Gonadectomy is the most frequently performed elective veterinary surgery (estimated prevalence of >60% in dogs and cats) in the United States1 and is commonly recommended for population control, reduction of hormonally driven behaviors, disease treatment or prevention, and pet owner convenience.1-4
In the United States, canine gonadectomy has traditionally been performed at ≈4 to 6 months of age, after puppies complete their vaccine series. From a technical perspective, surgery at this age or younger is easy, fast, and safe because of small patient size, lack of body fat, and rapid recovery; however, recent studies suggest gonadectomy before skeletal maturity can have adverse effects, particularly in certain dog breeds.2,4 More owners and clinicians are thus reconsidering their opinions on timing of gonadectomy and whether it should be performed. There are no randomized, controlled, lifetime studies to provide unequivocal evidence on appropriate timing of gonadectomies3; therefore, the decision as to when and if a patient should be neutered should be based on the individual patient, owner, and available data.
Hormone-Associated Conditions Treated or Prevented by Gonadectomy
Conditions preventable or treatable by gonadectomy include testicular, ovarian, and uterine cancers; pyometra; prostatic hyperplasia; and endometrial polyps.5,6 Gonadectomy also improves the chance for successful treatment of hormonally induced conditions (eg, prostatic abscesses and cysts,7 vaginal prolapse and hyperplasia,8 perianal adenomas9). Ovariectomy may contribute to control of diabetes mellitus10 and regression of vaginal leiomyoma.11
Ovariectomy & Risk for Mammary Neoplasia
Gonadectomy before sexual maturity reportedly reduces the overall risk for mammary tumor development12-14; however, a systematic review found moderate to high risk for bias in published canine studies.14
The most quoted—and misquoted—study regarding mammary tumors and gonadectomy reported that dogs spayed before the first or second estrous cycle had 0.5% or 8%, respectively, of the risk of intact, multiestrous dogs, and that dogs spayed after 2 or more estrous cycles had a 26% relative risk.13 This information can be misinterpreted by assuming the actual rates of mammary cancer are 0.5%, 8%, and 26% of female dogs, depending on the timing of ovary removal; however, these numbers represent relative risk as compared with intact dogs. Application of these statistics therefore requires knowledge of mammary tumor incidence in intact females. For example, one study reported an annual incidence of 250 cases per 100,000 dogs, 73.4% of which were intact.15 Based on this study, the average annual incidence for intact females would therefore be 184 out of 100,000 (0.18%) dogs. Using the relative risk percentages from the study,13 the estimated annual incidence per 100,000 dogs spayed before their first, second, or third estrous cycle would be 1 (0.001%), 15 (0.015%), and 48 (0.048%), respectively, in that population.
Risk for Mammary Tumor Development
In patients in which risk for mammary cancer is the underlying reason prepubertal gonadectomy is recommended, breed predisposition to the disease should be considered. According to a Swedish insurance study of >260,000 female dogs, mammary tumors were most often reported in Leonbergers, Doberman pinschers, Bernese mountain dogs, Welsh terriers, English springer spaniels, American cocker spaniels, and boxers.16 For each of these breeds, the estimated likelihood of developing mammary tumors over a lifetime was ≥35%; conversely, estimated likelihood was ≤5% for basenjis, collies, Finnish Lapphunds, Lancashire heelers, Norwegian Buhunds, Norwich terriers, Pomeranians, pugs, and Siberian huskies.16
In another study of >7,000 female dogs in the United States, no mammary cancers were reported in intact or gonadectomized Bernese mountain dogs, boxers, miniature schnauzers, pugs, Saint Bernards, Shetland sheepdogs, or West Highland white terriers, but a high incidence was reported in American cocker spaniels and English springer spaniels.4 Based on these studies, owners of cocker spaniels and English springer spaniels may be counseled to consider ovariectomy before the first or second estrous cycle; however, mammary cancer may not play a decision-making role for owners of West Highland white terriers or Shetland sheepdogs. The discrepancy regarding Bernese mountain dogs could reflect differences in regional genetics or follow-up: the study of Swedish dogs16 followed patients to 10 years of age, whereas in the US-based study,4 mean age at follow-up was <6 years.
Ovariectomy for Pyometra Prevention
As with mammary tumors, timing of, or even need for, gonadectomy for pyometra prevention may depend on the breed of the patient.16,17 Pyometra usually occurs in dogs >4 years of age and is therefore preventable with ovariectomy by this age in most breeds; however, Dogues de Bordeaux may be presented at a younger age (mean, 3.3 years).16,17 Overall, ≈19% of intact females develop pyometra by 10 years of age, but the proportional hazard is ≥50% in Bernese mountain dogs, Bouvier des Flandres, bull terriers, Irish wolfhounds, keeshonds, Leonbergers, Newfoundlands, rottweilers, and Staffordshire bull terriers.16 Owners of high-risk breeds who believe there is no right time for gonadectomy may need to be counseled on the signs and complications of pyometra to aid in decision-making.
