Modelling sterilisation strategies to maximise population impact and cost-efficiency in free-roaming dog populations
Free-roaming dog populations pose challenges to public health and animal welfare, and their management and protection is legally mandated in many countries to control zoonotic diseases such as rabies, reduce bites, mitigate fear of aggressive dogs, and preserve animal welfare. Although international organisations recommend holistic dog population management with surgical sterilisation as a key component, stakeholders report a lack of evidence-based guidance on effective and cost-efficient strategies. To address this, we developed a deterministic model of a closed free-roaming dog (FRD) population, including dogs dependent on and independent of humans, parameterised using data from southern India. We evaluated a wide range of sterilisation strategies varying duration, interval, frequency, intensity, targeting different population subsets, and fixed or responsive approaches. Strategies were assessed based on their effects on independent FRD population size and implementation costs. Female sterilisation coverage (FSC) strongly determined population reduction and cost-effectiveness. Repeated, short sterilisation periods with appropriately timed intervals and high early intensity best balanced population reduction and cost-efficiency. Excluding dependent dogs (cared for by humans) severely constrained population reduction, while male sterilisation enhanced impact at little extra cost, assuming direct effects on pregnancy rates. Costs and population impacts can be visualised on an interactive web application (https://field.shinyapps.io/DogPopSimApp), allowing practitioners and policymakers to explore sterilisation strategy outcomes. Overall, cost-effective population reduction required sustained commitment and coverage-driven strategies that balance welfare, population reduction and the operational needs of dog-mediated rabies control. Author SummaryFree-roaming street dogs live closely with people. While these animals are often valued members of the community, they can raise public health and safety concerns, including disease transmission, bites, and traffic accidents. To protect both human and animal health, many regions use surgical sterilisation to humanely manage street dog populations. However, running these programmes is complex and expensive, and community managers often lack clear guidance on how to maximise their limited resources. To address this, we used data from southern India to create a mathematical model of a street dog population. We simulated thousands of different sterilisation strategies to see how factors like campaign length, frequency, and targeted sub-groups impacted population size and total costs. We found that short, repeated sterilisation campaigns offer the best balance of population reduction and cost-efficiency. Crucially, these programmes must include dogs that are partially cared for by humans; otherwise, their puppies will continually replenish the street population. Although sterilisation of females drives population reduction, sterilising males alongside females enhanced the overall impact. Ultimately, our study provides practical, evidence-based guidance to help communities design effective and financially sustainable dog management programmes that improve public health and animal welfare.