Facts About this Safe and Effective Procedure
Pediatric spay/neuter is the subject of ongoing debates among veterinarians that is fraught with misinformation, misconceptions and high emotions. Although millions of domesticated animals have been surgically sterilized, many veterinarians believe sufficient conclusive research has not been conducted to determine the best age or reproductive stage of life to spay and neuter dogs and cats.
However, studies have been conducted that show that pediatric spay/neuter is safe and effective in both the short and long term. This information can help allay many of the veterinarian’s fears so they may embrace the concept as readily as they embrace neutering at 6 months of age.
Early Age Spay/Neuter Defined
The harshest criticism by veterinarians of early age neutering is usually reserved for surgeries performed on animals as young as 6-8 weeks of age or under 2 pounds of body weight. But early age spay/neuter should be broadly defined as surgical sterilization procedures performed on animals who are 6-16 weeks of age or under the traditional age of 6 months. Using that definition, surgery performed on a 4-month old female animal would be considered a pediatric spay.
Because the term "early" implies that the procedure is being performed prematurely, some veterinarians proposed that alternative language might be more acceptable. Some alternative terms for early age spay/neuter include:
Many veterinarians are not aware of the different theories that have been advanced regarding the timing of spaying a female cat or dog. Both veterinarians and the general public might be surprised to know that in the early 1900s, veterinarians advocated spaying bitches between 3 and 6 months of age, or even prior to weaning, and castration was done as early as 4 weeks of age. At one time it was believed that it was beneficial for animals to have a litter before being spayed, while another prevailing school of thought, until fairly recently, was that animals should go through one heat before being spayed.
Many veterinary colleges are currently teaching that spaying and neutering, also known as gonadectomy, can be done safely at any age, but believe that pediatric spay/neuter is a tool mainly for population control for shelter animals only. However, pediatric spay/neuter should be considered for animals belonging to the general public as well.
Revisiting the Six-Month Recommendation
Six months of age is generally considered to be the standard recommendation for spaying and neutering puppies and kittens. It is unclear from the scientific literature how that conclusion was reached.
It is now known that spaying an animal before the first heat prevents the development of mammary gland tumors later in life. Since kittens may go into heat at 4 months of age, waiting until 6 months risks accidental pregnancy and loses the protection against mammary gland cancer.
It would appear that decisions about when to spay and neuter are based more on the individual practitioner's comfort level and familiarity with the surgical technique and anesthesia rather than on any sound scientific or medical evidence.
The six month age requirement for surgery came into question in the late 1970s when shelters encountered difficulty getting adopters to comply with contractual agreements to neuter their newly adopted pets. Despite various incentives, many adopters simply refused to abide by the agreements once they had acquired the animals.
Some shelters found that litters from animals they had adopted out were being brought back to them, and that they were thus actually contributing to the overpopulation problem. They decided the best solution would be to neuter the animals before they were adopted, but the six month age restriction meant that puppies and kittens could not be altered.
Once it was determined that no compelling medical reason could be found in the veterinary literature to wait until the animals were six months of age, pediatric surgeries began to be performed. Dr. Leo Lieberman is the acknowledged pioneer of pediatric spay/neuter. He began performing the surgeries in the late 1970s, and they have been performed by shelters ever since.
A Growing Body of Evidence
In 1993 Faggella and Aronsohn published surgical and anesthetic protocols in the Journal of the American Veterinary Medical Association (JAVMA) for safely neutering animals as young as 6 weeks of age. Although the surgeries had already been performed safely on thousands of shelter animals, these articles provided the much-needed research data to prove that the procedures were indeed safe to perform.
On July 18, 1993, the American Veterinary Medical Association (AVMA) House of Delegates approved a resolution on early age spay/neuter which stated:
“Resolved that the AVMA supports the concept of early (8-16 weeks of age) ovariohysterectomies/ gonadectomies in dogs and cats, in an effort to stem the overpopulation problem in these species.”
Aware of the controversy surrounding this statement they also added:
“The concept is for the benefit of animal shelter and humane society spay/neuter programs. Individual veterinarians have the right/responsibility to decide at what age they will perform the procedure.”
In 2004, the policy was revised and the “concept” portion of the statement was removed.
Throughout the 1990s, groups such as the American Animal Hospital Association (AAHA), American Society for the Prevention of Cruelty to Animals (ASPCA), American Humane Association (AHA), Cat Fanciers Association (CFA), American Kennel Club (AKC), Humane Society of the United States (HSUS), and the California Veterinary Medical Association (CVMA) endorsed pediatric spay/neuter.
