Project inspiration

Surgical sterilization is widely accepted in certain countries, including the U.S., and it can be essential for humanely managing dog and cat populations. But for dogs in particular, it can be hard to determine risks and benefits of surgery at the individual level, and especially the best age to sterilize different “types” of dogs (e.g., different sizes, breeds with varied risk factors).  

Several studies have explored this topic, but there are unanswered questions about the relationship between sterilization and later health/behavior problems. Some prior studies also limit their research to specific breeds, or to only purebred dogs, or to dogs seen in a specialty veterinary clinic. As a result, the findings simply can’t represent the full population of dogs. 

ACC&D wants to better understand the “baseline” health implications of surgical sterilization. Once we do this, we’ll be in a better position to evaluate how future non-surgical sterilants will compare. This will support veterinarians and pet guardians considering the benefits and risks of new technologies, plus allow for more individualized veterinary care for dogs who have varied needs and risk factors.  

What we’re doing

ACC&D has convened a team of experts and partnered with Banfield Pet Hospital to explore questions around surgical sterilization and health outcomes in dogs. Banfield is the leading provider of preventive veterinary care in the U.S., and its more than 1,000 clinics use the same record-keeping system. This yields a large amount of high-quality data from dogs across the country, which can then be used (following anonymizing of data, plus ethical reviews and approvals) to help improve medical care for current and future animals.  

Analysis #1

The team published “Age at gonadectomy, sex, and breed size affect risk of canine overweight and obese outcomes: A retrospective cohort study using data from United States primary care veterinary clinics” in the Journal of the American Veterinary Medical Association in May 2023. You can download it at no cost here.

Companion animals in many industrialized countries are facing an obesity epidemic. In a new unpublished analysis, Banfield found a 13% increase in dogs diagnosed as overweight or obese over a two-year period, jumping from 38% of dogs seen in 2020 to 43% in 2022, and research (here and here) has found the prevalence of canine O/O to approach 60%. Obesity can reduce quality of life, and it is also associated with other health conditions, some of them fatal if left untreated.

Addressing pet obesity requires considering many factors, one of which is sterilization—and particularly the age that dogs are sterilized. With a sample of over 155,000 dogs tracked for up to seven years, we compared outcomes for sterilized versus intact dogs, and then also looked at whether the age at which dogs were sterilized affected their risk of an overweight or obese body condition score (a standardized measure used in the veterinary profession). You can view major study findings in the ACC&D press release and Banfield Exchange article. 

Analysis #2

In May 2025, the team published “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” in the Journal of the American Veterinary Medical Association. Authors analyzed anonymized data of over 116,000 dogs seen at Banfield in 2013-2019 to study the relationship between sterilization and overweight or obese (OvOb) outcomes. The present paper investigates 5 popular large breeds and 10 popular toy/small breeds: Labrador Retriever, German Shepherd, Boxer, Golden Retriever, American Bulldog, Yorkshire Terrier, Chihuahua, Shih Tzu, Maltese, Poodle, Pomeranian, Dachshund, Miniature Schnauzer, Pug, and Bichon Frise.

Key findings include:

• There is substantial breed variation in underlying OvOb rates for intact dogs; Pugs, Golden Retrievers, and Labrador Retrievers had the highest underlying susceptibility.

• There was some variation in relative OvOb rates among breeds following sterilization, but breeds differing substantially from size group peers were limited.

• Among toy/small breeds, the relative OvOb risk among dogs sterilized before puberty was no higher than for dogs sterilized at 1 year of age or older. For large dogs, OvOb outcomes associated with prepubertal sterilization varied by breed.

More details are available in the Mars Veterinary Health press release. Contributors to the research represent the Alliance for Contraception in Cats & Dogs; Mars Veterinary Health, including Banfield; Virginia-Maryland College of Veterinary Medicine Department of Population Health Sciences; Jonsson Comprehensive Cancer Center, University of California, Los Angeles; Hunter College Program in Animal Behavior and Conservation; and University of Padova Department of Animal Medicine, Production and Health. 

Project funding

The Morris Animal Foundation is generously funding the two preliminary analyses and resulting publications (Grant ID D22CA-513).