ACC&D study published in PLOS ONE 

News Release - for immediate release 

Contact: Joyce Briggs, President, ACC&D,, 503-358-1438

New Study Models Intervention Options to Manage Free-Roaming Cat Populations: Research generates guidance to provide communities with practical tools for effective programs

FRC--webPortland, Oregon (December 9, 2014): A new study confirms that free-roaming cat populations can be reduced by fertility control if performed at sufficiently high intensity. “Simulating Free-Roaming Cat Population Management Options in Open Demographic Environments,” published in the peer-reviewed open-access journal PLOS ONE, uses sophisticated computer modeling techniques and best available scientific data to explore the effectiveness of different population management approaches.  

The effort is a collaborative effort by experts in wildlife conservation and cat protection, dedicated to getting beyond the gridlock created by polarizing views that policies must choose between protecting wildlife or cats.  The study offers new insights, based on realistic data, on options for responsibly managing free-roaming cat populations.


The model shows that a TNR (Trap-Neuter-Return) program in a typical area needs to surgically sterilize a minimum of 40 percent of all fertile cats in a defined population at six-month intervals to achieve long-term decline in population abundance. This is equivalent to maintaining a cumulative sterilization rate of about 75 percent. Achieving the same level of population control by traditional methods requires removing a minimum of 30 percent of all cats at each interval. 

Multi-year non-surgical contraception offers promise for free-roaming cats due to these cats’ shorter lifespans relative to owned cats and the appeal of an injectable treatment that costs much less than surgery. The model shows that a three-year contraceptive, which is currently under development, performs nearly as well as surgical sterilization at the same 40 percent semi-annual treatment rate over an initial five-year period but requires an elevated treatment rate of at least 50 percent to prevent population growth over the longer term. 

“This is the most comprehensive simulation-based study to date of free-roaming cat population dynamics and management,” says lead author Philip Miller, PhD, wildlife conservation biologist with the IUCN’s Conservation Breeding Specialist Group. “Unlike prior analyses, this model evaluates population management options while also accounting for entry of fertile cats into the managed population through dispersal and owned cat abandonment, specific modes of density-dependent survival, and habitat-specific cat demography.”

Additional new resources:  

Investigators have created two additional resources, available free of charge. The first distills model findings into a practical Guidance Document. The second, "A Generalized Population Monitoring Program to Inform the Management of Free-Roaming Cats," advises on determining and monitoring cat population numbers to evaluate intervention impact.  

“Our study demonstrates that adding even small numbers of fertile cats to a population, such as abandoned pets, dramatically reduces the efficacy of a strong management program,” shares Margaret Slater, DVM, PhD, ASPCA veterinary epidemiologist and co-investigator. “Efforts to encourage people to provide basic care for cats including spaying or neutering them is an important piece of the puzzle.”

Next steps:

Economic and social considerations need to be combined with biological factors to determine the best management option(s) for individual communities. According to John Boone, PhD, wildlife biologist, ACC&D Board member and co-investigator, “We are currently modeling combinations of interventions and factoring in cost-effectiveness. For example, kittens might be removed from colonies for socialization and rehoming; cats who aren’t candidates for adoption would be sterilized and returned. A multi-year contraceptive could initially be used to treat more cats at a reduced cost. Managing outdoor cats is challenging, and it is critically important that we find the approaches that offer the best chance for success.”

About the study collaborators*

This study is the product of an unprecedented joint effort by experts in cat welfare, wildlife conservation and veterinary medicine. Participating scientists came from the Alliance for Contraception in Cats & Dogs (ACC&D); The ASPCA® (The American Society for the Prevention of Cruelty to Animals®); Cummings School of Veterinary Medicine at Tufts University; Great Basin Bird Observatory; Illinois State Museum; International Union for Conservation of Nature - Conservation Breeding Specialist Group (CBSG); and University of Florida College of Veterinary Medicine. ACC&D coordinated this study; the work was made possible by a grant from the ASPCA.

About ACC&D

ACC&D is a nonprofit organization whose mission is to expedite the successful introduction of methods to non-surgically sterilize dogs and cats and to support distribution and promotion of products to humanely control cat and dog populations worldwide. For more information, visit  

*The statements made in this press release do not necessarily represent official positions of CBSG, SSC, or IUCN, or other organizations mentioned.