The Truth About Gonadectomy
This is a very important paper written by soon-to-be Dr. Connie Lawless, a junior veterinary student at Ohio State University College of Veterinary Medicine (Class of 2011). She wrote this for her Canine Theriogenology (study of reproduction) class and did a great job of covering the important medical drawbacks of spaying and neutering dogs. Before the animal welfare groups get all up in arms, there are good alternatives to removing the gonads. Vasectomy (males) and hysterectomy (females) can be done just as easily by a veterinary surgeon and will render the patient incapable of reproduction while preserving the vital hormones that the gonads produce. The importance of the ovaries and testicles is not restricted to reproduction.
Assessment of the general effects of gonadectomy on canines
Connie White Lawless, Ohio State University College of Veterinary Medicine, Columbus, Ohio. February 10, 2010
The AVMA currently recommends that dogs be considered for gonadectomy on a case-by-case basis due to adverse affects related to the surgery. Yet the majority of veterinarians continue to push spay/neuter procedures to their clients. The purpose of this assessment is to determine the risks and benefits to both male and female canine patients.
Hormones produced by the gonads have effects on many body systems and are not restricted to activity in the reproductive tract. In addition to the reproductive system, these hormones are essential in the development of secondary sex characteristics, maintaining skeletal homeostasis, body condition, cholesterol levels, energy levels, urinary continence, muscle tone, cognition, behavior and implicated in coronary artery health. Androgenic hormones also play a role in the immune system that may compound direct effects in some instances. Prolonged or increased exposure to these hormones is believed to increase the risk of certain neoplasias but there is also an argument to the protective properties these hormones display against specific types of neoplasia.
The female gonads are called ovaries and the main steroid hormones they produce are Estradiol-17b and Progesterone. The male gonads are called testes, which also produce steroid hormones. Testosterone production is the main endocrine function of the testes but small amounts of other androgens and estrogens are also produced.
Although the steroid hormones function similarly in both males and females, there are slight differences to their affects on the body and risk factors between the sexes. For this reason, each of the topics discussed will contain a break down of specific actions, concerns and risks relating to the two sexes separately.
Steroid hormones produced by the gonads are responsible for the development of secondary sex characteristics. In the bitch, early spay has been linked to under developed external genitalia. This abnormal conformation often leads to chronic vaginitis and vulvar dermatitis. In the male dog, the penis may develop slightly smaller than in the intact dog but without ramifications.
Pyometra in the intact bitch is a condition in which endometrial hyperplasia prevents the normal drainage of the uterus during diestrus. During estrus the cervix remains open for the transport of semen into the uterus and fallopian tubes. At this time, bacterial pathogens can gain access to the uterus. Comensal bacteria from the vagina also make their way into the uterus. During diestrus the cervix closes tightly to protect possible developing embryos. If the drainage of endometrial gland secretions is impaired, any bacteria present in the uterus will have an ideal medium for growth. In turn the uterus becomes distended with pus and bacteria. This is a life threatening condition that can be prevented by proper and complete removal of all ovarian tissue. Pyometra affects approximately 15% of bitches by 4 years old and 24% by age 10. Ovariohysterectomy is curative barring any severe complications such as septicemia or uterine rupture into the peritoneal cavity. Mammary neoplasia is another serious disease associated with intact bitches. The incidence of mammary cancer can be greatly reduced with gonadectomy depending on the age and reproductive status of the bitch at the time of spay. This will be discussed later with other neoplasias. In stud dogs, the incidence of benign prostatic hyperplasia is as high as 80% in dogs over 6 years of age. Medical treatments are available for the management of this condition and castration is preventative and curative. A neutered male dog will not experience prostatic hyperplasia but are at risk for prostatic neoplasia. Estrogen receptors are present in the prostate gland and the prostatic urethra. Sertoli cells in the testes convert testosterone to estrogens. The main estrogen produced in the testes is Estradiol-17b. Serum estrogen levels in the intact male dog are much lower than levels in the Spermatic vein thus exerting the majority of the estrogenic affects locally on the reproductive tract. Estrogens have been shown to induce growth in reproductive tissues but have also been shown in human studies to be useful in prostatic and breast cancer treatment. A metabolite of Estradiol-17b, 2- methoxyestradiol, has shown powerful activity in preventing neoplastic cell proliferation and impedes tumor angiogenesis and metastasis. Female dogs are widely used as a model for human breast cancer and male dogs for prostatatic problems due to the many similarities of these issues between the species. Although breast and prostatic cancer in dogs does not exactly correlate to the human diseases, the basic hormonal activity should be expected to be similar if not identical. Intact male dogs, whose risk of prostatic cancer is negligible, normally produce 2-methoxyestradiol whereas castrated male dogs that do not produce this estrogen are at moderate risk. Until a study is conducted to determine the effects of estrogens in preventing prostatic and other cancers in dogs, disease statistics suggest the possibility of a positive role in local estrogens in the prevention of some cancers.
