TNR and TVHR as methods to control nuisance from feral cats

Ireland, T., & Neilan, R. M. (2016). A spatial agent-based model of feral cats and analysis of population and nuisance controls. Ecological Modelling, 337, 123-136.

Free-roaming feral cats are common in areas of concentrated human habitation, and can pose considerable threats of nuisance and damage to native ecosystems. Trap-neuter-return (TNR) and trap-vasectomy-hysterectomy-return (TVHR) are two humane methods for the reproductive control of feral cat populations. Both TNR and TVHR render a cat infertile, but cats that have undergone TVHR continue to produce hormones that drive mating behaviors. We built a stochastic agent-based computational model for simulating the survival, reproduction, and movement of individual feral cats and the use of TNR and TVHR to modify cats’ reproductive abilities and behaviors. Daily movement of cats between colonies is implemented based on the distance between colonies and landscape properties (e.g. rural, urban). Spatially targeted TNR and TVHR policies are evaluated using two management goals: (1) reduce total population size and (2) reduce nuisance attributed to feral cats. Nuisance includes spraying and noise, both of which are associated with un-neutered males, as well as population abundance. Results indicate that both TNR and TVHR have the potential to greatly reduce population size. Effectiveness of each control depends on the capture rate, number of colonies targeted, size of each colony, and movement of individual cats between colonies. Results show that on average TVHR performs moderately better than TNR at reducing population size, but TNR substantially outperforms TVHR in reducing multiple nuisance measures.

Focusing on specific age classes in spay programs

Lancaster, E. P., Lenhart, S., Ojogbo, E. J., Rekant, S. I., Scott, J. R., Weimer, H., & New Jr, J. C. (2016). Modeling Interventions in the Owned Cat Population to Decrease Numbers, Knox County, TN. Journal of Applied Animal Welfare Science, 1-12.

To find management strategies for controlling the owned cat population in Knox County, TN, the authors formulated a mathematical model using biological properties of such nonhuman animals and spay actions on certain age classes. They constructed this discrete-time model to predict the future owned cat population in this county and to evaluate intervention strategies to surgically sterilize some proportion of the population. Using the predicted population size and the number of surgeries for specific scenarios, they showed that focusing on specific age classes can be an effective feature in spay programs.

Impact of hysterectomy in an urban cat colony

Mendes-de-Almeida, F., Faria, M. C. F., Landau-Remy, G., Branco, A. S., Barata, P., Chame, M., Salim Pereira, M.J. & Labarthe, N., 2006. The Impact of Hysterectomy in an Urban Colony of Domestic Cats (Felis catus Linnaeus, 1758). International Journal of Applied Research in Veterinary Medicine. 4(2): 134–141. 

The easiness with which urban cats form colonies and the exponential growth of these populations are a challenge for all known population control methods. The zoological garden of Rio de Janeiro (RIO- ZOO) has been dealing unsuccessfully with the issue of stray cat populations for more than 10 years. For this reason, it was decided to investigate the structure and composition of the colony of cats populating the RIOZOO and to observe, during 36 months, the impact of hysterectomy of adults, with conservation of the gonads, as a means of population control. Hysterectomy was meant to be performed biennially, though at the beginning of the program, it was performed yearly for 2 consecutive years. The total size of the colony was estimated each year using the capture-mark-recapture tech- nique. During the study's entirety, a total of 96 cats, 80 adults and 16 kittens, were caught. The yearly population estimate of cats showed that between the years 2001 and 2004, the population stopped to grow, strongly tending to decrease. The conservation of the gonads of all animals adding to the fact that no individuals were removed preserved the natural social behavior of the cats living in the colony. Thus, after 2 consecutive years of submitting captured adult females to hysterectomy, planned biennial interventions constitute an animal welfare- friendly, effective model for controlling the urban population of cats that can be proposed to public health authorities as an alternative to the traditional capture and culling in Brazil

Reduction of feral cat colony size following hysterectomy of adult female cats

Mendes-de-Almeida, F., Remy, G. L., Gershony, L. C., Rodrigues, D. P., Chame, M., & Labarthe, N. V. (2011). Reduction of feral cat (Felis catus Linnaeus 1758) colony size following hysterectomy of adult female cats. Journal of feline medicine and surgery, 13(6), 436-440.

The size of urban cat colonies is limited only by the availability of food and shelter; therefore, their population growth challenges all known population control programs. To test a new population control method, a free-roaming feral cat colony at the Zoological Park in the city of Rio de Janeiro was studied, beginning in 2001. The novel method consisted of performing a hysterectomy on all captured female cats over 6 months of age. To estimate the size of the colony and compare population from year to year, a method of capture-mark-release-recapture was used. The aim was to capture as many individuals as possible, including cats of all ages and gender to estimate numbers of cats in all population categories. Results indicated that the feral cat population remained constant from 2001 to 2004. From 2004 to 2008, the hysterectomy program and population estimates were performed every other year (2006 and 2008). The population was estimated to be 40 cats in 2004, 26 in 2006, and 17 cats in 2008. Although pathogens tend to infect more individuals as the population grows older and maintains natural behavior, these results show that free-roaming feral cat colonies could have their population controlled by a biannual program that focuses on hysterectomy of sexually active female cats.

Reply to McCarthy et al. (2013) on methods to control feral cats

Lepczyk, C. A., Conant, S., Duffy, D., Unit, P. C. S., Honolulu, H., Bird, D. M., & Calver, M. (2013). Feral cat management. Zoonoses Public Health, 60, 189-195.

Reply to McCarthy et al. (2013) 

TNR vs. TVHR to control feral cats

McCarthy, R. J., Levine, S. H., & Reed, J. M. (2013). Estimation of effectiveness of three methods of feral cat population control by use of a simulation model. Journal of the American Veterinary Medical Association,243(4), 502-511.

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.



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