Feral Cat Control: TVHR Better than TNR

TVHR is more effective than TNR, a study concludes.

This is an interesting study that looks at a modified version of Trap-Neuter-Return (TNR) to make it more effective. The good thing is that the study takes TNR seriously as a way to manage feral cat colonies. The study indirectly validates the concept of TNR, which to sterilise the cats and leave them where they are. A humane process. Note: the study1 was a computer simulation. The objective is to carry it out in real life.

So what is TVHR and how does it differ from TNR?


TNR is well known but it helps to spell out the process. TNR can be called: Trap-Test-Vaccinate-Alter-Release (TTVAR) – “alter” means to neuter (male) or spay (female). The neutering bit of TNR is:

  • male: neutering: testicles removed – castration
  • female: spaying: removal of the uterus and ovaries


The letters stand for Trap-Vasectomies or Hysterectomies-Release

  • male: a vasectomy: the tube that carries the sperm is cut
  • female: hysterectomy: this is the same as spaying, removal of ovaries and uterus.

The difference between TNR and TVHR is that the male cat is sterilised by castration for TNR and has “the snip” for TVHR.

How can this slight difference make a bit difference in the management of feral cats?

Firstly, the research indicates the following:

ProcessPercentage of cats undergoing processEffect after 11 years
TVHR35% of catsPopulation of colony would disappear
TNR82% of catsPopulation of colony would disappear

Why is this? Apparently there are two reasons:

  1. Feral cat colonies – a group of cats – are controlled by a dominant male. If this cat undergoes a vasectomy he retains his sexual hormones and sex drive (as opposed to the castrated cat). He, therefore mates with the females but produces no kittens. If he had been castrated instead he would lose his sex drive and another dominant, breeding, male feral cat would take over the dominant position and seek out females, creating kittens.
  2. Also, an intact (non-spayed) female who has mated with a vasectomised male undergoes a 45-day period of pseudo-pregnancy, which is a further barrier to reproduction.

Well, there it is. This is not a magic formula but the study does promote the humane concept of trapping and sterilising feral cats as opposed to simply killing them.

The one downside of TVHR is that the males behave as if they are breeding cats so their behavior is more intrusive for people living in the location of the colony.

Ref: (1) as reported on the website news.nationalgeographic.com (I don’t have a link to the original study, sorry).

Please search using the search box at the top of the site. You are bound to find what you are looking for.

Useful tag. Click to see the articles: Cat behavior

11 thoughts on “Feral Cat Control: TVHR Better than TNR”

  1. Christine, Ontario

    Please see expert analysis of this TVHR study and it’s implications, by Peter Wolf of Vox Felina and Best Friends Animal Society:

    Reductio ad absurdum

    “Results of a new computer model suggest that sterilization via vasectomy and hysterectomy is more effective than traditional spay/neuter at reducing the population of community cats. But the work raises several questions about the model’s validity—and more troubling ones about its implications for animal welfare.”

    – see http://www.voxfelina.com/2013/08/tufts-researchtrap-vasectomy-hysterectomy-release/

    “JAVMA Letter: A Trojan Horse”
    – All Dollars, No Sense


  2. Christine, Ontario

    Several nuisance behaviours of intact cats are noted by Cats Protection in this pdf. Other than population control, TVHR would not address these issues. I think CP forgot to mention that female cats can also spray urine when they’re in heat, though it’s not nearly as pungent as tomcat urine and so less noticeable outside. Cat owners may be surprised if they’re not aware that this can be normal behaviour of intact female cats.


    I agree with more enlightened cat adoption groups, that cats with FIV deserve to live. We need to neuter, not simply do vasectomies, if we are going to help stop cats from fighting and getting infections from bite wounds. Several vets and groups still don’t even bother trying to adopt out these deserving cats who can live just as long as FIV negative cats.

    Photo of Bud from a non-commercial info resource page on FIV, in Bud’s memory- http://www.FIVtherapy.com
    Credit – the website’s author.

    1. Hi Christine. Thanks for sharing. For the record your links are tagged with “nofollow” which stops any PR benefit being gained. I have to do this to stop spam which is endemic.

