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The Science and Policy of Contraception… in Cats


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800px-Herd_of_CatsSometimes when I come home from work there is a big orange cat sunning himself on my front porch. He ambles away as soon as he sees me – not a panicked dash, because he’s used to humans, but there is certainly no way I’d ever get close enough to pet him. No one owns this cat, although my next door neighbors sometimes feed him, and he clearly lives in the neighborhood; he and my dogs know each other well from high-volume interactions across the fence.

He is a feral cat, sometimes known as a community cat. He probably lives in a small colony, and indeed there are several other individuals that I have seen around, although this is the only one who likes to sleep on my front step.

This orange cat seems to have a pretty good life, which is often true for cats living in colonies that are managed. This colony, as I’ve said, is at least getting fed regularly. However, his life is liable to be shorter than that of an owned cat, and in fact I have already taken two badly-injured community cats to the local veterinary hospital for euthanasia. (As the neighborhood veterinary student I find that one of my responsibilities is dealing with cats who have been hit by cars or attacked by other animals.)

He is also at risk of disease, such as feline leukemia or feline AIDS, because he has probably never been vaccinated. He is not the only one at risk; his colony may maintain a reservoir of these feline diseases which can then be transmitted into the population of owned cats who are allowed outside to interact with their feral cousins. Moreover, community cats are often sexually intact and certainly contribute to the overwhelming number of kittens that my community sees every spring and summer. And, of course, bird lovers complain of the depredations of community cats on the local wildlife.

Time was, people trapped community cats and euthanized them as a means of population control. This didn’t work as well as you might think, because when a colony of cats was depleted, new cats would move in to take their place. It turns out that maintaining a healthy colony keeps new cats out. In the last decade or so, volunteers and animal shelters have been implementing trap/neuter/return (TNR) programs. Cats are trapped and brought to veterinary clinics, where they are vaccinated and spayed or neutered.  They are returned to their colonies, which are managed by caretakers. In this way, colonies are kept small but healthy.

However, TNR programs are maintained at great expense. Veterinary surgeons are not cheap, and even with volunteer veterinarians, a surgical suite also has to be acquired. Cats have to be trapped on a specific day when a TNR clinic is scheduled, not an easy task itself, transported to the clinic and then transported back. The expense slows down the process, and it’s not clear that we can spay and neuter fast enough to keep up with the population.

A simple medical intervention would be much more efficient than surgery. The ideal chemical contraceptive would be inexpensive to make and easy to administer;  a single treatment would have a long term or even permanent effect; it would have a wide margin of safety for both cats and the environment (you wouldn’t want a dead cat to be full of some toxin that would endanger other animals); and it would have a rapid onset of action. Ideally, it would not just prevent litters, but would also reduce the nuisance behaviors associated with breeding, because cats having sex are extremely noisy. The contraceptive should be widely effective, although studies suggest that it only needs to affect 70-80% of female cats in order to achieve population reduction.

There are some possibilities already being studied. Both are vaccines – it’s an amusing idea to vaccinate against pregnancy, but of course vaccines do have a long term effect, so they’re logical choices for this situation. One vaccination target is the zona pellucida. This is the coating around the egg which allows in one, and only one, sperm; vaccinated animals produce antibodies which attack the ZP and therefore inactivate the egg. The nice thing about ZP vaccination is that is is highly species-specific – the ZP is, in fact, part of the mechanism that keeps species from being able to interbreed with each other. Unfortunately, the ZP vaccine which is currently available was not developed specifically against cat ZP, and does not work well in cats. A cat-specific ZP has also been tested but, surprisingly, is not highly effective either. Perhaps more research will sort the problem out, but for now this is not a viable alternative. Additionally, as you might guess from the mechanism, ZP vaccination doesn’t affect mating behaviors even when it works; it only affects conception. So cats will still yowl during sex after ZP vaccination.

A more promising alternative is vaccination against GnRH, the master hormone of the sex hormones. Through minion hormones, GnRH controls production of sperm and ovulation of eggs. Unlike the ZP vaccine, the GnRH vaccine reduces both pregnancy and mating behaviors. Its effectiveness is somewhat unpredictable, so some vaccinated animals keep right on getting pregnant. Its length of effectiveness is also somewhat variable, but can last up to several years in some studies. Although your housecat might live into its late teens, several years of birth control are probably sufficient in shorter-lived community cats.

