Analysis of the impact of trap-neuter-return programs on populations of feral cats

Patrick Foley PhD1, Janet E. Foley DVM, PhD2, Julie K. Levy DVM, PhD, DACVIM3, and Terry Paik DVM4
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  • 1 Department of Biological Sciences, California State University, Sacramento, CA 95819.
  • | 2 Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616.
  • | 3 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.
  • | 4 420 Dewane Dr, El Cajon, CA 92020.


Objective—To evaluate 2 county trap-neuter-return (TNR) programs for feral cat population management via mathematical modeling.

Design—Theoretical population model.

Animals—Feral cats assessed from 1992 to 2003 in San Diego County, California (n = 14,452), and from 1998 to 2004 in Alachua County, Florida (11,822).

Procedure—Data were analyzed with a mathematical Ricker model to describe population dynamics of the feral cats and modifications to the dynamics that occurred as a result of the TNR programs.

Results—In both counties, results of analyses did not indicate a consistent reduction in per capita growth, the population multiplier, or the proportion of female cats that were pregnant.

Conclusions and Clinical Relevance—Success of feral cat management programs that use TNR can be monitored with an easily collected set of data and statistical analyses facilitated by population modeling techniques. Results may be used to suggest possible future monitoring and modification of TNR programs, which could result in greater success controlling and reducing feral cat populations. ( J Am Vet Med Assoc 2005;227:1775–1781)