  3. Christine, Ontario

    Since this is an issue our city committee is dealing with, I looked at this carefully when it came out. The negatives appear to greatly outweigh any potential positives, however. Lowest initial costs aren’t always the biggest incentive to drive programs.

    The fact that spayed and neutered cats change their behaviour is a major advantage and great selling point of TNR. The cats no longer fight or engage in mating, so they are healthier and have much less nuisance behaviour (less fighting so less disease transmission, females don’t end up with pyometra, cats spend more time grooming, waste less energy patrolling…). Any new cats joining a managed colony also have to be caught and altered, or altered and adopted out if tame.

    I believe TVHR is less humane and has many disadvantages so I would actively discourage my city and local groups from participating in TVHR if it was proposed. Since my city likes fewer nuisance complaints and local groups agree with the reasons in my position, I don’t see any chance of this catching on.

    With the funding of subsidised spay/neuter clinics helping with TNR, available grants, and better organization and fundraising, the cost of TNR has come down as funding has increased.

    If other community programs are also put in place, like subsidised and free spay/neuter for pet cats, assistance with pet retention, rehoming assistance, increased ID incentives (low cost microchipping, pet rewards ID program), and lost cat recovery, the numbers of intact cats who end up outside will continue to decrease.

    Photo: TVHR would not prevent this. This young cat would have died a very painful, preventable death if she hadn’t had surgery.
    “Pyometra – dripping pus every where non-stop.” Pyometra in a one-year-old cat, as posted on http://www.sinpets.com/F6/20120247z-plasty-pyometra-cat-singapore_ToaPayohVets.htm

    1. In your previous comments (which due to time constraints I skimmed) I get the impression that you don’t believe legislation is the answer to dealing with less than adequate cat ownership but education is the solution. If that is true I disagree because although education is the answer, some people need to be forced to change. Only enforced laws can achieve that. TNR is good but the local authorities are slow to adopt it. There are still many detractors – people who dislike cats and who want the cats killed and irresponsible cat owners punished. TNR leaves cats on the street. It is long term. People don’t see results.

  4. Sorry typo.com!!! Should read I knew that male cats with their testicles completely in tact are better able to protect themselves, being known as SCRAPPERS (fighters)

  5. This is really interesting as I had never considered this option. I have often wondered about just the norm where the testicles are removed where feral colonies are concerned as I knew it stopped the desire to breed. I knew that male cats with their testicles completely in tact are better able to protect themselves, being known as acrappers and I often wondered how the castrated ones fared going back into a colony with intact males. Did they get picked on? did they get hurt or chased away? Does anyone know?

    The actual vasectomy option seems much more natural as the males would behave as they did before they left thus less disruption for the colony as a whole. It just seems the better option in ferals however I would have thought less so for domestic cats as they may still be inclined to spray, go after females, fight and be less homely etc.

  6. This is very interesting as I have observed feral colony hierarchy and noticed how once neutered the dominant male often changes, one colony has a very dominant male who even fights and chases foxes that come anywhere near and bullies some other neutered males but on occasion when a stray un neutered tom comes by he stays well out of its way.

  7. As you have pretty much said, this TVHR would be ideal for colonies in remote areas where humans rarely go.

    I think the obstacle would be that it is much faster/easier to burn off testes as opposed to performing vasectomies. As it is, it’s a struggle here to get vets to just neuter ferals at a reasonable price. I don’t know what a vasectomy fee would be.

    I have 3 colonies and have kept 1 of the dominant males intact for the reason of keeping him hormonal. His colony is closest to me and I felt another male may intrude. The females are spayed but an occasional female newbie will appear. Even when I have newbies spayed, he doesn’t wander at all. But, TVHR would be perfect for him.

    1. Nice point Dee, the cost must be a barrier. People don’t want to spend money on feral cats. They are not a high enough priority it seems to me. I particularly like this story because whatever happens it supports humane management of feral cats in one form or another.

      It seems that what you do is much in tune with this study.

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