What is it about?
Most shelters sterilize animals before they go home, and surgery capacity is limited. On any given surgery day, some animals get a slot and others wait for the next one. Which animals should go first? This study models what that wait costs, measured as the extra days an animal spends in the shelter. The cost depends on three things: how long the animal must wait for the next surgery day, how willing adopters are to commit to an animal before surgery, and the animal's own expected length of stay. The first two combine into a single number - the adoption opportunity available during the wait, measured in days. That one number decides which animals a shelter should prioritize, and whether the choice matters at all.
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Photo by Karsten Winegeart on Unsplash
Why is it important?
Length of stay drives a shelter's census, and census drives crowding, staff workload, and the quality of care. Shelters should avoid unnecessarily longer stays. An existing informal guideline tells shelters to prioritize fast-track animals - those expected to be adopted quickly - for surgery and other needed procedures. Nobody had checked when that guideline actually holds, or how much difference it makes. The model shows it holds when the adoption opportunity exceeds one day, and that the benefit is concentrated among animals with short to medium expected stays. Past about 20 days, the choice makes little difference. When the adoption opportunity falls below one day, the preference reverses direction - but so weakly that it's better to ignore it altogether. The guideline is sound in some circumstances and close to meaningless in others. A shelter can tell which situation it is in, using numbers it already has.
Perspectives
Shelters make these decisions often, usually by informal reasoning. I wanted a model simple enough for a shelter to actually use. The contrast with my earlier work on marketing is striking. There, the answer was to promote the slow-track animals, the ones least likely to be adopted (https://link.growkudos.com/1f1qj51rd34). But on surgery slots, the answer often runs the other way. Different resources behave differently, and intuition carried over from one to the other can mislead. A practical recipe falls out of the model. Take the interval between your surgery days - say a week for a smaller shelter - and multiply it by your best guess of the fraction of adopters willing to commit to an animal before surgery. If the product is well above 1 and you have candidates with short expected stays, prioritize them; the gain can be a few days of stay per animal. If it is near or below 1, the choice barely matters, and you can decide some other way. There is a second lever here that is easy to overlook. The more adopters are willing to commit before surgery, the less the wait costs - especially for the animals that would otherwise stay longest. Keeping unsterilized animals visible and adoptable, and reassuring adopters about the wait, is itself a way to shorten stays. Be careful in informal thinking about length of stay. It is tempting to think that an animal expected to take 10 days to adopt will take 10 days regardless, so a 3-day wait costs nothing. That reasoning is wrong: adoption is a chance process, and an adoption opportunity lost during the wait shows up, on average, as a longer stay.
Michael Mavrovouniotis
Social Compassion / SCIL
Read the Original
This page is a summary of: Guidelines for the prioritization of adoptable shelter animals for sterilization to reduce average length of stay: a mathematical model, American Journal of Veterinary Research, September 2026, American Veterinary Medical Association (AVMA),
DOI: 10.2460/ajvr.26.06.0270.
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