As trap-neuter-vaccinate-return (TNVR) — or as it’s more commonly called, TNR — is increasingly utilized for the management of unowned, free-roaming cats , critics have raised concerns about the welfare of the cats being returned to where they were trapped [see, for example, 2,3]. These same concerns are often raised when animal shelters implement return-to-field (RTF) programs (sometimes called shelter-neuter-return, or SNR).
The studies summarized here demonstrate that these cats are generally healthy, showing improved health and welfare after being subjected to sterilization and vaccination programs.
What we know about cats after TNR
Because cats involved in TNR or RTF programs are rarely tracked and consistently examined following the return step, detailed information about their health and welfare is relatively scarce. However, some studies (e.g., those conducted on college or university campuses) have provided such long-term data. In addition, studies of large-scale shelter-based programs provide useful information regarding the general health of the cats involved.
Observations on the general health of free-roaming cats
A study of a two-year TNR program (2,366 cats total) in Alachua County, Florida, reported that “euthanasia was performed for 11 (0.5%) debilitated cats” , while a similar study of six three-year, shelter-based TNVR/RTF programs (involving a total of 72,970 cats) found that 0.5% (349 cats) were euthanized for serious health concerns. By comparison, 83% (60,613 cats) were returned to their trapping sites and 15% (10,698 cats) were adopted or transferred to rescue groups for adoption .
A survey of seven TNR organizations across the U.S. found that, overall, 0.4% (range: 0.03–0.7%) of the 103,643 cats for which records were available were euthanized “because of the presence of debilitating conditions, such as neoplasia, chronic inflammatory conditions, trauma, and infectious diseases” observed during routine examinations .
Researchers assessing body condition score (BCS) — based on a 9-point scale ranging from 1 (emaciated) to 5 (ideal) to 9 (grossly obese) — for 63 intact adult cats brought by caregivers to a TNR clinic in Alachua County, Florida, reported a range of 3–7 (medians varied seasonally at 4 or 5). A year following sterilization, median BCS for 14 of the study’s original cats had increased to 6 .
Impact of neutering on cat behavior and welfare
Researchers observing cats in the Israeli city of Rishon LeZion noted higher BCS among both sterilized and intact cats in the area, suggesting that this might be the result of behavior changes among the neutered cats: “Less aggressive behavior may result in a reduction of competitive behavior by neutered cats, which may enable other cats to gain additional access to vital resources” . However, these researchers also documented an overall prevalence of 13.7% of cats with “at least one external sign of illness (any external injury or disability, any skin lesion or emaciation),” noting that this is higher than what has been reported in similar studies from the U.S. and U.K. .
Observations of cats in Auckland, New Zealand, revealed that 64% of both “managed stray” (210 cats total) and “unmanaged stray” cats (253 total) studied received an ideal BCS (compared to 76% of indoor-outdoor pet cats). Scores were also assigned to coat condition, nose and eye discharge, ear crusting, and injuries, with the result that scores for stray cats were comparable to those for pet cats in all categories except coat condition .
Body condition scores for stray cats were comparable to those for pet cats in all categories except coat condition.
In San José, California, a 20% reduction in the number of cats found dead in the city was observed four years after the implementation of an RTF program . Similar results were observed in the aforementioned study of six three-year, shelter-based TNR/RTF programs, though the variation in absolute numbers was considerable . It’s been suggested that these reductions are at least in part attributable to the neutering of male cats, which are then less likely to roam .
Infectious disease risk in outdoor cats
Studies have shown that cats with outdoor access are more likely to acquire parasitic and viral infections compared to cats kept exclusively indoors . Among free-roaming cats, studies show that sterilized cats, and especially those in “managed colonies,” often have infection rates comparable to pet cats with outdoor access.
Studies show that sterilized [free-roaming] cats often have infection rates comparable to pet cats with outdoor access.