Despite these endorsements and the body of evidence already gathered through research and anecdotal information from over 25 years of performing pediatric procedures, the debate still goes on. This information should help resolve some of the problems and concerns.
An often-cited concern regarding pediatric spay/neuter is a lack of sufficient scientific data regarding long-term consequences. The following are commonly discussed issues:
General Concerns about the Long-Term Effects
The results of studies of the long-term outcome of gonadectomies performed at an early age or traditional age in cats and dogs were published in JAVMA in the December 1, 2000 and January 15, 2001 issues, respectively. The studies were performed at the Texas A&M Veterinary College by Dr. Lisa Howe on 269 dogs and 263 cats from animal shelters.
The conclusion for dogs was that “with the exception of infectious diseases, prepubertal gonadectomy may be safely performed in dogs without concern for increased incidence of physical or behavioral problems during at least a 4-year period after gonadectomy.”
Shelters that held puppies long-term encountered problems with parvovirus. However, the authors of this paper did not conclude that prepubertal gonadectomy caused parvovirus. The puppies in the study were at an age where they were susceptible to parvovirus and housed in a shelter environment where parvovirus can be common; they developed parvovirus for these reasons, and not because they were sterilized as pediatric patients. (Studies have also shown that, unrelated to surgery, the longer animals are held in shelters, the more likely they are to become ill. Shelters that held puppies short-term did not encounter similar disease problems.)
The conclusion for cats was that “prepubertal gonadectomy may be performed safely in cats without concern for increased incidence of physical or behavioral problems for at least a 3-year period after gonadectomy.”
Another study addressing the long-term effects of pediatric spay/neuter was published in JAVMA in the February 1, 2004 issue. This study was performed at the Cornell University College of Veterinary Medicine by Dr. Vic Spain, who looked at the records of shelter animals (1,842 dogs and 1,660 cats) who were sterilized as pediatric patients. This study provided follow-up for as long as 11 years.
The conclusion for dogs was that “because early-age gonadectomy appears to offer more benefits than risks for male dogs, animal shelters can safely gonadectomize male dogs at a young age and veterinary practitioners should consider recommending routine gonadectomy for client-owned male dogs before the traditional age of 6 to 8 months. For female dogs, however, increased urinary incontinence suggests that delaying gonadectomy until at least 3 months of age may be beneficial.” It is important to note that the female dogs with reported urinary incontinence remained in their homes and were not relinquished to the shelter. The long-term Texas A&M study did not find similar results about urinary incontinence, and another study from 1992 showed a higher incidence of urinary incontinence in female dogs spayed AFTER the first estrus cycle.
The conclusion for cats from the Cornell study was that “Gonadectomy before 5.5 months of age was not associated with increased rates of death or relinquishment or occurrence of any serious medical or behavioral condition and may provide certain important long-term benefits, especially for male cats. Animal shelters can safely gonadectomize cats at a young age and veterinarians should consider recommending routine gonadectomy for client-owned cats before the traditional age of 6 to 8 months.”
It should be noted that similar focused studies have not been conducted to establish the long-term safety of gonadectomies performed at 6 months of age.
Obesity is influenced by a number of factors, and while neutered animals do have a tendency to weigh more than intact animals, it occurs regardless of whether the surgery was performed prepubertally or at the conventional age of six months. A published study in 1991 indicated that dogs did not develop obesity when they were sterilized at either pre or post puberty. Another study from 1996 showed that cats can gain weight after gonadectomy, but this is for both gonadectomy at the traditional age as well as prepubertal.
It should be stressed again that obesity is a multi-factorial problem. Even an intact animal can become obese if a proper diet and exercise regimen is not followed. Just as in humans, dietary indiscretions and lack of activity are the real culprits in this case.
Many veterinarians erroneously believe that pediatric spay/neuter will stunt the growth of animals. In fact, the exact opposite is true. This concern about stunted growth following prepubertal gonadectomy has been refuted by multiple studies.
In contrast to intact dogs, pups spayed or neutered at 7 weeks of age and male pups neutered at 7 months of age had greater final radius and ulna lengths. The removal of hormonal influences on the growth plates of the long bones results in delayed closure, resulting in bones that are actually a little longer. However, no clinical significance to this difference in size has been found.
In cats, although prepubertal gonadectomy had a similar effect of delayed closure of the growth plates, this did not lead to clinically significant differences in the final length of the long bones.
Cranial Cruciate Ligament Rupture
In humans, cranial cruciate rupture (CCL) is more common in women than men and may be more likely to occur during certain phases of the menstrual cycle, which may be due to a hormonal effect on joint stability (Root Kustritz). Reported incidence of rupture of the CCL in dogs is 1.8%, and this is reportedly more common in sterilized female and male dogs than in intact dogs (Root Kustritz).
