Per capita shelter intake and euthanasia have been in a steady decline nationwide for the past several decades. Research has indicated that one reason for this decline is the increasing incidence of spayed and neutered animals in the pet population (Zawistowski et al., 1998; Irwin, 2001; Clancy & Rowan, 2003, Miller et al, 2014). In fact, the veterinary community recently formally acknowledged the importance of safe, efficient, accessible sterilization programs as the “best antidote to the mass euthanasia of cats and dogs resulting from overpopulation” (Looney et al., 2008). However, this decline has not been uniform; levels of shelter intake and euthanasia vary across communities and are different for dogs and cats. As a result, many communities are currently searching for methods to reach those who are still contributing disproportionately to companion animal homelessness. Attempts to reduce shelter intake and euthanasia through the passage of legislation mandating the spaying and neutering of companion animals has recently garnered much attention and debate.
To the knowledge of the ASPCA, the only humane method of population control that has demonstrated a correlation with long-term efficacy in significantly reducing the number of animals entering animal shelters is the voluntary sterilization of owned pets (Clancy & Rowan 2003; FIREPAW, 2004; Secovich, 2003).There is also evidence that sterilizing very specific, atrisk sub-populations of companion animals, such as feral cats and animals in shelters, contributes to reductions in population (Zawistowski et al., 1998; Clancy & Rowan 2003; Levy et al., 2003; Lord et al., 2006; Natoli et al., 2006). However, the ASPCA is not aware of any credible evidence demonstrating a statistically significant enhancement in the reduction of shelter intake or euthanasia as a result of the implementation of a mandatory spay/neuter law of general application to all owned animals within a community. Indeed, mandating spay and neuter for owned pets can have the unintended consequences of increasing shelter intake and impeding the return of strays to their owners when the costs associated with spay and neuter are prohibitive.
Caution must therefore be applied when interpreting existing claims regarding the effects of local mandatory spay/neuter (MSN) laws. First, because per capita shelter intake and euthanasia are in decline due to a variety of reasons, it is impossible to determine the effect of an MSN law without comparing a community’s trends in shelter intake and euthanasia for several years before and after the law was enacted to trends in adjacent, similar communities without MSN legislation. Furthermore, to determine with confidence the effects of any spay/neuter program on the animal population, which naturally fluctuates somewhat from year to year, population trends must be examined over a period sufficiently long to absorb those natural fluctuations. Claims based on one or two years of data can be misleading.
In addition, it is imprudent to generalize about the effects of MSN laws. One reason is that the definition of “mandatory” varies greatly across communities. In some localities, a citation may be 2 issued for any animal over the age of four months seen unaltered, while in other communities, a citation results only when another animal control offense has been committed or if more than one intact female lives in the household. Another complication is that it can be extremely difficult for even a veterinary professional to visually determine if an animal, particularly a female, has been sterilized; it would be virtually impossible for an animal control officer to make those determinations in the field. For these reasons and due to variation across communities in law enforcement funding and personnel support, actual enforcement of MSN laws varies widely, making comparisons between MSN laws or predictions about their impact very difficult.
Another reason for caution when interpreting the effects of MSN legislation is that shelter intake and euthanasia statistics are often presented as a total number of dogs and cats. In some communities, the number of dogs entering and being euthanized in shelters is dropping significantly while the number of cats is declining more slowly or even increasing. Therefore it is critical to examine population and shelter statistics for dogs and cats separately, so that reductions in dog intake and euthanasia do not mask increases in cat intake and euthanasia. This issue is particularly critical in the analysis of the effect of MSN laws, since feral and unowned stray cats continue to represent a substantial proportion of the shelter population and euthanasia at shelters. This major contributing factor is not addressed by MSN laws that, by nature, target owned animals.
Even when an MSN law seems to have a positive effect on one aspect of animal welfare, it may have a negative effect on another. For instance, in at least one community that enacted an MSN law, fewer pets were subsequently licensed, likely due to owners’ reluctance to pay either the high fee for keeping an unaltered animal or the fee to have the pet altered (Office of Legislative Oversight, 1997).
The ASPCA is also concerned that some communities may rely primarily or exclusively on MSN legislation to reduce shelter intake and euthanasia even though the animal shelter population is actually very heterogeneous with no single cause or source (National Council on Pet Population Study and Policy, 2001, American Humane Association, 2013, Weiss et al 2014). Many social, cultural and economic factors as well as animal health and behavioral issues contribute to shelter intake; therefore, no single program or law can be relied on to solve the problem.