Increased Risk for Joint Disease
For some dog breeds, particularly large breeds, gonadectomy increases the risk for joint disorders by 2 to 5 times that of intact dogs.4,17-20 For example, in golden retrievers, joint disease was diagnosed in 27% of males neutered before 6 months of age and in 5% of males left intact.4,19 Rates of joint disease in male and female German shepherd dogs gonadectomized at <1 year of age were 21% and 16%, respectively, compared with 7% and 5% in dogs left intact.20
Not all large breeds are affected equally. Neutering before 6 to 12 months of age was associated with significant increases in joint disorders in male Bernese mountain dogs, Labrador retrievers, rottweilers, and female Saint Bernards but not in collies, Doberman pinschers, Great Danes, or Irish wolfhounds.<sup4 sup>
Effects of gonadectomy on the risk for joint disease can also be related to sex. For example, neutering before one year of age increased the risk for joint disease in male cocker spaniels, miniature poodles, and beagles but not in females of those same breeds.4
Increased Risk for Urinary Incontinence
Although urinary incontinence does not directly cause death, it may result in euthanasia because of quality-of-life issues for owners. Urinary incontinence is most often reported in spayed, large-breed dogs and is rare in intact dams.18,21-26
A systematic review found that most canine urinary incontinence and timing of gonadectomy studies had a moderate to high number of errors that biased the conclusions; however, weak evidence indicated that ovariectomy, particularly before 3 months of age, increased the risk for incontinence.23 In a more recent study, most cases of urinary incontinence occurred in dogs spayed at <1 year of age, with some breeds at significantly greater risk.4 For example, urinary incontinence was diagnosed in 25% of Doberman pinschers spayed before 6 months of age and in 19% of those spayed between 1 and 2 years of age.4
Other breeds with high rates of urinary incontinence after spaying included English springer spaniels, German shepherd dogs, rottweilers, Shetland sheepdogs, and West Highland white terriers.4 Predisposed breeds may benefit from longer hormone exposure with intact ovaries.
Possible Increased Risk for Nonreproductive Cancer
Other than tumors of the reproductive tract, it is difficult to determine whether gonadectomy increases the risk for cancer, as gonadectomized dogs often live longer, which increases the risk for cancer.3,18 Some studies indicate that the effects of gonadectomy on nonreproductive cancer risks are breed- or gender-specific. For example, gonadectomized vizslas developed mast cell tumors at an earlier age than intact vizslas, and gonadectomized female golden retrievers were at increased risk, whereas males were not.4,19,27
Complications & Cost of Convenience & Delayed Surgeries
Some owners consider elective gonadectomy unacceptable or deforming; however, gonad-sparing surgeries to permanently prevent reproductive capabilities or adverse effects of estrus may still be requested. These convenience surgeries can have positive and negative effects. For example, male dogs can be vasectomized to prevent delivery of sperm during copulation. Although vasectomy is a simple surgery with few complications,28,29 vasectomized dogs continue to have effects of testosterone, including libido-driven behaviors and prostatic hyperplasia.3
Ovary-sparing hysterectomy requires removal of the entire uterine horns and uterine body.28 Resection of the cervix is also recommended because glandular endometrial tissue can extend into the cervix, which could result in vaginal discharge, endometritis, or stump pyometra.30 Hysterectomy requires a longer incision than ovariohysterectomy because of the need for complete cervical resection, careful dissection to spare the urethra, and complete removal of the uterine horn tips. Ovary-sparing hysterectomy has no published long-term follow-up, but dams could suffer life-threatening conditions (eg, vaginal rupture, sperm peritonitis) if allowed to mate.28 Vulvar and behavioral signs of estrus and attraction to males should be expected, and vaginal discharge could occur if glandular tissue remains.
Delaying neutering increases anesthetic costs because of increased patient size. Ovariohysterectomy in adult dogs is more expensive and more difficult than in puppies, and complication rates are higher with larger patients and longer surgeries.31
Counseling Is Required
Owners of dogs left intact may need counseling for managing libido-driven behaviors of males and isolating females during estrus. Owners may opt to place belly bands (ie, washable wraps that catch urine) on male dogs that mark indoors or diapers on female dogs that have vaginal discharge. Female dogs should not be taken to the park during receptive periods, nor should they be left alone in yards with low or electronic fences. Intact dogs should be leash- and crate-trained to provide extra control. Gonadectomized dogs have an increased risk for obesity and, therefore, need to be fed and exercised appropriately to prevent weight gain.3
In My Opinion …
Dogs should be allowed to reach musculoskeletal maturity (ie, be fully grown, with a fully functional urethral sphincter) before being neutered. Breed type and temperament should also be considered.
Rottweilers provide an excellent case study for using research to determine timing of gonadectomy. In one longevity study, rate of mammary cancer in rottweilers was 7.9%, with a median age of 8.5 years at the time of diagnosis and a 37% case fatality; the rate of pyometra was 6.6%, with a median age of 5.4 years and case fatality of 7%.32 These results indicate that prepubertal or adolescent ovariectomy could improve outcome; however, ovary exposure >4.2 years was associated with a lifespan 17 months longer than for dogs with shorter ovary exposure.32 Life expectancy for females that developed mammary cancer was similar to the overall population. Bone sarcoma and lymphoma, however, had significant negative effects on life expectancy.32
Rottweilers have a 12.6% risk for bone sarcoma, and dogs that undergo gonadectomy before 1 year of age have an incidence rate of >25% compared with rates of 7.6% to 10.5% if left intact or gonadectomized after 3.5 to 5 years of age.33 Because bone sarcoma has a mortality rate >90%, leaving a rottweiler intact for at least 4 years is worth the risk for mammary tumors. This also may decrease the risk for urinary incontinence. The rate of urinary incontinence was 1% in intact female rottweilers and 4% and 6% for those spayed at <6 months and 6 to 11 months, respectively.4 Research may not always be the deciding factor. In the author’s opinion, if a dog becomes aggressive during estrous cycles and attacks humans or other animals, the ovaries should be removed immediately and without hesitation.
Multiple factors, including breed and age of the dog and inclinations and needs of the owner, should be considered when determining whether to perform gonadectomy, as well as the appropriate timing. Whether a dog is neutered or left intact, owners should be informed of common breed and sex conditions, and the dog should be examined for those conditions on subsequent physical examinations.
There is no single or definitive source of information on effects of gonadectomy for each breed, and most current articles have some bias. Current evidence should be evaluated and the positives and negatives should be considered for each patient and owner before a recommendation is made.