Spay and Neutering Information

In order to control the canine population boom (and to decrease the number of dogs destroyed each year), surgery should be performed early.


For decades, the standard in the veterinary profession was to spay female dogs and cats at the age of six months, and neuter males at nine months. This standard has contributed significantly to the tragedy of pet overpopulation, since most cats and many dogs have reached physiological sexual maturity by that time. Fortunately, the standard is changing.

Female dogs can come in season (and get pregnant) prior to age six months. A dog’s estrus cycle can be messy, leaving spots of blood on carpets and furniture, and a dog in heat can be a real nuisance. Every unsterilized male dog for miles around will make supercanine efforts to reach her. Packs of eager would-be lovers congregate in the street, fighting among themselves and threatening passers-by.

Having a fence adequate to keeping your female dog confined is not always sufficient to keep amorous suitors out. Determined male dogs have been known to scale tall fences in a single bound, tear boards off of fences with their bare paws, and even crash through plate glass windows to get to the objects of their desire. Even the most careful dog owner can be surprised 63 days later, when Virtuous Violet presents a litter of puppies sired by the athletic Adonis who managed to breach the back yard defenses and claim his prize while family members were all at work or at school.

Male dogs can reach sexual maturity and begin exhibiting unacceptable behaviors such as fighting and uncontrollable leg lifting well before nine months of age. Once Fido has started fighting with other male dogs you have a significant behavior problem on your hands; it can be very difficult, sometimes impossible, to convince him to stop.

Shelter statistics convincing
Twenty-five years ago, when I had just started working in the Customer Service Department at the Marin Humane Society in Novato, California, we sometimes took in as many as four to six litters of puppies on a single summer Saturday. We had nowhere near enough room for that many baby dogs – only a small percentage of them had the good fortune to eventually find homes. On the shelter forms that owners filled out when they gave up an animal was a blank for “Reason For Surrender.” All too often, the reason given was that “Violet got pregnant before we could get her spayed.”

Shelters have been working diligently for decades to solve the problem of pet overpopulation, promoting spay/neuter practices and responsible pet ownership in their communities, and requiring adopters to sign sterilization contracts as part of the adoption process (contracts that are notoriously difficult to enforce).

A 1987 survey conducted by the American Humane Association (AHA) concluded that less than 60 percent of adopted puppies and kittens were spayed or neutered after being adopted. Profoundly disturbed to realize that their own adoption programs were contributing to the overpopulation problem, many shelters redoubled their efforts to encourage compliance with their adoption contracts. A handful of shelters (including the one I worked for) succeeded in attaining compliance rates in the upper 90th percentile by committing significant staff and volunteer time and resources to pre-sterilization of dogs and cats six months and older, follow-up phone calls to adopters of puppies and kittens, citations for violations of local or state laws requiring sterilization of shelter adoptees, and “repossession” programs – the actual impoundment of animals for the purpose of spay/neuter surgery. (Most impounded animals were returned to their owners once the surgery was completed.)

Despite these aggressive programs, a 1993 survey from AHA found that many shelters still hovered in the 50-60 percent compliance range; an unacceptable failure rate of 40-50 percent, for shelters that were collectively euthanizing 10 to 12 million unwanted animals each year.

The surveys revealed, however, that a significant contributor to that high failure rate stemmed from the adoption of puppies and kittens who were too young to be sterilized prior to adoption. For a long time, however, a solution to that problem hovered on the horizon: lowering the accepted age of spay/neuter to seven to eight weeks. Drastic? Perhaps, from the conventional perspective. But the ongoing euthanasia of as many as 18 million companion animals a year called for drastic measures.

A historical perspective
Where did the tradition of six- and nine-month spay/neuters come from anyway? Not from any scientific basis, says Joan Freed, DVM, a free-lance veterinarian in the San Francisco Bay area whose specialty is prepubescent spay/neuter.

“In the 1930s and 1940s when the ages became standardized,” says Dr. Freed, “the spay ‘hook’ (a surgical tool that resembles a crochet hook and enables a veterinarian to more easily snag the elusive uterus) had not yet been invented, and it was difficult to find the uterine horn on a young kitten or puppy. After the first heat the uterus was enlarged and easier to find. Even after the spay hook was invented, tradition continued to dictate the accepted ages of six and nine months for sterilization of females and males, respectively.”

One theory was that if the animals didn’t reach sexual maturity prior to sterilization their growth would be stunted, and they could potentially suffer serious health and developmental problems (such as urinary blockages) due to the lack of hormones. This theory was never scientifically tested. In fact, studies conducted in the early 1990s proved just the opposite. Dr. Freed obtained her veterinary degree from the University of Florida College of Veterinary Medicine in 1982, and is a strong advocate of prepubescent sterilization. (Author note: I prefer the terms “pediatric,” “prepubescent” or “juvenile” spay/neuter to “early” spay/neuter, since “early” implies that we are doing it too soon. In fact, it is not “early” spay/neuter, it is “on-time” spay/neuter!) Dr. Freed has worked with animal shelters for almost a decade, beginning at Alachua County Animal Services in Gainesville, Florida in 1990. Her experiences with shelter animals headed for the euthanasia room have fueled her intensity as an advocate for juvenile spay/neuter.

