An Introduction To Spaying, Neutering, Disease, & Behavior
Sterilization is the process of desexing - neutering for males - spaying for females. This process has been historically performed for unwanted outcomes relating to unexpected births, undesirable behaviors (marking, humping, etc.), and for specific medical conditions and diseases.
Neutering rates in the UK are around 40%, while NA and Australia are around 80%.
This is still a heavily debated topic with studies showing a multitude of results with specific factors such as breed, age, etc. being important factors.
CASTRATION
The removal of the gonads (gonadectomy) in males, or ovaries and uterus (ovariohysterectomy) in females prevents the production and utilization of testosterone, estrogen, and progesterone.
Keeping dogs intact (no castration) leaves glands within our dogs and allows them to utilize their sex hormones which has many proven benefits.
Statistics: Quick reminder! A 100% increase may sound like a lot, but if the sample size (population studied) was only 1 dog, this ONE HUNDRED percent increase only represents two dogs. I’d rather have an 80% chance of a cough than a 10% risk of a heart attack!
Also say, the relevance of a German Shepherd Dog’s risk for hip dysplasia compared to say, a chihuahua.
MAMMARY NEOPLASIA (BREAST CANCER)
The most common type of cancer is carcinomas which make up 80-90% of cases. This type of cancer resides in the epithelial tissue, a layer covering skin, glands, and organs.
Males only make up around 2.7% of these cases. Around 50% (other studies ~42%) of tumors were found in females of mammary neoplasia tumors. 82% of tumors originate in female reproductive organs. Of those, 50-60% were benign, leaving 40-50% as cancerous (malignant). Prognosis involves tumor size, type, grade, mode of growth, and lymph node status.
A study from Santos et al. studied 85 females affected by spontaneous malignant mammary neoplasia and followed them over a 2-year postoperative period. The overall 2-year survival rate was only 48%.
In dogs, most mammary tumors that are going to cause death do so within 1 year. Sarcomas are associated with shorter survival times than carcinomas. Other factors, including size of tumor, lymph node involvement, and nuclear differentiation, also affect the prognosis. (Merk’s)
This disease is seen in 1 out of every 385 intact females.
A study by Schneider et al., found that females that were spayed before any estrus cycle had a 0.5% risk of mammary cancer. After one estrus cycle, 8%. And dogs with 2+ estrus cycles are at a 26% risk.
Mammary tumors have been observed at lower rates when spayed before two years of age compared to older than two years of age.
Breed specifics have been noted in this area of research with hunting breeds being at higher risk. A study from Bostock found high-risk dogs included the Poodle, the English Spaniel, the Brittany Spaniel, the English Setter, the Pointer, the Fox Terrier, the Boston Terrier, and the Cocker Spaniels; with lower than average incidence in the Chihuahua and the Boxer. GSDs have also been added to the high-risk group.
PYOMETRA
Pyometra is an infection of the uterus. Following a female’s season, the hormone progesterone remains elevated for upward of 2 months. This causes the lining of the uterus to thicken, preparing for pregnancy. When pregnancy does not happen, this thickening continues, which can lead to cysts. The cysts secrete fluids that create an ideal environment for bacteria. When the uterus thickens, it also prevents the uterus from contracting properly, to expel its contents.
The more cycles a female progresses through, the higher the chances of developing Pyometra. It’s most commonly seen in older dogs but can happen at any age.
The uterine wall thickening prevents white blood cells (WBCs) from accessing the sperm (an "invader") to neutralize it. Unfortunately, this also prevents the WBCs from fighting off REAL infections, such as Pyometra.
Symptoms can include discharge around the tail area, on their skin, or bedding. You may see behavioral changes such as fever, lethargy, anorexia, and depression.
A 2012 study, “Breed Variation in the Incidences of Pyometra and Mammary Tumors in Swedish Dogs” studied an insurance database of more than 10 years of information. This data contained 260,000 females. This data resulted in about 1 million dog years on record. The study found that 19% of intact females will develop pyometra by or at the age of 10. The top 10 breeds at the highest risk (50%+ by age 10) for pyometra include Bernese Mountain Dog, Great Dane, Leonberger, Rottweiler, Irish Wolfhound, Staffordshire Bull Terrier, Keeshond, Bull Terrier, Newfoundland, and Bouvier des Flandres.
This disease is preventable with an ovarian hysterectomy.
TESTICULAR NEOPLASIA
Testicular neoplasia is a testicular tumor. They are found in three common types which include seminomas (sperm-making cells), interstitial cells (Leydig tumors - produce the actual testosterone), and Sertoli cell tumors (aid in sperm development).
Symptoms are often hard to recognize. Signs include a mass/lump, uneven-sized testicles, or generalized swelling of the scrotum.