The exact cause and effect relationship has not yet been defined, but in addition to the suspected hormonal influence, heredity, body weight, and body condition score may all play a role in CCL rupture (Root Kustritz). There have not been any studies that have shown that delayed closure of the growth plates of the long bones results in asynchrony and/or abnormalities in joint formation as a cause of CCL rupture in dogs.
Long term studies have looked at the incidence of hip dysplasia in dogs and the association of hip dysplasia with pediatric spay/neuter (Howe, personal communication). The reported incidence of hip dysplasia is 1.7% with an increased incidence in large and giant-breed dogs (Root Kustritz). In the long term Cornell study, puppies that underwent pediatric spay/neuter before 5.5 months of age had an increased incidence of hip dysplasia. However, an additional finding of this study was that dogs that were gonadectomized at the traditional age were three times more likely to be euthanized for the hip dysplasia as compared to the early gonadectomized group. The authors suggest that early age gonadectomy may be associated with a less severe form of hip dysplasia (Howe, personal communication).
The effects of pediatric spaying and neutering on behavior remain largely unknown. Sterilization and the subsequent decrease in related hormones have been correlated with a decrease in gender-specific behaviors. Neutering at any age reduces the urge of male animals to spray urine to mark territory, roam and fight with other male animals. The demonstration of sexual behaviors in male cats can make them undesirable house pets, and a decrease in such behaviors is a powerful benefit of having them neutered. Also, the trainability of working dogs is not altered by gonadectomy and does not vary with age of the dog at time of surgery (Root Kustritz).
The large Cornell study of dogs sterilized before 5.5 months of age indicates an increase in noise phobias and sexual behaviors and a decrease in escaping, separation anxiety, and urination in the house when frightened (Spain, Scarlett, Houpt, 2004). However, a different study showed no difference in the incidence of overall or specific behavioral problems between early-age and traditional-age sterilization (Howe, 2001).
There is some early evidence that animals that are gonadectomized at 7 weeks or 7 months of age are more active and excitable, and that male and female cats may be more affectionate than those left intact, but this is a fairly subjective observation that requires more research to substantiate. There does not appear to be any clinical significance to any observed behavioral differences.
Lower Urinary Tract Disease
Pediatric spay/neuter has not been found to contribute to a higher rate of urinary tract obstructions in male cats. Studies have been conducted on male cats to determine the incidence of urinary tract obstructions in all populations. It was found that the diameter of the penile urethra did not vary between animals neutered at 7 weeks or 7 months of age or from intact male cats.
It was originally believed that castrated cats had a higher incidence of urinary tract blockages, but this is not the case. The penis in male dogs castrated at 7 weeks of age is smaller as is the os penis, and preputial development is juvenile in comparison with dogs castrated at 7 months of age or left intact, but there has been no clinical significance attached to those differences.
Secondary Sexual Characteristics
The vulva of spayed females is smaller than that of intact bitches, but there is no evidence that there is any clinical significance to this size difference. Perivulvular dermatitis occurs in intact as well as spayed females, and is related to obesity rather than sexual status. Mammary glands and nipples are also smaller.
The penis and prepuce of male animals will retain a juvenile appearance, but again, there is no evidence of any clinical significance in animals that are not sexually active. There is a reduction in the male cat's ability to extrude the penis from the prepuce, but there is no knowledge of any clinical problems associated with this. It can occur whether the surgery is performed at 7 weeks or 7 months of age.
Urinary incontinence, or the inability to control urination, may be observed in female dogs whether they are spayed or intact, and regardless of the age when spayed. Older, intact female dogs may experience incontinence naturally as a result of the decrease in circulating estrogen, which has an effect on the external urethral sphincter. In spayed dogs, incontinence may be seen soon after the surgery has been performed, years later, or not at all.
The long-term Cornell study showed a slight increased risk of urinary incontinence for female dogs spayed before 12 weeks of age (12.9% vs. 5.0%). However, it is important to note that there was no incidence of relinquishing these dogs to the shelter; they remained in their homes. Also, the long-term study from Texas A&M that followed dogs out 4 years post surgery did not show an increased risk of urinary incontinence. Finally, another study from 1992 showed a higher incidence of urinary incontinence in female dogs spayed AFTER the first estrus cycle (20.1%).
It would appear that there is a need for more research, but practitioners who are concerned about this slightly increased risk of incontinence may still safely perform prepubertal puppy spays at 3-4 months of age. Many shelters continue to perform the procedures on puppies under 3 months of age because the study did not show an increased risk of relinquishment because of incontinence, which can be treated, and because of the high rate of failure to return for spaying when adopters are allowed to take intact female puppies home.