Effects of steroid hormones on bone and cartilage
Current studies show that testosterone, estrogen and other androgens work together in maintaining skeletal homeostasis but that estrogen plays a much bigger role than testosterone and the weaker androgens. Although the complete effects of estrogen over bone metabolism have not been fully determined, multiple mechanisms of action are known. Estrogens increase renal absorption of calcium, which decreases the amount of calcium passed in the urine. Estrogens decrease the sensitivity of bone to Parathyroid hormone, which reduces the amount of osteoclastic activity to free calcium from bone. Osteoblasts, which rebuild bone, contain receptors for estrogen but this mechanism is not well understood. Estrogens also increase absorption of calcium in the intestines and amplify active levels of circulating 1-25-dihydroxyvitamin D. It has also been suggested that estrogens inhibit osteoclastic activity by acting on osteoclast progenitor cells in the bone marrow. Loss of estrogen also causes an increase in other factors that induce osteoclastic activity. Estrogen deficiency causes a rise in body fat which induces higher levels of monocyte-chemoattractant protein-1 secretion. This rise in MCP-1 increases active osteoclasts. In humans, especially postmenopausal women, accelerated bone loss due to decreased estrogen levels is well documented. This often leads to osteoporosis and pathologic fractures. The most common sites of osteoporotic bone fractures are the vertebrae, hip and the cortical-cancellous junctions of bones like the Radius. In dogs, increased bone remodeling of the pelvis, specifically the ilium, and an overall loss of spinal bone mass have been the most noted areas affected. Fractures and decreased bone healing have also been observed in gonadectomized dogs. An increased incidence of Cranial Cruciate Ligament ruptures after gonadectomy, particularly in large breed dogs, has also been documented. CCL rupture is often associated with obesity and most likely the reason there is an increased incidence in spayed and neutered dogs. Multiple studies show an increased incidence of hip dysplasia, which decreases slightly if the dog is over 5.5 months old at the time of gonadectomy. Reports state that there is a 70% increase in hip dysplasia in dogs less than 5.5 months old at the time of spay/neuter but approximately half of these dogs never develop clinical signs of the condition. The overall percent of increased risk, regardless of age, of developing hip dysplasia after gonadectomy was not mentioned. In dogs spayed or neutered six months before being diagnosed with hip dysplasia, an increased risk of 1.5 times that of intact dogs to develop clinical disease was found. Hip dysplasia is an end result from a number of different factors that cause joint laxity. After gonadectomy, decreased muscle mass and weight gain are common and often major contributors to the development of HD. It has also been suggested that due to the loss of estrogen after gonadectomy, bones do not receive the properly timed signals to stop growing and physeal ossification is delayed. With uneven bone growth or abnormal formation, joint laxity is a risk. Bone neoplasia also occurs at a much higher rate in spayed and neutered dogs than in the intact population.
Body condition, cholesterol levels and energy levels.
The most common adverse effect of gonadectomy in the dog is weight gain. This is true with most species after the influence of the gonadal androgens is lost. A spayed or neutered dog is more than twice as likely to suffer from obesity as intact dogs. Decreased muscle mass and increased body fat diminishes energy levels by numerous mechanisms. Obesity leads to conditions such as hypothyroidism, hyperadrenocorticism, pancreatitis and diabetes mellitus. After gonadectomy, there is a three times greater risk of developing hypothyroid in both sexes. Some researchers believe this may be due more to the loss of effects of sex hormones on the immune system than to the direct influence on the thyroid. A study done with mice found there was an increase in severity of autoimmune thyroiditis following gonadectomy. It has been speculated that the same mechanism is at work in dogs.
Most research papers are heavily weighted to urinary incontinence in female dogs and very little can be found regarding the affects on male dogs. Although gonadectomy does cause an increased risk of urinary incontinence in both sexes, the effects are more significant in females. Less than 0.4% of intact female dogs suffer from urinary incontinence whereas up to 20% of spayed females suffer from this condition. Some experts suggest the percentage of female dogs affected by estrogen responsive urinary incontinence after gonadectomy may be as high as 40% but that studies have not included a large enough population of animals to be accurately representative. The age of the dog at the time of spay greatly changes the risk and severity of urinary incontinence. Dogs under 3 months of age at the time of gonadectomy are among the most often and worst affected. Urinary tract infections of a chronic or recurring nature are up to 4 times more likely in a spayed than intact female.
Adverse Vaccine Reactions
Adverse reactions to vaccines are reportedly 27-30% more likely in gonadectomized dogs than intact dogs with females being at higher risk than males. Sex hormones are important factors in the body’s ability to mount a proper immune reaction. Mixed breed dogs are at the lowest risk for these reactions.
