Dr. Robert McCarthy is a veterinary surgeon that specializes in orthopedic and soft tissue surgery. Dr. McCarthy received admission to veterinary and medical school but decided to pursue veterinary medicine. Currently, Dr. McCarthy works at the Cummings School of Veterinary Medicine. Dr. McCarthy has a keen interest in feral cat population management and has performed research on the topic; specifically the effects of trap-vasectomy-hysterectomy-release. Releasing sterile felines that retain their sex hormones and associated characteristics may be more effective than trap-neuter-release programs. Dr. McCarthy will be presenting his work at the 2015 Summit for Urban Animal Strategies.
InfoStream (IS): What do you feel are the key issues with feral cat overpopulation?
Dr. Robert McCarthy (RM): Everyone agrees that there are way too many feral cats. There are two divergent camps on how to deal with this problem. Essentially, trap-neuter-release advocates and those that recommend some sort of lethal control method. The problem is that both of these groups believe their respective method would work, if just used enough. Unfortunately, the reproductive potential of cats is incredible, and there is absolutely no evidence that except in very exceptional circumstances either method will succeed. Massive amounts of financial resources have been expended employing these methods with almost no success.
It is time to think outside the box. How much money and manpower needs to be spent before we come to the obvious conclusion that what we are doing simply does not work?
IS: How did this research develop; what interested you about sterilization techniques for feral cats?
RM: I am an avid SCUBA diver and spend as much time as possible diving around tropical islands. On many of these trips, when learning that I was a veterinarian, local residents would complain that feral cats are destroying the indigenous flora and fauna. They would indicate that for many years groups of veterinarians from the US and Canada have come and performed TNR, but there were just as many cats as ever. Essentially, in their minds, there was no question that TNR simply did not work.
I have an interest in wildlife and wildlife management, and it is well accepted that successful reproductive control in the wildlife environment requires maintaining normal reproductive behaviors. Feral cats are essentially wildlife, and it made sense to me that their control should be treated in the same manner.
IS: How was your research performed?
RM: When I returned from a dive trip several years ago I contacted a biologist (J Michael Reed) and a computer engineer (Steve Levine) at Tufts about trying to construct a computer model on the predicted effect of maintaining hormones in a feral cat control program. Essentially we looked at feral cat control by trap-vasectomy-hysterectomy-release. Over several years we hashed out the model, and published the results in the Journal of the American Veterinary Medical Association. The results suggested that feral cat population control is likely to be much more effective if reproductive hormones remain intact.
IS: Why are vasectomies and hysterectomies more effective at reducing the feral cat population?
RM: Trap-Vasectomy-Hysterectomy-Release (TVHR) creates a large group of sterile male and female cats that cannot be differentiated from fertile cats in the population that were unable to be trapped. Dominant males that have been sterilized by vasectomy will still compete for females, use up the female’s receptive time, and fight off fertile males that are attempting to copulate. Females that have been sterilized by hysterectomy will continue to attract males and compete with fertile females for male courting and breeding time. Since neither sex can tell who is fertile and who is not, both sexes spend a large amount of wasted time and energy copulating but not producing offspring.
Female cats are in heat (and therefore sexually receptive) essentially every other week during the entire breeding season. In a typical 8-month breeding season, females will therefore have 16 periods of sexual receptivity, and 16 possible chances to become pregnant. Provided there is an intact male in the population, pregnancy is essentially inevitable. An unusual characteristic of the cat reproductive cycle, however, is that if a female has a sterile copulation (such as with a male that has had a vasectomy) she will not come back into heat for another 8 weeks. Only 4 periods of sexual receptivity (and therefore 4 chances of becoming pregnant) will then be possible during the entire breeding season.
Male cats sterilized by vasectomy may prevent immigration of new intact male cats into the area better than castrated cats.
Adult feral cats sterilized by traditional methods in a TNR program have been shown to live longer, thereby counteracting attempts at population control. In addition, kittens living in a feral cat population have been shown to live longer when the adults are sterilized by traditional methods even if they themselves are not sterilized. Because hormones remain intact, sterilization by vasectomy and hysterectomy will not have the undesired effect of increasing the lifespan of either adults or kittens in the population.
IS: What are the main barriers to implementing these different surgical techniques for feral cats?
RM: Thinking outside the box. The great majority of funding for feral cat control projects comes from individuals, governments, and institutions with preconceived notions of what will work, and vested interest in what they will support. There is extensive and conclusive data that shows none of the methods currently employed is likely to work. The vasectomy/hysterectomy method has to be at least as effective as current methods. Our computer model suggests that it may be much more effective.
IS: Are vasectomies and hysterectomies easier or more difficult for a vet to perform? They are becoming more popular for dogs however many vets will not perform these procedures.
RM: A hysterectomy is about the same difficulty as an ovariohysterectomy for a vet to perform. The main difference is with the castration vs. vasectomy. Vasectomy requires a very small abdominal incision whereas castration does not. This is certainly a bit more difficult, but is still a very easy surgical procedure that can be done with minimal training by any general veterinary practitioner. The question of vasectomy in dogs is really good. There is increasing evidence that sterilization with preservation of hormones may also be very important in pet animals. Veterinarians, like everyone else are trained in a certain way and are slow to change.
IS: Is there anything else you would like us to know?
RM: I think the only thing I would like to stress is that I got into this issue as an unbiased outsider. I am a diver, and simply was told repeatedly by local residents that TNR wasn't working. I researched the issue, found that lethal control is also not effective and came up with an alternative plan. I really didn't have any preconceived notions or goals. I don't have any financial incentive or bias. I simply researched the issue and these were the results. Sterilization with preservation of hormones is likely to be much more effective at reproductive control.
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