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.

Objective: To examine rates of overweight or obese (OvOb) body condition score, including the association between OvOb and gonadectomy, in 15 dog breeds.

Methods: The analysis considered the 5 most recorded large breeds (26,369 dogs) and 10 most recorded toy/small breeds (90,002 dogs) in Banfield Pet Hospital's database from 2013 to 2019. Cox proportional hazards models evaluated associations between OvOb and gonadectomy status, gonadectomy age, sex, and primary breed. Models estimated OvOb rates in gonadectomized versus intact dogs of each breed and, separately, OvOb rates according to gonadectomy age.

Results: There was substantial breed variation in underlying (intact dog) OvOb rates among the 15 breeds. Pugs, Golden Retrievers, and Labrador Retrievers had highest underlying susceptibility to OvOb outcomes. There was some variation in relative OvOb rates among breeds, but breeds differing substantially from size group peers were limited. Among all toy/small breeds, gonadectomy at 3 or 6 months had hazard ratios (relative risks) lower than, or not statistically different from, gonadectomy at 1 year or older. For large dogs, OvOb outcomes associated with prepubertal gonadectomy varied by breed.

Conclusions: Underlying susceptibility to OvOb varies by breed. Gonadectomy offers significant benefits at individual and population levels. As with many veterinary care decisions, however, there is complexity, and associated OvOb risks are not uniform across breeds.

Clinical relevance: Results may facilitate more individualized recommendations for gonadectomy timing and proactive strategies (specifically diet and exercise) to mitigate risk of OvOb outcomes, while accounting for the broader context of individual dog and population-level benefits of gonadectomy.