A Slovakian study from 2014 studied 1975 dogs post-mortem. 206 of these dogs had testicular tumors. There were 301 tumors. 47.8% were Seminomas, rarely spreading. 28.6% were Interstitial cell tumors, usually benign, but 19.6% were Sertoli cell tumors, the riskier, more aggressive tumors.
Malignant tumors will show symptoms based on the location of the mass(es). This can include weight loss, decreased appetite, lethargy, or vomiting. If the tumor has spread to the lymph nodes near the urinary system or to the prostate gland, signs may include difficulty urinating or defecating.
Bush et al. tested 347 cases of testicular tumors across 71 breeds and found no relevance claiming there was no apparent breed predisposition amongst the 71 breeds involved. It's a view supported by Santos et al., who found no predisposition across his 497 dogs.
However, Liao's 12-year retrospective study found increased rates in Maltese dogs. Our Slovakian paper from earlier cites German Shepherds, Collies, and Poodles top of the pile, with Nordvedt et al., study of 345 testicular tumors finding sheepdogs and collies being five times more likely to have testicular tumors than the overall average. A further variety of studies claim correlations with Boxers, German Shepherds, Afghan Hound, and Weimaraners.
Although no studies within dogs, humans who have had vasectomies showed no correlation to testicular tumors.
Severity matters too. A 2015 paper “Current Perspectives on the Optimal Age to Spay or Castrate Dogs and Cats”, states that less than 1% of intact male dogs will die from testicular cancer.
BENIGN PROSTATIC HYPERPLASIA - BPH
There are several non-neoplastic diseases of the prostate, but the most common is Benign Prostatic Hyperplasia, or BPH for short.
The prostate aids in the formation of fluids used to transport semen. BPH in older dogs is a natural process due to aging and hormonal influence on the prostate gland. 75%–80% of intact dogs by the age of 6, and 95%–100% of intact dogs by 9 years of age. This consistency is seen due to an increase in dihydrotestosterone (DHT) receptors in the prostate.
Symptoms can include a thin stream of urine, a longer urination duration, or compression of the colon resulting in problems defecating. Benign Prostatic Hyperplasia is the underlying cause of most other prostate disorders, including prostatitis or bacterial prostatitis.
Of course, like mammary neoplasia, removal of the reproductive organs prevents the development of the disease. Castrated dogs are less likely to develop BPH due to the atrophy of the prostate (due to the lack of testosterone).
A study supplemented castrated dogs with testosterone and found that not only did testosterone treatment develop BPH in young dogs who would otherwise not experience the problem, but also brought back BPH in older dogs.
Studies in humans show no impact of vasectomies and the rates of BPH.
MEDICAL COUNTER ARGUMENTS TO DESEXING
A common (and valid) concern with keeping your dog intact (reproductive systems untouched) is the closure of long bone epiphyseal plates. Maintaining the hormones within the body prevents a higher prevalence of joint disorders and an impact of cranial cruciate ligament (CCL) rupture in dogs.
A study in 2013 by Gretel Torres de la Riva et al. looked at 759 client-owner, intact and neutered female and male Golden Retrievers between the ages of 1-8 years old.
They were split into three categories:
- Intact
- Neutered less than 12 months old
- Neutered older than 12 months
Male Golden Retrievers neutered <12mo were twice as likely to develop hip dysplasia compared to intact males, with no difference in females.
There were zero cases of CCL (cranial crucial ligament) in intact males or females, or any neutered >12mo. But in early <12mo neutered males and females, rates were seen at 5.1 and 7.7% respectively.
Hart et al. in 2014 replied to this paper. They looked at 13 years of neutering statuses and specific age groups. They were observing for correlations in hip dysplasia, cranial cruciate ligament tears, and elbow dysplasia.
The three groups they isolated were:
- <6mo
- 6-12mo
- 1-2yrs
- 2+ yrs
Approximately 5% of intact males and females Labrador Retrievers had joint disorders. Neutering at age <6mo doubled the incidences in both sexes.
The Labs were no more or less likely to suffer from hip dysplasia as a result of early neutering, but early neutered males were almost 3x more likely to suffer from CCL issues and 8x more likely to suffer from elbow dysplasia.
Neutering Labradors at age <6mo is also correlated with a 3x chance for hip dysplasia, 6-11mo old 2.9x, and older than 2 years old at 2.4x chances.
Teracini and Glickman in 1998 compared 3062 dogs with osteosarcoma (bone tumors) against a control sample of 3959 dogs. They found neutered dogs were 2x as likely to suffer from osteosarcoma, with risks increasing with age, weight, and height. The highest rates are seen in large and giant breeds, with small breeds showing a reduced risk.
Some evidence points towards increased odds of lymphoma in some females of certain breeds. A study of 15,000 canine lymphoma patients was compared to a database of 1.2 million dogs. They found that intact females were around half as likely to develop lymphoma compared to spayed females. Breed-specific studies have also shown a 3-4x increased likelihood in Golden Retrievers and Vizslas.