One study of 100 “intensively managed” (i.e., vaccinated against the most common feline diseases and rabies, and treated for parasites) unowned free-roaming cats and 76 pet cats (47% of whom had outdoor access) in rural Randolph County, North Carolina, for example, found “similar prevalences of infection with Cryptosporidium, Giardia, and Toxocara cati” between the two groups, while the unowned cats exhibited higher seroprevalences of Bartonella henselae (93% compared to 75%) and Toxoplasma gondii (63% compared to 34%), likely because of “greater exposure to vectors of these organisms” [13,14].
Prevalence of FIV and FeLV
Rates of feline immunodeficiency virus (FIV) infection were comparable (5% and 4%, respectively), while the rate of feline leukemia virus (FeLV) was significantly higher (4%) in unowned cats compared to owned cats (1%) .
Other than zoonotic diseases (e.g., rabies virus, toxoplasmosis), FIV and FeLV are often the infectious diseases of greatest concern to those responsible for the management of free-roaming cats. One study of free-roaming cats in Russellville, Arkansas, revealed infection prevalence rates of 12% and 15% for FIV and FeLV, respectively . Such rates are considerably higher than those typically reported in the literature and are likely a reflection of what the author describes as a “hotspot” for these diseases as well as the cats’ presumably unsterilized status (few details were provided on their sterilization status).
A study of unowned free-roaming cats admitted to TNR programs in Raleigh, North Carolina (733 cats), and Gainesville, Florida (1,143 cats), on the other hand, revealed overall infection rates of 3.5% for FIV and 4.3% for FeLV, “similar to infection rates reported for owned cats” . And the previously mentioned study of Ocean Reef cats reported infection rates of 3.3% and 3.6%, respectively, among the 2,327 cats tested . These results correspond reasonably well with those from large-scale studies examining prevalence rates in U.S. and Canadian cat populations (owned and unowned) [18–20].
Role of sterilization in preventing disease transmission
Although it’s been suggested that higher prevalence rates might be associated with “the size of the feral cat population and the relationship between cat density and patterns of contact among cats” , it’s well known that sexually intact male cats are prone to higher rates of FIV infection and that kittens are more susceptible than adults to FeLV infection [16,21,22]. Sterilization status therefore plays a critical role in the transmission of both diseases.
Average life expectancy of feral and stray cats
Over the course of an 11-year observation period, more than half of the 23 unowned cats living continuously on the University of Central Florida campus (sterilized and managed as part of a TNR program) were estimated to be 6.8 years old or older . Similarly, a study of a TNR program on the University of New South Wales campus (Sydney, Australia) estimated the age of nine long-term resident cats (13% of the original cohort of 69) to be at least 10 years old . The average mortality rate observed is, the authors note, comparable to that of pets cats in England, who, according to one study , have an average lifespan of 14 years .
A 23-year study of 2,529 cats sterilized and monitored at the Ocean Reef Club community (Key Largo, Florida) estimated the mean age of cats who had disappeared or were found dead to be 59 months while the mean age of cats euthanized due to health concerns was estimated to be 82 months .
Short-term studies (1–2 years in duration) have also been used to estimate the life expectancy of free-roaming cats. A 19-month study of 39 radio-collared cats living in the “natural habitat fragments in the Chicago metropolitan area,” for example, resulted in an estimated life expectancy of 2.0–4.5 years . A similar study of 27 unowned cats conducted over 14 months in a mix of rural and urban, residential, industrial, and agricultural land in central Illinois estimated life expectancy to be 1.6 years .
Another 14-month study of 44 radio-collared cats (30 feral, 14 semi-feral) in the “small, suburban community” of Caldwell, Texas, resulted in life expectancy estimates of 1.8 years for unsterilized male feral cats and 7.8 years for female feral cats (one of eight was sterilized). By comparison, the life expectancy for semi-feral cats (male and female combined, and so designated if researchers “observed them being fed by a resident”) was estimated to be 9.5 years 
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