM, a veterinary blogger and contributing author for a number of publications, also pored over the study results and came to a similar conclusion—each case should be considered individually. Vogelsang notes in her blog, pawcurious.com, that while many intelligent, educated pet owners will make an informed decision whether or not to neuter, there are pet owners who make less informed if not poor decisions about pet care. If an owner isn't interested in basic preventive care and training, she's concerned that this person won't be responsible with an intact pet. For those owners, her recommendation to spay or neuter the pet is a given.

Stay on task

Although Overall's and Vogelsang's approaches to spaying and neutering won't be affected by the results of the UC Davis study, Overall is concerned that the study outcomes may leave many veterinarians on unsteady ground with regard to their recommendations. "What worries me is that veterinarians aren't going to have good answers for pet owners and clients," she says. "I'm worried this study is going to take a lot of energy out of the conversation that we've worked so hard to deliver."

Concerns aside, Overall stresses that veterinarians should focus on each animal individually and take quality of life, safety and public responsibility into account as they evaluate and make recommendations. With this mindset, they really can't go wrong.