Recommendations to spay and neuter pets have been a part of the American cultural landscape for decades. The benefits have been, for the most part, individually and collectively well accepted. But recent research suggests that surgical sterilization may also bring a complicated blend of long-term health risks, in addition to the benefits.
The first study, conducted at the University of California, Davis, found a greater occurrence of hip dysplasia, cranial cruciate ligament tears and two types of cancer (lymphosarcoma and hemangiosarcoma) in golden retrievers, when compared with their intact counterparts. The health risks seems to be greater for dogs spayed or neutered under a year of age. Early neutered males had double the incidence of hip dysplasia. The cancers were 5-8% more likely in both sexes when neutered before 12 months.
The second study, done at the University of Georgia, found that those animals who were spayed or neutered lived longer. It was done on a large number of dogs,at many hospitals.
They found that spaying or neutering was strongly associated with a longer life span and a decreased risk of death from infectious disease and trauma. But there seemed to be an increased risk of death from cancer. The question is whether there are more incidences of cancer, because more dogs are living longer, and thus more susceptible to cancer.
So, thus the news of these two studies has helped to fan the flames of the debate which has raged, on and off, and now on again, for decades. What is a veterinarian like myself to do when questioned about it? And, more importantly, what is the public to think to help them decide what is best for their pet? I think it best to break it down into details.
First, these studies are addressing the timing of neutering, not whether to neuter or not. Also, there are only 2 studies, one of which is in a single breed, the Golden Retriever. I am in no way diminishing the results or their significance, and welcome many more studies on the subject. These studies, I feel, challenge us all to think differently on the subject of if and when to neuter. And, these are dog studies. There are many prior studies on both dogs and cats, obviously leading us to the current recommendations in this country. Neutering rates are different outside of the US. There are advantages and disadvantages of neutering, both before and after sexual maturity. They should be spelled out, as we know them, to help us all make the right decisions, and recommendations. So let’s talk Pros and Cons.
1. In this country, there are many non-medical reasons to consider when deciding to neuter or not neuter our pets. In our culture, dogs and cats are viewed as family members. Dog parks and doggie daycare are modern inventions reflecting both our culture and social trends. Neutered pets tend to do better, or are more welcome in those scenarios.
2. Some behaviors are affected by sex and sex hormone influence. The presence of testosterone has been associated with urine marking with a lifted leg, roaming and some types of mounting. Note that both sexes mount. An old, much referenced study, in 1976, determined the following effects of castration. Roaming decreased by approx. 90%, male-to-male aggression by approx. 75%, urine marking by approx. 60% and mounting by 80%. Note that part of mounting and fighting is learned and may not completely resolve with neutering.
3.Female aggression was harder to connect to aggressive behavior. It seemed to indicate that young, aggressive bitches might be less aggressive if allowed to have one heat cycle prior to spaying.
4. Neutering males and females is usually recommended for aggressive dogs and cats, not because it is therapeutic but because it prevents a heritable behavior component from being passed on to progeny.
5. Common reasons owners decide to neuter male dogs include: the dog marks urine, has enlarged prostate, has had prostatic or testicular cancer, or a working dog is more focused on other dogs’ odors than his job.
6. Clients often decide to spay cats and dogs to avoid the behavioral and physical consequences of heat cycles.
7. Mammary cancer is extremely common in dogs. The tumors are malignant 50% of the time. In countries where dogs are not routinely spayed, the risk may be as high as 53%. Spaying before the first heat decreases the risk to 0.5%, while waiting till the second heat increases the risk to 8%. After the second heat, the risk is 26%.
8. In cats, the patterns are similar, but the tumors are malignant 85-90% of the time.
9. Repeated heat cycles increase the risk of pyometra. Certain breeds are more prone to pyometra, and one study estimated that 25% of intact dogs were at risk . It can be a life threatening condition, typically treated by spaying and administering antibiotics.
10. Prostate disease increases with age, and castration both prevents and treats benign prostatic hyperplasia. Most prostate cancers are diagnosed when advanced and do not improve with neutering, unlike testicular tumors, which are treated by castration.
11. Castration may increase the risk of bladder transitional cell carcinoma and prostate carcinoma, and osteosarcoma. Yet there are strong breed influences in these diseases. Spayed females of certain breeds may have increase risk of hemangiosarcoma.
12. Early neutering increases long bone growth, which could increase hip dysplasia risk.
13. Female shelter puppies spayed prior to 3 months have increased risk of bladder infections and urinary incontinence later in life. If attempts are made to wait until 3 months, the incidence is less. But, it has been shown that these young neutering of shelter pets is preferred if they would not otherwise be neutered. Intact dogs and cats that roam are often killed by cars, etc. And, neutered shelter animals are more easily adopted.
14. Chemical castration is sometimes done, and decreases the risk of incontinence in dogs. With it, cats experience less libido, decreases in mounting and mating behaviors, and spraying. Yet, they eat more, increasing the risk of obesity which is epidemic in cats.
So, overall, the issue is complicated. For the record, I spayed or castrated all of my pets at 6 months of age. Clearly, there is no single right answer for every person or pet. Shelter environments are quite different than households, and the decision should be made after discussing it with your veterinarian. Each dog or cat, with their individual breed concerns, and behavioral issues, lifestyles and medical issues that will and should help dictate the right decision for you.