New Study Reveals Breed-Specific Obesity Risks After Dog Neutering—Timing Matters

Gonadectomy Status and Age Are Associated With Variable Risk of Overweight or Obese Outcomes in 15 Dog Breeds: A Retrospective Cohort Study Using Data From Primary Care Veterinary Clinics

Valerie A. Benka, John M. Sahrmann, Katherine Rieke, Joyce R. Briggs, Nathaniel Spofford, Stephen Zawistowski, Audrey Ruple, Stefano Romagnoli, Jo Ann Morrison

Background
Gonadectomy (spay/neuter) is a common veterinary procedure with known health benefits, including preventing unwanted litters and reducing specific reproductive diseases. However, previous research has indicated an association between gonadectomy—particularly when performed at certain ages—and increased risk of obesity in dogs. This study aims to evaluate breed-specific variations in the risk of overweight or obese (OvOb) outcomes relative to gonadectomy status and age at the time of surgery.

Methods
This retrospective cohort study analyzed electronic medical records from Banfield Pet Hospital clinics (2013–2019), focusing on 15 dog breeds (10 toy/small and 5 large breeds) with the highest representation. Dogs were categorized based on gonadectomy status and age at surgery, with outcomes measured using body condition score (BCS). Cox proportional hazards models assessed the relationship between gonadectomy variables and OvOb outcomes, adjusting for covariates like breed, sex, weight, and preventive care enrollment.

Results
There was significant breed-based variation in OvOb risk. Pugs, Golden Retrievers, and Labrador Retrievers had the highest baseline OvOb susceptibility. In toy/small breeds, early gonadectomy (3–6 months) was associated with either a lower or similar risk compared to surgery at 1 year. In contrast, early gonadectomy increased OvOb risk in several large breeds, especially in Labrador and Golden Retrievers. Across all breeds, gonadectomy was linked to higher OvOb rates compared to remaining intact, with the effect more pronounced in males.

Limitations
The study could not account for environmental and behavioral variables such as diet and exercise. Breed designation relied on medical record entries, which may lack precision, especially for mixed breeds. The analysis excluded dogs not at an ideal BCS at baseline, which may limit generalizability. Additionally, sample sizes for some subgroups were small, affecting confidence in breed-specific estimates.

Conclusions
The risk of obesity following gonadectomy is not uniform across breeds and varies with age at surgery. For toy/small breeds, early gonadectomy does not appear to increase obesity risk and may be safer in this regard than later procedures. However, in some large breeds, delaying gonadectomy until at least 1 year of age may reduce obesity risk. These findings support individualized decision-making about gonadectomy timing based on breed-specific risk profiles.

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