A commerical GnRH vaccine, GonaCon, is approved in cervids and has been successfully used in white-tailed deer. It has been tested in cats in laboratory settings, but not in the field. The idea is enticing: volunteers could trap cats, then vaccinate them with GonaCon and the usual array of anti-disease vaccines right in the trap, then release them, never having had to bring them in to a veterinary clinic. Efficiency would be hugely increased. Hopefully initial trials would show that GonaCon is effective at population reduction in cats, something that hasn’t yet been proven.

Real life is never so simple, of course. I talked about contraceptive vaccination with a few vet techs at an animal shelter recently. They loved the idea, but pointed out that in our state, once you are providing any medical care for a cat, such as contraception, you have to make sure they are vaccinated for rabies, which legally requires the presence of a veterinarian. Once you have to bring in a vet, of course, the expense starts going up again. We batted around some ideas – maybe you could distribute an oral form of a vaccine in bait form, and get around the rabies vaccination requirement by dint of never actually touching the cat. In this case, the ZP vaccine might be better, as it is more species-specific and presumably could be eaten by other species without effect, but of course the ZP vaccine requires more work before it will be effective in cats.

So chemical contraceptives for community cats aren’t quite ready for prime time, but there are some promising candidates. My suspicion is that the biggest problem is simply willingness on the part of society to commit the resources necessary to develop a workable solution. Cat rescuers and animal shelters, both with notorious money problems, can’t possibly represent attractive markets to drug companies. Who will fund the necessary research and the advocacy for policy changes that are necessary? You can stay up to date with news as the story unfolds at the Alliance for Contraception in Cats and Dogs (http://www.acc-d.org). You can even donate to them. Community cats may be our responsibility, as domesticated animals gone feral, or they may not be, but either way they affect us and the animals we live with. Efficient and humane management of their populations benefits both them and us.

References:

* Julie K. Levy. Contraceptive Vaccines for the Humane Control of Community Cat Populations. American Journal of Reproductive Immunology, Special Issue: Special Issue on Contraceptive Vaccines, Volume 66, Issue 1, July 2011

* Julie K. Levy, JohnA. Friary, et al. Long-term fertility control in female cats with GonaCon(TM), a GnRH immunocontraceptive Original Research Article Theriogenology, Volume 76, Issue 8, November 2011, Pages 1517-1525.

* Alliance for Contraception in Cats and Dogs, http://www.acc-d.org

The Dog Zombie About the Author: The Dog Zombie studies dog brains by pursuing DVM (veterinary medicine) and MS degrees. She is currently in her fourth year of the DVM degree, having completed her research year. Her interests include neurobiology, neuroendocrinology, ethology, animal behavior, canid domestication, shelter medicine, animal welfare, veterinary ethics, open access publishing, and the philosophy of science.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 8 Comments

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  1. 1. hanmeng 2:03 pm 05/5/2012

    This research could also be useful in learning how to control problematic human communities. Like so:

    “This human seems to have a pretty good life, which is often true for humans living in colonies that are managed. This colony, as I’ve said, is at least getting fed regularly. However, his life is liable to be shorter than that of a properly governed human, and in fact I have already taken two badly-injured community humans the local medical hospital for euthanasia. (As the neighborhood medical student I find that one of my responsibilities is dealing with humans who have been hit by cars or attacked by other humans.) He is also at risk of disease, such as leukemia or AIDS, because he has probably never been vaccinated. He is not the only one at risk; his colony may maintain a reservoir of these diseases which can then be transmitted into the population of properly governed humans who are allowed outside to interact with their feral cousins. Moreover, community humans are often sexually intact and certainly contribute to the overwhelming number of children that my community sees every spring and summer. And, of course, nature lovers complain of the depredations of community humans on the local environment.”

    Link to this
  2. 2. BrianSchmidt 1:05 am 05/6/2012

    “It turns out that maintaining a healthy colony keeps new cats out.”

    Not sure if I believe this – got a link?

    If it is at all correct, I suspect it’s the amount of feeding that controls the colony size, i.e. cats get aggressive if there’s not enough food and the weakest cats, probably the new ones until a current one becomes too old, get pushed away. The cats that get pushed away don’t stop existing, of course. All that happens is an allegedly small healthy feral colony is an intense concentration of cats.