Changes in cognition can be expected to some degree in all geriatric canines. Testosterone and estrogen are known to have neuroprotective qualities at the cell level. Currently studies on human Alzheimer’s patients to determine how much these hormones protect against cognitive impairment are being conducted. Cognitive impairment of geriatric dogs includes disorientation, general changes in behavior, interactions with other members of the household, voiding and defecating in the house when previously house trained and a change in usual sleep patterns. Gonadectomized dogs are more likely to progress from a mild state of impairment to a severe state of impairment.
Studies show that most behavior problems are not improved with gonadectomy and many are actually exacerbated. The sex of the dog and its age at the time of surgery suggest that there are different risks between the sexes. In males, age at the time of neuter is significant in determining the risk of certain behaviors but does not appear to affect risk in females. Males neutered before 5.5 months old are more likely to become aggressive with family members and to exhibit excessive nuisance barking. The severity of many behavior issues is breed specific but an increased incidence of aggressiveness toward owners and strangers has been noted in female dogs after spay. Where sexual behavior is concerned, one study shows that sexually dimorphic behavior such as mounting, posturing, thrusting and even ejaculation can be activated in gonadectomized mice by administration of a dopamine agonist. Further testing showed that the gonadectomized mice on dopamine agonists had equivalent levels of catecholamine in regions of the brain associated with sexual behavior as the intact mice. It is not understood exactly where the dopamine activates this behavior but it is believed to be at an Estrogen receptor, Estrogen a receptor or even an estrogen independent pathway. This strongly suggests that sexual behavior is not only controlled by sex hormones but by other mechanisms as well.
One of the major reasons for elective spay of female dogs is to reduce the risk of mammary neoplasia. Mammary neoplasia is the most common tumor of female dogs and its overall occurrence is 3.4% with over half of those cases being malignant with metastasis most often to the lungs. Reducing the incidence by spaying female dogs is depended on age and reproductive status at the time of surgery. In dogs where spays occur before the first estrus cycle, the risk is minimal. The amount of reduced risk of mammary neoplasia after spay decreases with age and number of cycles until approximately 30 months old or after 3 cycles after which time the risk is not reduced. In bitches that have had a cycle and a litter, spay reduces her risk more than if she had not had a litter and had been spayed after her first estrus. Although any breed can get mammary neoplasia, certain purebred breeds are at high risk and this should be considered when evaluating the necessity of gonadectomy.
The incidence of testicular neoplasia in dogs is less than 1% with low morbidity. Testicular neoplasia in the dog is not likely to metastasize prior to diagnosis. Neuter surgery is curative and no adjunctive therapy is needed.
Prostatic Adenocarcinoma has a low incidence, approximately 0.6% in dogs, but is very aggressive and treatment options are minimal. The Bouvier breed is the only breed documented to have a higher than the average incidence of Prostatic Adenocarcinoma. Neutered male dogs are 4 times more likely to be affected than intact dogs.
Osteosarcoma is an aggressive cancer that affects male and female dogs. Increased risk is associated with spay or neuter, age at spay or neuter, breed and size. Gonadectomy increases the risk of Osteosarcoma to twice that of intact dogs. Early age gonadectomy is associated with even more elevated risks. Large sized dogs and more specifically, tall dogs with longer bones have an increased risk of Osteosarcoma. Rottweilers have a high risk of Osteosarcoma. If spayed or neutered before one year old, Rottweiler females have a 25% chance and males a 28% chance of being affected.
Transitional Cell Carcinoma of the Urinary Bladder is a fairly uncommon neoplasia and constitutes less than 1% of the tumors affecting dogs. The incidence of TCC in spayed and neutered dogs is 2-4 times that of intact dogs.
Hemangiosarcoma is a common and devastating neoplasia in dogs. Females have a higher incidence than males. The two most common forms of Hemangiosarcoma in the dog are splenic and cardiac. Neutered males have greater than 1.5 times the risk of intact males. It has been documented that spayed females are at a risk greater than 2 times that of intact bitches for the splenic form and more than 5 times greater risk for the cardiac form. It is important to recognize the high risk breeds such as German Shepherds, Hounds, Terriers, English Setters and Bulldogs when determining if spay should be considered.
It is this author’s conclusion that the AVMA’s stance on gonadectomy should be taken seriously by all veterinarians. Client education on the matter should be fully disclosing of the benefits and risks to their pet. The risks of castration greatly outweigh the benefits in male dogs. The decision to spay a female dog is more involved and must include a comprehensive evaluation. The breed, age, sex, health and reproductive status of each animal should be assessed. Given the breed and signalment, specific individual benefits and risks must be weighed before a gonadectomy is performed.
Hormone replacement therapy options to reduce the complications of gonadectomy are currently being studied. In the future, with good owner compliance and the implementation of hormone replacement therapy, the benefits may outweigh the risks in almost all cases. Until then, the health and well being of the dog and its owner must be carefully considered before a routine spay or neuter.
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