Canine Neutering


Question: As a subscriber, I would like to ask Dr. Mike the following questions. Have any medical studies been conducted to evaluate the health benefits of neutering your dog? I have heard repeated claims that neutered pets are healthlier and happier. Beyond the benefits of eliminating the possiblilty of testicular cancer and reproductive drive and perhaps the elimination of some male to male aggressiveness is there any evidence of other health benefits? Also is there any negative health effects associated with the reduced levels of testosterone after neutering? Thanks, Corinne Answer: Corrinne- There have been a few studies evaluating the effects of castration on dogs, usually either concentrating on behavioral effects or effects on prostatic disease. These are the most commonly mentioned benefits, by veterinarians, of castration in dogs: Decreased aggression (supported by studies) Decreased urine marking (supported by studies) Decreased roaming (neither supported nor refuted by studies) Reduction in benign prostrate hypertrophy (supported by studies) Reduction in prostatic infections ( could not find supportive studies) Elimination of testicular cancer (no studies -- obvious conclusion) Rural practitioners add less chance of being hit by cars and shot by angry female dog owners (no studies) These are the most common worries among pet owners: Personality changes such as decrease in "maleness" or courage (not supported or refuted) Weight gain (studies show that a percentage of castrated males gain weight - the exact percentage and rate of weight gain vary from study to study) These are two concerns that dog breeders have that rarely are mentioned by pet owners: Increased risk of prostate cancer (no conclusive studies -- but it is clear that there is no protective effect associated with castration) Increased risk of orthopedic disorders / conformation problems (no studies directly relating castration and orthopedic disorders but studies do show that increased weight gain during growth can cause problems with hip dypslasia, so by combining weight gain and orthopedic studies some risk is likely) To sum this up, I think that it is much harder to make a clear case for the health benefits of castration in male dogs than it is for the health benefits of spaying female dogs, except if you factor in euthanasia due to unwanted activities like urine marking that are often helped by castration. There was a study done which showed a small increase in the risk of prostatic cancer in castrated males but the statistical significance and study size were both small. It does seem clear that castration does not help to prevent prostate cancer, though. It does help in prevention and treatment of benign prostate hypertrophy. This seems like it might not be a big deal, given the "benign" in the name, but when the hypertrophy is significant this disorder is a problem. We do not think that there is much appreciable change in personality in dogs that are castrated, although some owners disagree. In our experience it rarely helps with aggression unless the owners are willing to undertake a behavioral modification program, as well. We do think that it cuts down on roaming, if castration is done before the dog goes off to seek females in the first place, which also cuts down on fight wounds, gunshot wounds and injuries from being hit by cars -- all of which can also be avoided by supervision or containment of male dogs, as well. I think that the risk of orthopedic problems in dogs allowed to gain excessive weight when growing is real. It is important to control weight gain in all growing dogs, but especially in those that are neutered and show an increased tendency towards weight gain. The effect of testosterone reduction on other hormonal systems is not well studied, or at least not in the mainstream publications for general veterinary practitioners. I suspect that this is an area in which more research will be done in the future since more sensitive assays are being developed for measuring canine hormones all the time and because medications are being developed, such as selegiline (Anipryl Rx) which have direct effects on hormonal regulatory mechanisms. While we have not studied this in our practice, I am nearly certain that we could make a good case for neutered pets living longer. But this may be a function of the fact that at the current time there is an emphasis on neutering pets and an general feeling that it is the responsible thing to do --- so the pet owners who are responsible type people feel an obligation to do this and they also take better care of their pets. If you have questions about other health benefits or adverse effects of castration that I missed, please feel free to write again.


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...