Research about spay and neuter for dogs

The latest research suggests that spay and neuter procedures are often done too early in life, and may cause health issues later on.

Most people would say that dog (and cat) overpopulation is a serious issue, and that all companion animals should be spayed or neutered. In North America, spay and neuter surgeries are routinely performed in most animal clinics. But in Europe, a much smaller percentage of animals are spayed or neutered.

What’s the real truth about the benefits and risks of these surgeries? And does the increasingly frequent practice of early spay and neuter amplify the risks? Recent studies have uncovered some interesting results.

Are dogs being spayed/neutered too young?

Conventional veterinary wisdom recommends that dogs be spayed or neutered between six and nine months of age, and preferably before the first estrus cycle in females. But this recommendation is based less on scientific fact and more on practicalities; younger puppies can be riskier candidates for anesthesia, though current drugs and methods are safer than they used to be. In other words, there is no scientific evidence for spaying or neutering at an early age.

Opponents of early spay/neuter (especially younger than five-and- a-half months) contend that a variety of orthopedic and other issues can result from these procedures. Deprivation of sexual hormones and development through puberty may create long-lasting physical and psychological harm.

Other potential risks

Further recent studies have been finding some unpleasant effects stemming from spay/neuter procedures, especially when they are done before one year of age.

• Higher risk of certain types of cancer – Some studies are finding that spayed and neutered animals may have a higher risk of certain types of cancer, such as prostatic adenocarcinoma, lymphoma, transitional cell carcinoma (the risk is two to four times higher in spayed females), and hemagiosarcoma. In the case of prostate cancer, researchers hypothesize that hormones may play a role in slowing the progression of the disease.

• Orthopedic issues – The physes, or growth plates, of long bones generally close at one year of age. Spay and neuter procedures performed before this age delay the process, resulting in increased lengthening of long bones. The clinical signifi cance of this is unknown, but opponents of early spay/ neuter claim that this abnormal bone length alters the angle of the joints, making injury and arthritis more likely.

One study done on golden retrievers at the University of California, Davis, found that the risk of hip dysplasia doubled, and the disease occurred at a younger age in early-neutered dogs. The study also found an increased incidence of cranial cruciate ligament (CCL) injuries. While the findings of this study are compelling, early spay/neuter proponents point out that the conclusions are only applicable to one breed, and those who have concerns about their animals’ development can wait until after physeal closure occurs to spay or neuter.

• Obesity – It is well documented that spay and neuter procedures result in slower metabolism. It has also been observed that spayed females exhibit increased appetite and food intake. The role that sex hormones play in metabolism is not well understood, but this particular risk can be controlled with appropriate diet and adequate exercise.

• Urinary issues – Spayed females have a higher risk of developing urinary tract infections and urethral sphincter mechanism incompetence (incontinence). The risk of incontinence may be even greater if the spay procedure is done before three months of age. The exact cause is unclear, but current research is looking at the possible role of a hormone called gonadotropin.

Spay/neuter also offers benefits

Although research is showing that spay/neuter procedures can have risks attached to them whatever the dog’s age, they also offer some long-term benefits.

1. Reduce behavioral problems

Spay and neuter procedures can improve or eliminate problem behaviors, such as mounting, marking and aggression. However, surgery does not help with non-sexual behavior problems, such as separation anxiety or food aggression.

2. Prevent some cancers

These procedures can prevent some types of cancer, such as mammary gland tumors (50% are malignant in dogs), testicular tumors (the second most common tumor type in dogs), ovarian and uterine tumors.

3. Additional benefits

a) Neutering males decreases the incidence of benign prostatic hyperplasia and prostatitis, and may also cut down on risky behaviors, such as the tendency to wander and fight.

b) Studies have found that spayed and neutered dogs enjoy longer lifespans, though the exact reason remains unclear. It may simply be related to better husbandry – in other words, people who get their animals spayed or neutered take better overall care of their companions.

So what should you do?

The latest studies may be uncovering some uncomfortable truths about the risks of spaying and neutering. There are both pros and cons surrounding the procedure. Talk to your veterinarian about your individual pup’s potential risk factors, and/or about spaying or neutering at a later age. For example, if you’re going to compete with your dog in physically demanding sports, you may want to wait until bone growth is complete before having him neutered, to decrease the potential for injury. Of course, until neutering or spaying takes place, you’ll need to carefully monitor your dog to ensure no unplanned pregnancies occur. At the end of the day, whether or not you spay or neuter your dog is a personal choice that depends on your own views, and your dog’s risk factors and lifestyle.


Veterinarian Dr. Erin Mayo graduated from the North Carolina State University College of Veterinary Medicine in 2002. She received her veterinary acupuncture and Chinese herbal certification from the International Veterinary Acupuncture Society, and provides holistic and TCVM services for companion animals in central New Jersey.