It is true that some shelters find an increased incidence of infectious disease (in particular, upper respiratory infections (URI) in cats and parvovirus in dogs) in animals that are neutered prepubertally, but the stress of anesthesia and surgery affects adult animals as well, not just kittens and puppies. One study showed that surgery and anesthesia have little effect on the dog's ability to mount a humoral antibody response to distemper vaccination. Many of these shelter animals might have developed disease anyway because of the presence of these infectious agents in shelters.
Good screening of surgical candidates, a comprehensive veterinary health care program that includes deworming, good nutrition, stress reduction, good sanitation, appropriately timed vaccinations, etc., and good post-operative care can minimize the impact of this problem.
Shelters that neuter animals only after they have been selected for adoption and send them home after the surgery to recuperate seem to have fewer problems with upper respiratory infections. Infectious disease should not be a problem in the private-practice clinical setting.
Hypothyroidism occurs more commonly in sterilized dogs than in intact dogs, but while there is an association, a direct cause and effect has not been established. The overall incidence of hypothyroidism in dogs is 0.2 to 0.3%. Certain breeds, such as Doberman Pinschers, Golden Retrievers, and Dachshunds, have a predilection for this disease.
In performing a risk-benefit analysis of pediatric neutering, it should be pointed out that the incidence of hypothyroidism is low, the condition is readily treatable, and most dogs have a good response to medical treatment. In addition, other diseases which can be prevented by gonadectomy (such as mammary neoplasia, pyometra, and prostatic hyperplasia) have much higher incidences and may not have as favorable an outcome as hypothyroidism.
Sterilized male and female cats have been shown to have an increased risk of developing diabetes mellitus than intact male and female cats (Root Kustritz). Other risk factors for cats in developing diabetes mellitus include breed (Burmese have a higher incidence), sex (males have a higher incidence), obesity, and increasing age (Root Kustritz). Recent new theories suggest a high-carbohydrate, dry-food diet may also be a contributing factor to the development of diabetes in cats.
There has been concern that pediatric spay/neuter may increase the risk for certain types of cancer. But, pediatric spay/neuter will also decrease the risk for other types of cancer. For example, mammary gland tumors are the most common type of tumor of female dogs, with a reported incidence of 3.4%. Mammary gland tumors are the third most common tumor of cats, with a reported incidence of 2.5% (Root Kustritz). Sexually intact dogs and cats have a much greater risk of developing mammary gland tumors than gonadectomized animals (Root Kustritz). The literature also shows that the risk of developing mammary gland tumors in dogs spayed prior to the first estrus is 0.5%, while the risk after the first estrus is 8.0%, and the risk after the second estrus increases to 26%.
Another type of neoplasia that may be affected by gonadectomy is prostatic neoplasia. While some studies show an increased risk of prostatic neoplasia in castrated dogs (Root Kustritz), the reported incidence of prostatic tumors in dogs is only 0.2% to 0.6% (Root Kustritz), and it occurs in both intact and castrated male dogs. So while castration does not protect against prostatic neoplasia, it does protect against other prostatic diseases seen more commonly in intact male dogs. These include benign prostatic hyperplasia (BPH), cystic hyperplasia, squamous metaplasia, paraprostatic cysts, prostatitis, and prostatic abscesses.
Another tumor associated with gonadectomy is hemangiosarcoma. Spayed females have 5 times the risk of developing cardiac hemangiosarcoma compared to intact females (Root Kustritz). However, the overall incidence of cardiac tumors in one study was only 0.19%, making them very uncommon compared to other tumor types.
Gonadectomy can increase the risk of development of osteosarcoma (OSA) by 1.3 to 2.0 times (Root Kustritz). In one study, there was a significant increase in OSA in sterilized dogs that had undergone gonadectomy at less than 1 year of age, but the overall incidence of OSA in this population of dogs (Rottweilers) was much higher than that in the general population, which suggests a hereditary component (Root Kustritz). Also, in this study, the life span of sexually intact and castrated male dogs did not differ, and the life span was actually increased in spayed female dogs compared to intact female dogs (Root Kustritz). This study also looked at dogs that underwent gonadectomy before 1 year of age, and this cannot be defined as pediatric spay/neuter (Howe, personal communication).
Transitional Cell Carcinoma (TCC) is the most common tumor of the urinary tract of dogs. Gonadectomized animals have an increased risk of developing TCC compared to sexually intact animals (Root Kustritz). However, a cause and effect relationship has not been defined, and TCC in dogs is reported to be at most 1.0% of all malignant tumors (Root Kustritz).
