Zeuterin™ was carefully evaluated for safety during the process of U.S. Food & Drug Administration approval. However, there is a dearth of objective information on the behavioral effects of neutering male dogs using Zeuterin/EsterilSol—or for that matter, surgical castration—relative to an intact (unneutered) animal. Moreover, there are no published studies on behavior of male free-roaming dogs (FRDs) following either method of sterilization. A team organized by Veterinarians Without Borders/Vétérinaires sans Frontières-Canada (VWB/VSF) aimed to change this.
The study setting: Puerto Natales, a small and isolated city in the Patagonia region of Chile. Like so many other communities across the globe, Puerto Natales struggles with large street dog populations. Not only do many of these dogs suffer serious health and welfare consequences; they also threaten subsistence farmers’ livestock and pose risks to human health in the form of disease transmission, aggression, and dog bites. In short, Puerto Natales was an ideal location in which to support humane dog population control efforts, and with permission from community leaders, to conduct this behavior study.
Using data gathered through over 1,200 hours of video recordings of 118 free-roaming dogs, the team analyzed 57 canine behaviors. The team also used GPS collars to evaluate dogs’ home ranges and tendencies to roam, the latter a behavior commonly believed to diminish with surgical castration and its associated decrease in testosterone production.
The Puerto Natales study demonstrated tremendous variation in dogs’ roaming ranges, which spanned from under half an acre to over 8 square miles (21 square kilometers). Roaming distance was affected positively by higher testosterone and negatively by increasing age; in other words, younger dogs with higher testosterone levels (measured in a companion study) tended to travel further than their older, lower-testosterone counterparts.
Analyses using video recording homed in on four overarching behavioral traits: general activity, social activity, sexual activity, and aggression directed at other dogs. Analyses also spoke to the fact that we cannot assume that surgical or chemical sterilization (or no sterilization at all) will have a consistent impact on a dog’s behavior. For several measures, analysis found no significant behavioral differences between treatments. Analysis also spoke to the importance of inherent (e.g., breed, age, sex, testosterone levels) and environmental (e.g., weather, food, interactions with other people and dogs) factors in influencing behavior. In short, free-roaming dog behavior is complicated!
The work in Puerto Natales is vital to enhancing our appreciation of free-roaming dog behavior and helping people—veterinarians, community members, pet owners, animal welfare experts, and municipal authorities alike—better understand and care for these populations.
(Please note that complete results are currently being prepared for journal publication, and we look forward to sharing detailed findings upon submission.)