Furthermore, one of the main barriers to spaying and neutering of pets is accessibility of services, which is not addressed simply by making spaying and neutering mandatory. Cost is one of the primary barriers to spay/neuter surgery in many communities (Patronek et al., 1997; Ralston Purina, 2000; Frank, 2001). In fact, low household income and poverty are statistically associated with having a sexually intact cat (Patronek et al, 1997; Chu et al., 2009), with relinquishment of pets to shelters (Patronek et al., 1996), and with shelter intake (Frank, 2003). Recent research indicates that intake into shelters is greatest from areas where human poverty levels are high (Miller, et al 2014; Patronek, 2010). As a result, a higher proportion of pets from impoverished communities are entering shelters, and data suggests that these pets may be at a significantly higher risk for euthanasia (Patronek, 2010).
Each community is unique, however, in terms of the particular sources and causes of companion animal homelessness and the primary barriers that exist to having pets altered. No one-size-fits-all solution is therefore possible. In examining communities around the country that are having significant success in reducing companion animal homelessness, it appears that the common denominator is a multifaceted, targeted community program that:
- is based on careful research to determine which segments of the animal population are actually significantly contributing to shelter intake and euthanasia and then targets efforts to those segments of the population;
- focuses on the particular barriers to spay/neuter that are predominant and strives to overcome them;
- is well-supported and well-funded; and- has an efficient voluntary spay/neuter infrastructure in place to service the populations it targets.
The ASPCA does not support laws that mandate spay/neuter of all owned animals within a community; however, based on currently available scientific information, the ASPCA strongly supports spay/neuter as an effective means to reduce shelter intake. In particular, the ASPCA supports voluntary, affordable, accessible spay/neuter programs for owned pets, Trap-NeuterReturn (TNR) programs for feral cats and the mandatory sterilization of shelter animals and dogs and cats prior to sale by pet stores1. For all of the reasons articulated here, the ASPCA does not support laws that mandate spay/neuter of owned animals that come to shelters as strays as a prerequisite of returning them to their owners. However, provisions that incentivize spay/ neuter in these situations can be an effective strategy that does not create unintended negative consequences, such as preventing low income owners from reclaiming pets due to inability to pay applicable fees. For example, localities and shelters may consider waiving redemption fees if owners opt to spay or neuter their pets (at no or low cost) to incentivize spay/neuter, ensure it is not cost prohibitive to pet owners, and reunite more pets with their families.
In order to assure the efficacy of any spay/neuter program designed to reduce shelter intake and euthanasia, the ASPCA believes that each community must conduct credible research into the particular causes of relinquishment and abandonment and the sources of animals in its shelters, including the barriers to spay/neuter services that are faced by those populations contributing disproportionately to the problem. Each community must address these issues with a tailored, multifaceted approach as described below:
1) The community should have in place an adequately funded, readily accessible, safe, efficient, affordable spay/neuter program.
2) Community research should identify the particular segments of the population that are contributing disproportionately to shelter intake and euthanasia, and the community should produce programs that are targeted to those populations.
3) The community should strive to maximize the accessibility of spay/neuter services and provide compelling incentives to have the surgery performed.
4) The spay/neuter program should be developed with the guidance of veterinary professionals who are committed to delivering high quality spay/neuter services to all patients (Looney et al., 2008).
5) The program must adequately address the contribution that feral and stray animals make to overpopulation.
6) The program must be adequately supported in terms of financing, staffing and infrastructure.
7) The efficacy of all aspects of the program must be monitored and revisions made as necessary to achieve its goals.
In summary, the ASPCA recognizes that sterilization is currently the best method to reduce companion animal overpopulation and therefore to reduce shelter intake and euthanasia. The most important step a humane community can take to decrease companion animal overpopulation is to make a safe, effective, voluntary spay/neuter program available and readily accessible to the community, and create programs and incentives targeted to the populations known to be contributing disproportionately to shelter intake and euthanasia.
1 Dogs and cats in the custody of pet stores, like those found at shelters, are often of unknown origin and therefore their genetic, behavioral and medical histories are uncertain. For these populations of animals- not yet privately owned as pets, and of unclear background - spay/neuter is an important tool to ensure that genetic and medical problems are not unwittingly passed on to offspring, which may then contribute to pet overpopulation, shelter intake and animal control costs.
