Spay and Neuter Negatives

By Amy Fernandez


For decades, spay/neuter has been widely advocated as socially responsible and beneficial to a pet’s health. Although these ideas are constantly reinforced in the media and endorsed within the veterinary community, there was no scientific evidence to validate them. That has changed over the past decade as researchers began reviewing lifetime health records of neutered pets. Cursory findings prompted more than 20 significant studies to evaluate the risks and benefits of these procedures. The data challenged widely held assumptions that these procedures improve overall health and reduce cancer risks.


Multiple studies revealed higher incidences of certain cancers such as ocsteosarcoma, hemangiosarcoma, and the unexpected discovery of prostate cancer rates up to four times higher in castrated dogs. Although neutering was not considered to cause prostate cancer, researchers theorized that altering the animal’s hormone balance interfered with natural immune response that normally inhibited tumor progression. Likewise, higher incidences of adverse vaccine reactions were also attributed to altered immune function. The complex physiological changes of spay/neuter surgery were also linked to a wide variety of disorders such as hypothyroidism, orthopedic disorders, obesity, and urinary incontinence.
Although this information was published in veterinary journals for years, it wasn’t widely accepted. In part, that’s because most studies extrapolated information from large random dog populations that represented a wide spectrum of purebreds, mixed breeds, dogs, bitches, puppies, and adults, all neutered at different ages. This precluded the possibility of analyzing the results based on gender and age-of-neutering.


A new study out of the University of California-Davis published earlier this year is the first to focus on this issue within a single breed, one of America’s most popular, the Golden Retriever. Headed by Dr. Benjamin L. Hart, professor emeritus at the UC-Davis School of Veterinary Medicine, the team analyzed medical records for 759 Golden Retrievers ranging from one to eight years that had been treated at their Veterinary Medical Teaching Hospital for hip dysplasia, cranial cruciate ligament tear, lymphosarcoma, hemangiosarcoma, or mast cell tumor. For the study, they were classified as sexually intact, neutered before 12 months of age, or neutered at one year or later.


Regardless of age of neutering, both dogs and bitches demonstrated significantly higher rates for all five conditions compared to the sexually intact control group. The UC Davis study was the first to document a higher incidence of mast cell tumors and hemangiosarcoma associated with late neutering.


Approximately seven percent of bitches spayed at one year or later that developed hemangiosarcoma, more than four times the rate for this disease noted in the sexually intact group and bitches spayed before one year of age. None of the sexually intact bitches developed mast cell tumors, compared to six percent that were spayed at one year or later.


Although pediatric spay/neuter has fallen from favor, it is still aggressively promoted by animal rights groups and endorsed by the AVMA. The UC Davis study revealed a significantly higher incidence of hip dysplasia in dogs neutered before one year of age compared to the rate of occurrence noted in the sexually intact males. None of the intact dogs or bitches developed cruciate ligament tears, compared to five percent of the dogs and eight percent of the bitches neutered before one year of age. Lymphosarcoma was diagnosed in almost 10 percent of males castrated early, three times the rate noted in sexually intact males.


The results also questioned the conventionally accepted practice of spaying bitches before their first or second season to minimize the risk of mammary cancers. None of the 120 intact bitches in the UC Davis study developed mammary cancer and two cases were diagnosed in spayed bitches. Likewise, the results contradicted the notion that neutering after maturity has limited impact to curb sex linked behavior problems like aggression and territorial marking. Neutering males in adulthood proved no less effective.


In most areas, this study did not reveal any significant new information about the increased disease risks that have already been linked to spay/neuter surgery. But it does provide a much clearer picture of its specific impact on the health of this breed. Hopefully, it will become a model for similar research on other breeds and provide dog owners with valid information to make informed decisions.