A reader of our Healthy and Happy Dog website contacted us, asking for more information about pyometra. Her vet was recommending ovariohysterectomy (traditional spay which removes the ovaries and uterus) rather than tubal ligation because the risk of pyometra in female dogs who have not been spayed is great. We decided a more in-depth look at the risks of female dogs developing pyometra was in order. For details about the diagnosis and treatment of pyometra, please see our page entitled “Pyometra“.
Pyometra is a serious infection of uterine tissue which is reported to affect about 23% of intact female dogs at some time in their life. Pyometra kills about 1% of intact female dogs. 44,45 In theory, removal of the ovaries and uterus by means of ovariohysterectomy (OVH) should eliminate the risk of pyometra. Reality proves otherwise.
Changes in the canine uterus affected by pyometra
On this website, we noted that the 2007 systematic review83 we relied upon included as a benefit of spay: “nearly eliminates the risk of pyometra.” We drew attention to the use of the term “nearly” and we pointed out it is not uncommon for surgeons to inadvertently leave some portion of the uterus behind in a spay procedure. The “stump” of uterine tissue, as it is termed by veterinarians, is very susceptible to pyometra. Further, when a uterine stump develops pyometra, diagnosis is often delayed because it is initially assumed that there is no uterine tissue remaining after a spay. The delay can be very dangerous as the infection can spread rapidly.
Our research revealed that:
“A true stump pyometra is an uncommon problem which refers to a hormone (progesterone) mediated infection of a remnant of the uterus… a stump pyometra requires that residual uterine and ovarian tissue are present.”
How could parts of the ovaries and uterus be left after spay? We decided to take a closer look at the actual spay surgery and its complications as discussed among vets performing spay.
The oft-referenced “Textbook of Small Animal Surgery” 110 states that ovariohysterectomy (OVH) has the same complications as any abdominal procedure, e.g. anesthesia complications, delayed wound healing, suture abcesses and infection, and self-inflicted trauma to the wound. Additional complications specific to spay surgery may be more immediate:
- hemorrhage (the most common cause of death),
- fistulous tracts-typically due to braided, non resorbable suture material used as ligatures
- ligation of a ureter
More long term complications would include:
- ovarian remnant syndrome
- uterine stump pyometra
- uterine stump inflammation and granuloma
- urinary incontinence in 11 percent to 20 percent of cases
- weight gain of 26 percent to 38 percent
“Veterinary Practice News” included an illuminating article titled, “The Dog-Spay Disconnect: It’s Time To Rethink This Formidably ‘Simple’ Procedure” (excerpted below):
“The everyday canine ovariohysterectomy (OVH) is a procedure that’s both hard to master and easy to underestimate. Is there any other routine procedure we perform that compares to the canine spay for its high degree of difficulty and annoying unpredictability, not to mention its impressive complication rate?…Not only does the OVH (or OVE) require a mastery of anatomy and high proficiency in tissue handling, it’s complicated by factors arising from the tremendous variability among dogs…
In other writings the author of this article (i.e., Dr. Patty Khuly) has endorsed tubal ligation and vasectomy as her choice of sterilization method for otherwise healthy dogs.
The laundry list of complications of the ovariohysterectomy (OVH) has led to a number of alternative procedures, each intended to provide protection from pregnancy with fewer complications. There is the ovarioectomy (OVE) which removes the ovaries and leaves the uterus undisturbed, the ovary-sparing surgery (OSS) which leaves the ovaries and removes the uterus like a human hysterectomy, and our preferred method to prevent pregnancy, the tubal ligation (TL) which removes no organs but instead disconnects the tube which carries the egg from the ovary to the uterus, therefore preventing pregnancy. Intact dogs have not had any treatment to prevent them from becoming pregnant. The following chart outlines the complications of each alternative.
Certainly we would look at the number and nature of complications when making a decision regarding reproduction in our female dog. Some complications may be more serious than others, and some complications may be able to be remedied, where others may not.
A commentary from the Journal of American Veterinary Medical Association discusses ovarian remnant syndrome (ORS). The commentary authors conclude that ORS is a result of functional ovarian tissue remaining after ovariohysterectomy (OVH) or ovariectomy (OVE). Retrospective studies indicate that ORS represents 17% to 43% of all complications after ovariohysterectomy (OVH) and is more common with inexperienced surgeons.
We also found a peer-reviewed analysis of the serious consequences of ORS, and the challenge of remedying ORS.112 The interval from OVH/OVE to diagnosis of ORS is 1 month–10 years. Exploratory surgery and excision of ovarian remnants is the treatment of choice. A complete exploratory surgery should be performed to ensure all ovarian tissue is removed. Ovarian remnants can be created by fracturing of the ovary during OVH/OVE and these remnants can be located anywhere in the abdomen and can require a lengthy search to uncover. In a study of 21 cases of ORS in dogs (19) and cats (2), the records show ORS is also associated with an increased incidence of ovarian neoplasia113 (tumors):
“In our study, 5 of 21 (23.8%) animals had neoplasms in the residual ovarian tissue, which is higher than the reported incidence of 6.25% in sexually intact female dogs.
It is clear the veterinary community cannot come to any agreement as to how to prevent canine pregnancy. The discussion among veterinarians reveals complications that had not generally been revealed to the pet guardian, and we find that truly disturbing. An article recently published in “Veterinary Practice News” commented upon studies comparing methods of preventing pregnancy in female dogs:
“Van Goethem, et al, also write: “The surgeon has to choose the least invasive, fastest and safest procedure.” If we agree with that basic principle—reminiscent of the “First, do no harm”…
“Do no harm“, as the article states, should always be the prime objective of any medical care/treatment. Considering spay is generally an elective procedure (a procedure not needed to address any medical abnormality), how is it the veterinary community justifies the risks of the actual spay surgery (OVH or OVE) that we have detailed above. And what about all the long term behavioral, orthopedic, neurologic and metabolic damage done by the endocrine disruption perpetrated by OVH or OVE? OSS and tubal ligation preserve the endocrine balance of the female dog while preventing pregnancy. However, tubal ligation is the least invasive, fastest and arguably the safest procedure, based upon the human experience. This research to understand more clearly the actual risks of the spay surgery has firmed our resolve to fight for tubal ligation of our female canine family members.