American Humane Association 2013. A three phase retention study. Phase II: descriptive study of post-adoption retention in six shelters in three US cities http://www.americanhumane.org/petsmart-keeping-pets-phase-ii.pdf 
Chu, K., Anderson, W.M., Reiser, M.Y. 2009. “Population characteristics and neuter status of cats living in households in the U.S.” Journal of the American Veterinary Medical Association, 234, 1023-1030.
Clancy, E. A., Rowan, A. N., 2003. “Companion animal demographics in the United States: A historical perspective.” In: Salem, D. J. & Rowan, A. N. (Eds.), State of the Animals II: 2003. Humane Society Press, Washington, DC, pp. 9-26.
The Foundation for Interdisciplinary Research and Education Promoting Animal Welfare (FIREPAW). 2004. Cross-program statistical analysis of Maddie's Fund programs, Williamstown, MA.
Frank, J., 2001. Executive summary of research results for: the economics, ethics, and ecology of companion animal overpopulation and a mathematical model for evaluation of the effectiveness of policy alternatives. Houston, TX: The Foundation for Interdisciplinary Research and Education Promoting Animal Welfare.
Handy, G., 2002. Animal Control Management: A Guide for Local Governments. International City/County Management Association, Washington, D.C.
Irwin, P. G., 2001. “Overview: The state of animals in 2001.” In: Salem, D. J. & Rowan, A. N. (Ed.), The State of the Animals 2001. Humane Society Press, Washington, DC, pp. 1-19.
Levy, J. K., Gale, D. W., Gale, L. A., 2003. “Evaluation of the effect of a long-term trap-neuterreturn and adoption program on a free-roaming cat population.” Journal of the American Veterinary Association 222, 42-46.
Lord, L.K., Wittum, T.E., Ferketich, A.K., Funk, J.A., Rajala-Schultz, P., Kauffman, R.M., 2006. “Demographic trends for animal care and control agencies in Ohio from 1996 to 2004.” Journal of the American Veterinary Medical Association, 229, 48-54.
Marsh, P., 2008. Analysis using data from New Jersey Department of Health and Senior Services (1998) and the California Department of Health Services (1995).
Miller, G., Slater, M., Weiss, E.. Effects of a geographically targeted intervention and creative outreach to reduce shelter intake in Portland, Oregon. Animal Sciences (2014) .
National Council on Pet Population Study and Policy, 2001. “Exploring the surplus cat and dog problem: Highlights of five research publications regarding relinquishment of pets.” New London, MN. Online at petpopulation.org.
Natoli, E., Maraglioano, L., Cariola, G., Faini, A., Bonanni, R., Cafazzo, S., Fantini, C., 2006. “Management of feral domestic cats in the urban environment of Rome (Italy).” Preventative Veterinary Medicine 77, 180-185.
Office of Legislative Oversight, OLO Report 97-3: An evaluation of Bill 54-91, Revisions to the county's animal control law. June 24, 1997. Montgomery County, MD.
Patronek, G. J., Lawrence, T. G., Glickman, T., Beck, A. M., McCabe, G. P., Ecker, C., 1996. “Risk factors for relinquishment of cats to an animal shelter.” Journal of the American Veterinary Medical Association 209, 582-588.
Patronek, G. J., Lawrence, T. G., Glickman, T., Beck, A. M., McCabe, G. P., Ecker, C., 1996. “Risk factors for relinquishment of dogs to an animal shelter.” Journal of the American Veterinary Medical Association 209, 572-581.
Patronek, G. J., Beck, A. M., Glickman, T., 1997. “Dynamics of dog and cat populations in a community.” Journal of the American Veterinary Medical Association 210, 637-642.
Ralston Purina, 2000. The state of the American pet: A study among pet owners.
Patronek, G.J. 2010. Mapping and measuring disparities in welfare for cats across neighborhoods in a large US city. American Journal of Veterinary Research 71(2), 161-168.
Secovich, S. J., 2003. “Case study: companion animal over-population programs in New Jersey, New Hampshire, and Maine and a new program for Maine.” Master's thesis, Public Policy and Management. University of Southern Maine.
Weiss, E., Slater, S., Garrison, L., Drain, N., Dolan, E., Scarlett, J.M., Zawistowski, S. (2014). Large dog relinquishment at two municipal facilities in NY and DC: Indentifying targets for intervention. Animals.
Zawistowski, S., Morris, J., Salman, M. D., Ruch-Gallie, R., 1998. “Population dynamics, overpopulation, and the welfare of companion animals: new insights on old and new data.”
Journal of Applied Animal Welfare Science 1, 193-206.