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Modeling of Effect of PAUSE on TNR Programs: An ACC&D Video Report

As a result of the COVID-19 pandemic, many organizations who engage in feral, community and shelter cat spay-neuter programs halted their surgical operations. In late February and early March, the unknown virus levels and spread in our community, the scarcity of surgical supplies and PPE, and the fear of feline SARS-CoV-2 infections caused uncertainty about continuing with normal operations. Many organizations agonized over this choice and worried that years of hard fought spay-neuter progress would unravel. So, did it?

Although the empirical data is not yet in, epidemiological modelers working with the Alliance for Contraception for Cats and Dogs (ACC&D) have created a short video report about using their supercomputing skills to try and answer that question. Epidemiological models take selected elements of an ecosystem and try to predict what will happen when conditions are manipulated. You may recognize one of these models as the viral pandemic “infection curve,” steep when people gather as usual, and flatter when citizens wear masks, wash hands, and physically distance. The same sort of graph can be used to describe the effects on a cat population when a spay-neuter program is enacted.

What the ACC&D modelers illustrated was this: High intensity targeted TNR programs — defined as 75% sterilization of a cat population with re-captures every 6 months — maintain the cat population level at about 50-60% of their pre-program population after a few years. If the year-long pause is in year 2 or later of the TNR program, the cat population does not grow much at all (~5%). All growth is from emigration, abandonment, or one or two un-captured females having litters. And it takes only one subsequent year to bring the population back down to pre-pause levels.

Lower intensity TNR programs — defined as sterilizing only 25% of one cat population with recaptures every 6 months — generally maintain the cat population level at about 70-80% of their pre-program population after a few years. A year-long pause in these programs adds more cats (~10%,) because more of the population is fertile, but emigration and abandonment can also play a part. Because of the lower intensity of trapping, it takes a couple more years to catch up. The good news is that increasing the intensity of trapping easily makes up for that lost time, and doesn’t cost any more in the long term.

These models are heartening theoretical evidence that pausing to catch our breath and gather information about COVID for a few months will not erode our years of spay-neuter work. They also illustrate the importance of intensive targeting for TNR programs if population reduction is the main goal; the greater the proportion of a population we can sterilize and maintain, the more lasting and effective that intervention will be in the long run.

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