“I’m so gung ho on it, it’s just obnoxious. But it’s so much easier on the animals,” she insists. “The surgery is so much easier.”

Some of the most significant research in the field of spay/neuter ages was conducted by two of her colleagues at the University of Florida, Mark Blomberg, DVM, and Kathy Salmari, DVM. Drs. Blomberg and Salmari conducted two separate studies, one with dogs, one with cats. The kittens and puppies were divided into three groups: those spayed or neutered at age seven weeks, seven months, and a control group that wasn’t sterilized. Results of the studies showed no differences in physiological or behavioral development between those animals sterilized at age seven weeks and those done at seven months. Of special significance was the finding that there was no difference in urethral pressure between any of the groups, implying that juvenile spay/neuter is not a contributing factor to urinary blockages.

There were some measurable physiological differences. The control group (intact) animals tended to weigh less than their sterilized counterparts, confirming conventional wisdom’s insistence that sterilized animals tend to “get fat.” (You can control this effect with relative ease by providing your sterilized dog with more exercise and/or fewer calories.) The growth plates in the legs of the sterilized animals closed later than those of the intact animals due to the absence of sex hormones that, among other things, promote growth plate closure. This means that the sterilized animals actually grow taller than their intact compadres, by an almost imperceptible few millimeters – the exact opposite result of the “stunted growth” fears.

Behavioral differences between neutered and unneutered male dogs are well known. Intact males are far more likely to roam, fight, (and risk injury and exposure to diseases such as parvovirus and distemper, not to mention impoundment by animal control), lift their legs obsessively, and bite than are their neutered brothers. Neutering earlier, rather than later, is likely to forestall unacceptable behaviors that can be extremely difficult to resolve once they are established.

Anecdotal evidence
The concept of prepubescent spay/neuter first came to the attention of much of the animal protection world when Leo L. Lieberman, DVM, published an article promoting the practice in the September, 1987 issue of the Journal of the American Veterinary Medical Associationm (JAVMA). According to the article, several shelters had been performing juvenile spay/neuter for quite some time.

The SPCA in Medford, Oregon, reportedly sterilized 8,000 puppies and kittens at 6 to 12 weeks of age from 1974 through 1980, without any adverse effects reported by their owners. During this period the shelter documented a 68 percent decrease in euthanasia, from 14,332 animals in 1973, to 9,750 in 1979. The Vancouver, BC SPCA began doing juvenile spay/neuter as early as 1976, and the municipal animal shelter in Memphis, Tennessee, began a similar program in 1987 following the publication of Lieberman’s article.

In February of 1988, Cornell University’s College of Veterinary Medicine Animal Health Newsletter supported Lieberman’s position. Citing the static figures of animal euthanasia in animal shelters, the newsletter’s cover story stated ” . . . it might be well for animal lovers to get behind the trend toward early neutering.” The ball was rolling. Pediatric spay/neuter became a hot topic at national animal protection conferences, and more and more shelters began lowering the age at which they sterilized their adoption animals.

The bandwagon rolls forward
A 1992 study conducted by the Massachusetts SPCA found that while 73 percent and 87 percent, respectively, of all dogs and cats in homes had been neutered, 20 percent of all neutered animals had been allowed to reproduce prior to neutering – a practice that definitely contributes to the overpopulation problem.

In 1992, AHA issued a policy statement in strong support of prepubescent spay/neuter, reassuring shelters that were fence-sitting on the issue. The number of shelters performing sterilization of young kittens and puppies began to steadily increase. That same year, the July-August issue of Pet Veterinarian published the results of a non-scientific survey they had conducted, indicating that 65 percent of their veterinarian readers believed that pediatric neutering was a good idea for animal shelters, and that 40 percent of veterinary readers had themselves performed sterilization surgery on animals 6 to 12 weeks of age. Even private veterinarians were climbing on the pediatric spay/neuter bandwagon.

The January 1993 issue of California Veterinarian focused on “early” spay/neuter, with articles that overwhelmingly supported the practice – including one from the prestigious UC Davis Department of Veterinary Surgery proposing a prepubertal spay/neuter program at the Davis Veterinary School. In 1999, the American Veterinary Medical Association (AVMA ) finally caught the pediatric spay/neuter train, and passed a resolution and issued a public position statement supporting prepubertal spay/neuter.