Sundburg et al. reviewed 90,090 records from a 15-year timespan and found that neutered dogs had a significantly greater risk of several immune disorders when compared to intact dogs. These disorders include atopic dermatitis, autoimmune hemolytic anemia, hypoadrenocorticism, hypothyroidism, immune-mediated thrombocytopenia, and inflammatory bowel disease.
A huge study of 2.2 million dogs from the Banfield report showed an average lifespan of 11 years, with spayed dogs living 11.6 years compared to intact at 9.5 years, that’s a 23% difference.
SEX HORMONES & BEHAVIOR
We often see an overlap of sexual-related behaviors and the period of adolescence. This is due to increases in vasopressin and oxytocin (which affect relationships and social play). Dopamine also peaks during this time increasing the need for mental and physical stimulation. Other adolescent behaviors can include roaming, sensation seeking, increased risk-taking, and a lack of self-control. This can confuse the line between sexually and adolescent-motivated behaviors.
Maarschalkerweerd et al. in 1997, followed 122 dog owners after castration. They found decreases in sexual behavior, roaming, and abnormal urination. These behaviors were reduced in about 60% of the dogs. Hopkins et al.’s retrospective study of 42 dogs found that castration produced a reduction in roaming in over 90% of dogs, mounting in over 60% of dogs, and marking for around 50% of dogs.
Eckstein Neilson and Hart looked at 57 dogs castrated over the age of 2 that had one or more behavior problems mentioned above. They found moderate improvement in around 60% of the dogs and greatly improved results in 40% of the dogs. They found no correlation between age and the likelihood of behavior change success rates. (These dogs were post-adolescence).
These two studies above were “owner-based” questionnaires which may lead to inaccuracies in reported behaviors.
Beach in 1970 studied 7 sexually experienced male dogs that were castrated and tested for mounting behavior between 21-36 months of age. Beach found that castration did not affect latency or rate of mounting behavior for these dogs.
A 2015 study from Chile used GPS collars and showed no change in the free-roaming dogs' home range as a result of castration.
Most studies on neutering found a significant decrease in urinary marking behavior in male dogs regardless of the age of desexing.
Phantom pregnancies, or pseudo pregnancies are common, affecting between 50-75% of female dogs. There are breed correlations as well. The higher prevalence is seen in Boxers, Afghans Hounds, Dachshunds, and Beagles. Phantom pregnancies can result in maternal-type aggression. There may also be nesting, collecting toys and items, to prepare for the “birth”.
Now, why do we see such variety in behavior and sex hormones?
Testosterone promotes self-confidence in dogs. A dog who also happens to have low cortisol levels may be more impulsive. In this case, the decrease in testosterone may have beneficial effects. While a fearful dog may worsen if castrated.
Eisenegger et al. in 2017 looked at 181 human males. There was a simple math test. The first test was in a non-competitive setting, and the second was competitive. Testosterone was measured before and 20 minutes after each test. They found two correlations of testosterone, increased confidence, and competitiveness.
Starling et al. study from 2013 reviewed the boldness of 1054 dogs using the C-BARQ questionnaire. They looked at a shy-bold axis. They found males bolder than females, and intact dogs bolder than neutered dogs.
A paper titled “Effects of ovarian hysterectomy on reactivity in German Shepherd dogs” took 14 dogs aged 5-10 months. These dogs were placed into a spaying group and an intact group. Placing them in scenarios of an unfamiliar human, and then an unfamiliar dog. The results showed spayed dogs with “higher reactivity”.
Similarly, Balogh et al. studied 58 female Labradors. They concluded that owners of spayed dogs described more frequent or more intense fear reactions in their animals in response to loud noises, unfamiliar objects approaching on or near the sidewalk, or if they were approached by unknown dogs barking, growling, or jumping.
Farhood et al. 2018 surveyed 15,370 dog owners and found gonadectomy nor age at gonadectomy showed any association with aggression toward familiar people or dogs. They found a significant increase in the odds of moderate or severe aggression toward strangers for gonadectomized dogs compared to intact dogs. These dogs were aged 7-12 months and were 26% more likely to demonstrate aggression toward strangers later in life. This study also excluded dogs who were being neutered for behavioral concerns, leading to altered results.
Another C-BARQ study looked at 6235 male dogs and found that the longer a male was without his testicles represented an increase in fearfulness and aggression.
Balint says it quite concisely: ‘neutering has an ambiguous effect on the occurrence of problems within the different types of aggression within dogs’.
As we can see there are a multitude of factors in play. Many physiological processes rely on one another to maintain proper balances of emotions and behaviors. There are personal factors that can help you decide what’s best for you. As with everything, do your research and make an educated decision. There is no “right” answer on this subject.
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