Testicular tumors are the second most common tumor type in dogs. Although malignancy is considered low for these types of tumors, castration is usually curative (Root Kustritz). Ovarian and uterine tumors are not common in dogs and cats, and although malignant tumors of the female reproductive tract have been reported, sterilization is usually curative (Root Kustritz).
The following pointers highlight the main considerations when performing a pediatric surgical procedure.
Pre-Surgical and Anesthetic Considerations
The handling of pediatric patients before surgery should be minimized to prevent excitement before sedation for surgery. The staff should be urged to resist the temptation to play with the puppies or kittens. Excited animals will resist being restrained, and they become more difficult to sedate. Littermates should be housed together to reduce stress.
Intramuscular or subcutaneous injections for initial sedation or pre-medication are recommended as less restraint is needed.
Animals should not be fasted for more than 3-4 hours before the procedure to avoid hypoglycemia.
Hypothermia can be a problem for these patients. A small area of hair at the surgical site should be clipped and a warm surgical scrub used. The use of alcohol should be avoided or minimized because of its cooling effects on the skin. Supplemental heating sources should be used as needed, such as circulating hot-water heating pads or carefully monitored warm-water bottles. (Avoid placing them directly on the skin, and remove them immediately when they become cool.)
There are many different protocols in the literature for pediatric anesthesia. The most successful protocols are usually already in use by the veterinarian with adjustments for the weight difference. The use of isoflurane inhalation anesthesia eliminates many of the concerns about biotransformation of anesthetic drugs in the liver and kidneys of pediatric patients. (Halothane should not be used on the pediatric patient.) The current recommendation is to use multimodal analgesia, such as nonsteroidal anti-inflammatory drugs (NSAIDS) in combination with opioids.
Good monitoring of the patient for safety is no different from the protocols used for any other patient. These include observing the heart and respiratory rates, depth of anesthesia, color of the patient's mucus membranes, etc.
A supplemental source of heat should be used to prevent hypothermia during the surgical procedure. Circulating warm water heating pads covered by a blanket or towel on the surgical table work well.
Some surgeons recommend that the surgical incision for spaying female puppies should be more caudal than the incision for female adult dogs. The location of the incision for spaying kittens remains the same as it is for adult cats, in the caudal third of the ventrum. Male puppies may be neutered through a scrotal incision, the same as male cats.
Tissues must be handled gently and close attention paid to hemostasis, but this is true in any surgical procedure. The truth is, in most cases, bleeding in these animals is minimal. Usually only single ligatures are indicated and hemoclips can also be used, compared to the adult patient where double ligation is often indicated.
Pediatric animals can have a significant amount of clear abdominal fluid, but this is normal.
The animals should be tattooed in the inguinal region, on the ventral abdomen or have tattoo ink applied to the incision to identify them as having already been neutered. Tattooing is as important for males as it is for females, as it might spare male animals from exploratory surgery if it was assumed the animal had bilaterally retained testicles.
Puppies and kittens should be kept warm in the post-operative period. Heating lamps can be used to prevent hypothermia as long as the patient is closely monitored while under the lamp. If there are problems with the recovery, their temperature and blood glucose should be checked.
A small meal should be offered within an hour after anesthetic recovery to minimize the chance of developing hypoglycemia. If there are signs of hypoglycemia, treat quickly and accordingly. Many practitioners recommend routinely applying a small amount of Nutrical on the gums of the recovering pediatric patient.
Some surgeons recommend avoiding the use of PDS suture material in the subcutaneous and subcuticular (intradermal) tissue, as there have been reports in the literature of PDS in these tissue layers being associated with the post-op complication of calcinosis circumscripta.
One of the main reasons why many veterinarians do not perform pediatric spay/neuter is that they are most comfortable performing surgery on animals that are 6 months of age or older, and they believe there are no compelling reasons to change the current protocols in their private practices. However, there are actually many advantages to pediatric spay/neuter. Although some have been mentioned before, they are summarized here:
As with all veterinary procedures, there are potential complications and both advantages and disadvantages to any spay/neuter procedure. Each patient should be evaluated on an individual basis and the veterinarian should discuss both the benefits and risks for spay/neuter surgery with the client. Pediatric spay/neuter is important for humane societies and shelters because with these procedures, almost every animal can be sterilized prior to adoption, which helps prevent the birth of unwanted litters that often end up at the shelter. Private practitioners should also consider performing pediatric spay/neuter on their patients because of the many medical advantages as well.
Lila Miller, DVM, is Vice President of ASPCA Veterinary Outreach.
Photo credit: PAWS puppies © Maggie Swanson