    If you want fewer feral cats then stop feeding them. Contraception may be of some help too, but it has to reach the wide-ranging cats, not just the ones that are currently dominant at the colony.

    Link to this
  3. 3. dogzombie 12:12 pm 05/6/2012

    Brian — good call; with my statement about immigration of cats I was referring to things I had been told, but had not sought references for. I did some reference hunting this morning.

    * “Evaluation of euthanasia and trap–neuter–return (TNR) programs in managing free-roaming cat populations”
    (http://dx.doi.org/10.1071/WR08018) states: “Population decreases were comparable among euthanasia, TNR and a 50 : 50 combination for all treatment rates when the immigration rate was 0%; however, they were higher for euthanasia at 25% and 50% maximum immigration rates. Euthanasia required higher treatment effort than TNR. Our results indicate that immigration must be prevented and high (>50%) treatment rates implemented to reduce free-roaming cat populations.” So this study does implicate immigration, but does not find TNR to be more successful than culling.

    * “Evaluation of the effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population” (doi: 10.2460/javma.2003.222.42) states:
    “Trapping began in 1991; however, a complete census of cats was not completed until 1996, at which time 68 cats resided on site. At completion of the study in 2002, the population had decreased by 66%, from 68 to 23 cats (of which 22 were feral). No kittens were observed on site after 1995, but additional stray or abandoned cats continued to become resident. New arrivals were neutered or adopted before they could reproduce.” So this study finds immigration to continue with an established, managed colony.

    TNR vs culling is certainly a hot topic in the animal shelter community and the wildlife community. My intention in this post was to discuss medical ways of making TNR more efficient, not to address its efficiency vs culling; I should have written the post most more carefully to avoid assumptions in that area.

    I will agree that TNR as currently implemented is ineffective in many areas. My belief is that we should try to find ways to make it more effective, but of course others’ opinions on appropriate policy choices will differ.

    Link to this
  4. 4. Medikus 11:35 am 05/7/2012

    I work in the company which sells contraceptive vaccination(http://www.shopmedvet.com/), but it not is a popular product.

    Link to this
  5. 5. karen@ACC&D 4:09 pm 05/10/2012

    Medikus, what product is it that your company sells? Is it one of the hormonal contraceptives? I was unable to find any contraceptive on your site.

    Thank you,
    Karen at the Alliance for Contraception in Cats & Dogs

    Link to this
  6. 6. poihths 5:27 pm 05/17/2012

    People who want to deal with feral cats would be well advised to be sure that the animal is indeed feral. One of our cats, for example, is an outdoor cat who will not tolerate a collar; the guy has gotten rid of more collars than I care to think about. He also roams widely in the two natural areas near us. It would be very easy to think he was feral until you find out he has a chip.

    Link to this
  7. 7. Mazelle 2:19 am 01/2/2013

    Are you KIDDING me? You claim to be a veterinary student, correct? Are you not then aware that female cats allowed to cycle but not allowed to become pregnant (ESPECIALLY if they are in less than sanitary conditions and/or having intercourse)tend to acquire a severe and fatal infection of the uterus (Pyometra) that when left untreated usually results in a very painful death?

    How any veterinary professional could recommend a birth control method for female cats without taking this into consideration is negligent at best and malpractice at worst. I’ve seen queens with this condition, it’s horrible. You CAN NOT leave female cats to cycle.

    What ever happened to the ‘depo-provera’ shots? They work to suppress ovulation for 3months at a time- can that be extended? Humans have a norplant method, 5 years of birth control is a near lifetime solution in a feral cat.

    Imagine the poor young female kitties, bellies swollen like they’re pregnant, hiding in pain, that you’d be taking in to be needlessly euthanised if this proceure became commonplace!

    There are better solutions. We MUST take side effects into consideration!!

    Sandra Cowdrick

    Link to this
  8. 8. Mazelle 2:26 am 01/2/2013

    Please know, however, I understand how important this subject is, and am very appreciative of you and others for addressing it, however, when you submit articles for publication in magazines such as this many who read your words take them as gospel, that is one heck of a responsibility.

    Link to this

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