Robert J. McCarthy , DVM, MS, DACVS ; Stephen H. Levine , PhD ; J. Michael Reed , PhD

Department of Veterinary Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536. (McCarthy); Department of Civil and Environmental Engineering, School of Engineering, Tufts University, Medford, MA 02155. (Levine); Department of Biology, School of Arts and Sciences, Tufts University, Medford, MA 02155. (Reed)

Objective—To predict effectiveness of 3 interventional methods of population control for feral cat colonies.

Design—Population model.

Sample—Estimates of vital data for feral cats.

Procedures—Data were gathered from the literature regarding the demography and mating behavior of feral cats. An individual-based stochastic simulation model was developed to evaluate the effectiveness of trap-neuter-release (TNR), lethal control, and trap-vasectomy-hysterectomy-release (TVHR) in decreasing the size of feral cat populations.

Results—TVHR outperformed both TNR and lethal control at all annual capture probabilities between 10% and 90%. Unless > 57% of cats were captured and neutered annually by TNR or removed by lethal control, there was minimal effect on population size. In contrast, with an annual capture rate of ≥ 35%, TVHR caused population size to decrease. An annual capture rate of 57% eliminated the modeled population in 4,000 days by use of TVHR, whereas > 82% was required for both TNR and lethal control. When the effect of fraction of adult cats neutered on kitten and young juvenile survival rate was included in the analysis, TNR performed progressively worse and could be counterproductive, such that population size increased, compared with no intervention at all.

Conclusions and Clinical Relevance—TVHR should be preferred over TNR for management of feral cats if decrease in population size is the goal. This model allowed for many factors related to the trapping program and cats to be varied and should be useful for determining the financial and person-effort commitments required to have a desired effect on a given feral cat population.