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Hormone-Protective Sterilization Explained

Having your pet “fixed” used to be a yes or no question, but recent medical research is shining a new light on this topic and offering us new insights about the role of hormones in animal health. There are new alternatives to traditional spay/neuter surgeries.

Research conducted over the last 20 years has examined the impact on canine health of traditional spay/neuter surgery, in which the hormone-producing gonads (ovaries/testes) are removed. As a result, a more nuanced understanding has emerged of the role that sex hormones (gonadocorticoids) play in a dog’s overall lifetime health. Some studies have traced disease emergence in specific breeds; others have taken an epidemiological approach, starting from the disease data and analyzing relationship to fertility. The research suggests that the presence of sex hormones produced in the gonads plays a protective role against many disease conditions, including some cancers, possibly because they are involved in regulating another sex hormone, LH, which is produced by the pituitary gland. For this reason, some vets are now offering specialized sterilization surgeries that preserve the gonads while preventing pregnancy.

Ovary-Sparing Spay (OSS)

An ovary-sparing spay (hysterectomy) involves removal of the uterus but leaves the ovaries intact to produce estrogens and progesterone.  Although tubal ligation would produce the same effect, it leaves dogs open to pyometras (infection of the uterus) and bleeding during estrus (“heat”), so this is not recommended.  


A canine vasectomy cuts, clamps, or ties off the vas deferens, which, as you may recall from high school health class, is the tube by which sperm are carried from the testes to the urethra.  The dog retains his testicles and testosterone but is not able to impregnate a female. Since the dog is hormonally intact, there may still be behaviors such as mounting, peeing to mark territory, and roaming that are significantly decreased in castrated males. Interestingly, although a hormonally intact male may show more dog-aggression with other males, instances of aggression against people and family pets seem to be less prevalent than in castrated dogs. In fact, there is evidence to suggest that removal of the testes might actually increase fearfulness and fear-based aggression in dogs.

Which is Best?

Each pet’s health is unique and deserves individual consideration that takes into account her breed, lifestyle, and medical history. And, of course, our own human lives are complex and variable. Discuss your thoughts and preferences with your veterinarian, who can provide you with information about timing, cost and other factors that will help you decide which option is best for your friend.

Ashley McCaughan, D.V.M., is the owner and founder of Marina Village Veterinary in Alameda, It is Alameda’s first holistic veterinary hospital and opened in February 2018. McCaughan is a graduate from Cornell University School of Veterinary Medicine and works with dogs, cats, pocket pets, rabbits, horses, and other animals. She practices veterinary acupuncture and is also certified in veterinary chiropractic. She is passionate about multi-modal therapy for pain management, using laser, acupuncture, Chinese herbs, and/or chiropractic treatments, in addition to conventional medicines. McCaughan enjoys hiking, mountain biking in Redwood Regional Park, swimming, and competing in a horseback riding discipline called three day eventing.

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