Best for your dog?
It’s all well and good to agree that pediatric spay/neuter is an important part of the solution to the pet overpopulation problem. It’s something else entirely to look at the bright ball of fur pushing her Buster Cube around your living room, and imagine her sliced open on the surgery table. Isn’t surgery incredibly stressful on such tiny babies?

“There are some concerns that are easily addressed with changes in protocols,” says Dr. Freed. “In general, however, prepubertal surgery is much easier on the animals. They heal much more quickly because they are in a rapid stage of growth. When we neuter a male puppy we can’t even see the incision eight hours later. Kittens and puppies wake up after surgery, bouncing, eating and playing with an abundance of energy, as if nothing even happened. Older animals are still groggy hours after the babies are fully recovered.” (Note: Dogs who are spayed at age six months or later generally have visible or palpable spay scars for the remainder of their lives, so a vet can usually tell if a dog has already been spayed. Many veterinarians now tattoo a tiny dot or letter “S” on a female puppy’s abdomen during surgery since the spay scar will not be visible when she grows up.)

“There are three things to be aware of,” Dr. Freed continues. “Babies can’t regulate their body temperature well, until around the age of four months. Prior to that we must help them maintain their body temperatures or they can become hypothermic. We need to surgically prep and moisten the smallest area possible, and during recovery use a warm water blanket or Thermal BarrierTM heating pad type product designed for animal surgeries.”

The second medical consideration, says Freed, has to do with the overnight fast that veterinarians typically require before surgery. “Kittens and puppies are also at risk for hypoglycemia, so we don’t fast them overnight like we do with adults. They can eat up to an hour before surgery, and again as soon as they are fully awake.”

The third concern is for a young animal’s less-developed immune system being challenged by the stress of surgery. For shelter animals, this is in addition to the considerable stress created by the shelter environment itself.

“I am aware that some other shelter vets have reported problems with disease following surgeries,” says Dr. Freed, “but this has not been my experience. Naturally, we must adhere to common sense sterile surgical procedures. When I neuter two puppies from a litter of five and the neutered puppies break with kennel cough, invariably so do the three puppies who did not undergo surgery. The sterilized puppies seem to have no more difficulty recovering from the URI than do their unsterilized littermates.” Bottom line? “I have spayed and neutered some 7,000 puppies,” Dr. Freed continues, “and not had one serious post-surgical problem. Not one.”

Breeders should neuter early
Pediatric spay/neuter is not just for shelter puppies. It is also the perfect solution for dog breeders, who have previously had no real control over whether their “pet quality” pups were actually sterilized. A responsible breeder requires spaying and neutering in the sales contract when selling a pet puppy, but, like shelter adoption contracts, these are extremely difficult to enforce. By having puppies spayed and neutered before selling them, a breeder can know for certain that none of her dogs’ offspring will contribute to the pet overpopulation tragedy.

There is no question that responsible dog owners will spay and neuter their pets. The only question is “When?”

When arguing for pediatric spay/neuter, Dr. Freed answers that question with a question of her own: “Of course you are going to sterilize – the sooner the better. Why make it any more difficult on your dog?”

-By Pat Miller

Author Pat Miller, CBCC-KA, CPDT-KA, is WDJ’s Training Editor. She and her husband Paul live in Fairplay, Maryland, site of her Peaceable Paws training center, where Pat offers dog-training classes and courses for trainers.

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Pat Miller, CBCC-KA, CPDT-KA, grew up in a family that was blessed with lots of animal companions: dogs, cats, horses, rabbits, goats, and more, and has maintained that model ever since. She spent the first 20 years of her professional life working at the Marin Humane Society in Marin County, California, for most of that time as a humane officer and director of operations. She continually studied the art and science of dog training and behavior during that time, and in 1996, left MHS to start her own training and behavior business, Peaceable Paws. Pat has earned a number of titles from various training organizations, including Certified Behavior Consultant Canine-Knowledge Assessed (CBCC-KA) and Certified Professional Dog Trainer - Knowledge Assessed (CPDT-KA). She also founded Peaceable Paws Academies for teaching and credentialing dog training and behavior professionals, who can earn "Pat Miller Certified Trainer" certifications. She and her husband Paul and an ever-changing number of dogs, horses, and other animal companions live on their 80-acre farm in Fairplay, Maryland.


  1. Early spay and neutering is being questioned by a number or reliable sources. Problems develop such as growth plates not being signaled to close, dog genitals do not fully develop, and a host of other issues. Read the pros and cons on early neutering before you ever consent to it.

  2. This is horrendous advice! I implore individuals to seek a more centered article on making this decision; one that should not be taken lightly. The benefits to delayed spays, ovary-sparing spays, vasectomies, etc are overwhelming! So many musculoskeletal, endocrine, urogenital + issues are arising and directly associated with EARLY spay – call it what it is don’t throw euphemisms at it.