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As a colleague of mine once said, “a spay  is a procedure routinely performed, but it is not a routine procedure.” In the U.S., “spay” refers to the surgical removal of the ovaries and uterus. In Europe, however, removal of just the ovaries (ovariectomy) appears to be the most popular sterilization technique. Why are my European colleagues doing things differently, and is there evidence to suggest that they’re right? Is it possible to achieve the same surgical result using a less-complicated, less-involved procedure?
It’s been proven that an ovariectomy, which can be done via laparoscopy (or “keyhole” surgery), requires a smaller incision. Still, to date, no one has proven that removing both the uterus and the ovaries is more painful than taking just the ovaries, and no one has compared complication rates between the two surgical techniques.
However, other aspects have been assessed. In the Journal of the American Veterinary Medical Association , Michael DeTora, DVM, and Robert J. McCarthy, DVM, MS, DACVS, examined the two approaches.* Judging by their report, removing only the main hormone producers — the ovaries — has a lot going for it. Here are a few of their leading points.
One of the big benefits to spaying is the decreased incidence of mammary gland tumors, the most common tumor in female dogs. Sterilize before the first heat and your dog is 200 times less likely to develop breast cancer when compared to a sexually intact dog. Taking or leaving the uterus will not change this risk; rather, the benefit comes from removing the ovaries and their sex hormones.
It has been argued that there are two important reasons to remove the uterus. The first is the risk of developing pyometra, a uterine infection. Typically, pyometra occurs in dogs who have not been spayed and is attributed to the long-term influence of sex hormones, particularly progesterone, produced by the ovaries. In a study of 135 dogs, 66 had a regular spay and 69 had only the ovaries removed. There were no episodes of pyometra in either group up to 11 years after the surgery. In other words, leaving the uterus does not mean your dog will get a uterine infection. Remove the ovaries and you remove the source of progesterone, which means that pyometra cannot occur.
The second concerns the risk of leaving a redundant organ behind, potentially exposing the dog to a future uterine tumor. This appears reasonable until you consider that uterine tumors are extremely rare. In one study, just 11 of nearly 35,000 female dogs had a tumor of the uterus, and only one of these was cancerous. Benign uterine tumors are slow growing, don’t spread to other organs and are easily cured with surgery. The chance of your dog succumbing to uterine cancer is a lot slimmer than your lifetime risk of being killed in a car crash.
This leaves urinary incontinence, one of the most frustrating side effects of spaying. Reportedly, as many as one in five sterilized female dogs will have a tendency to dribble urine after surgery. Exactly why this happens is poorly understood, but the presence or absence of the uterus appears to make no difference.
As a veterinarian, one of my most important roles is to help owners make informed health-care decisions for their companion animals. Evidence-based medicine suggests that there is no recognized disadvantage to taking just the ovaries and leaving the uterus behind. Though inertia is always the biggest barrier to change, I may have a chance to influence the choice when asked the time-honored question, “What would you do if this were your dog?”
“Easy. Take the ovaries. Leave the uterus.”
Illustration by Marian Trotter
*DeTora, Michael, and Robert J. McCarthy. 2011. Ovariohysterectomy versus ovariectomy for elective sterilization of female dogs and cats: is removal of the uterus necessary? JAVMA. 239 (11): 1409–1412.