How connections between obesity, nontraumatic orthopedic injuries and gonadectomy in large-breed dogs can impact conversations between you and your clients

For decades, gonadectomy has been promoted to both pet owners and veterinarians in North America for its various health benefits, and as a critical tool for combating pet overpopulation. It’s widely seen as an important component of responsible pet ownership.

Gonadectomy, though, is receiving increased scrutiny as veterinary medicine continues to embrace evidence-based recommendations. Over the last 10 years, researchers have attempted to find answers regarding the optimal timing of sterilization of dogs, while balancing the positive and negative health outcomes of gonadectomy with the very real problem of pet overpopulation. Study results have been inconsistent, with some studies in conflict with current recommendations and other studies in conflict with each other. While the science is far from settled, there are still takeaways that can inform the conversation veterinarians have with owners around the timing of gonadectomy for their dogs.

Obesity has become a major health issue in dogs, with estimates of up to 60% of dogs in the United States either overweight or obese. The list of diseases associated with obesity in dogs is legion and recent data suggests overweight, gonadectomized dogs have shorter life spans. Although gonadectomy has been associated with the development of overweight or obesity, the association between age at gonadectomy on overweight or obesity has produced conflicting results.

Questions surrounding gonadectomy and nontraumatic orthopedic injuries likewise have produced similarly conflicting results. Many veterinarians now recommend delaying gonadectomy in large-breed dogs, with these recommendations often based on personal experience and anecdotal evidence. While many plausible causal mechanisms exist to explain why gonadectomy may be associated with joint injury and disease, the scientific literature provides conflicting results.

The evidence surrounding cancer risk and gonadectomy is even more tangled. Although the link between early spaying and the development of mammary cancer is well known, other studies point to conflicting results when it comes to reproductive hormones and cancer.

A large Australian study published in 2018 showed that gonadectomized dogs (of both sexes) were at a higher risk for lymphoma compared to their intact counterparts. Another study looking at golden retrievers in California, also published in 2018, did not find a difference between gonadectomized and intact males in regard to cancer-related mortality, but did demonstrate a difference between intact and spayed females with more spayed females dying of cancer than males. An earlier study looking at a population of golden retrievers in California found that gonadectomy in either males or females increased the risk of several different types of cancers when compared to intact dogs. Lastly, a paper published in 2014 demonstrated that gonadectomized vizslas had increased odds of developing cancer than their intact counterparts.

Morris Animal Foundation recently published a study on the effect of gonadectomy on the incidence of obesity and overweight, and nontraumatic orthopedic injury using data from their Golden Retriever Lifetime Study. This longitudinal study is collecting data on more than 3,000 dogs as they mature from puppyhood through adulthood to better understand the risk factors for cancer and other diseases in dogs.

For the spay/neuter study, the team divided their cohort into four age groups: dogs under 6 months of age at gonadectomy; dogs 6 months to 12 months of age at gonadectomy; dogs over 1 year of age at gonadectomy; and intact dogs. Results showed that gonadectomized dogs in all categories had an increased risk of obesity and overweight compared to the intact group. For nontraumatic orthopedic injuries (in this study cranial cruciate ligament rupture and arthritis), only dogs gonadectomized under 6 months of age had an increased risk of these conditions.

“These findings emphasize that the timing of gonadectomy may impact future health outcomes, both in positive and negative ways.” said Dr. Missy Simpson, lead author of the paper and Staff Epidemiologist for the Golden Retriever Lifetime Study. “These results are especially powerful because we were able to verify that gonadectomy preceded overweight/obesity and orthopedic injury. Establishing the order of events is important because we can rule out reverse causality as an explanation for our findings. In other words, owners’ decision to spay or neuter their dogs was not a result of the outcomes we studied.”

Recommendations about the timing of gonadectomy represent one facet of a trend toward personalized medicine in both veterinary and human health care. As we learn more about the effect of reproductive hormones on health, we’ll be better able to guide our clients and improve health and longevity in our patients.

Learn more about the Golden Retriever Lifetime Study at morrisanimalfoundation.org or listen to a podcast about the spay/neuter study.