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Early Neutering: We’ll Call This Myth Busted…

Story at-a-glance
  • Spaying female dogs at a young age, especially before their first estrus cycle, has long been hailed as a method of eliminating or reducing the risk of mammary neoplasia (breast cancer). In fact, most animal welfare organizations and veterinarians are quick to list breast cancer prevention as one of the many benefits of early spaying.
  • But what is the science behind this assertion? As it turns out … there isn’t much. A study conducted by the Royal Veterinary College in the U.K. points to a lack of hard evidence of a link between spaying/early spaying and a reduction in mammary tumors in female dogs.
  • The U.K. study was a systematic review based on internationally recognized Cochrane Review guidelines used in human medicine. The results of the systematic review point to the need for similar high-quality research in veterinary medicine.
  • Pet owners are entitled to know the risks and benefits of any procedure performed on their furry charges. In this instance, a widely promoted benefit of spaying/early spaying may not offer the level protection from breast cancer dog owners have been led to believe.
  • Spay/neuter decisions by individual pet owners should be based on a holistic approach to the animal’s health and quality of life.

Early Spaying

By Dr. Becker

If you Google the term “benefits of spaying,” you’ll get tens of thousands of results, many of which list protection against mammary neoplasia (breast cancer) as a benefit of early spaying of female dogs.

In fact, according to well-known resource Petfinder.com1:

“Spaying before the first heat virtually eliminates the development of breast cancer later in life for both dogs and cats. (If the surgery is performed when the animal is older, this benefit will be lost.)”

And the ASPCA2 says this:

“Females spayed prior to their first estrus cycle have a significantly reduced risk of developing mammary cancer, a common cancer in unspayed females. The chances of developing this cancer increase if a female isn’t spayed until after her second heat cycle, but they still remain lower than the risk for unspayed females. So if your dog has already gone through her first heat cycle, it’s not too late. Spaying her will still reduce her risk of developing cancerous mammary tumors.”

According to Clinician’s Brief, a majority of veterinarians recommend spaying, and about 16 percent encourage performing the procedure before the first estrus cycle in order to receive the alleged added benefit of protection against mammary tumors.

Under the circumstances, it would seem there must be ample scientific evidence that spayed female dogs, and especially those spayed before their first estrus cycle, have less incidence of breast cancer … right?

Not So Fast … What Evidence Supports the Link Between Spaying and Reduction in Mammary Tumors?

Results of a study published last year in the Journal of Small Animal Practice3 were unable to validate the theory – a theory that is widely assumed to be a fact – that early spaying protects female dogs from mammary neoplasia.

The study was a systematic review conducted by members of the Veterinary Epidemiology and Public Health Group of the Royal Veterinary College in the U.K. A systematic review is an examination of several studies for the purpose of summing up the best available research on a particular subject. For the study, peer-reviewed analytic journal articles in English were eligible and were assessed for risk of bias by two reviewers independently.

The objective of the study was to evaluate the quantity and veracity of evidence that spaying, or the age at which a dog is spayed, has an effect on the risk of mammary tumors.

There were over 11,000 search results on the subject, of which 13 were English-language, peer-reviewed reports focused on the link between spaying/age of spay and mammary tumors. Of those 13, nine were deemed to have a high risk of bias, and the remaining four had a moderate risk of bias. (For more information on how bias was assessed and how the researchers screened the results, the full study can be found here.)

Of the four moderate-risk-of-bias studies, one found a link between spaying and a reduced risk of mammary tumors, two found no evidence of a link, and one suggested “some protective effect,” but no specific details were offered.

The Royal Veterinary College reviewers concluded that:

“Due to the limited evidence available and the risk of bias in the published results, the evidence that neutering reduces the risk of mammary neoplasia, and the evidence that age at neutering has an effect, are judged to be weak and are not a sound basis for firm recommendations.”

Simple translation: the idea that spaying, and early spaying of a female dog before her first estrus cycle, removes or reduces her risk of breast cancer is at the present time a theory rather than a fact.

The methodology used in the U.K. study was based on Cochrane Review guidelines, which are internationally recognized for their high standards in evidence-based medicine for humans. According to Dr. Ann Hohenhaus, a veterinary oncologist, results of this study highlight the need for quality research in veterinary medicine. Dr. Hohenhaus goes on to say:

“Despite lack of evidence found to support early spaying as preventing mammary tumors, veterinarians may continue to recommend it to prevent estrus cycles, unwanted litters, and pyometra. Clinical experience may suggest that early spaying decreases the risk of mammary tumors, but without additional well-designed trials, scientific evidence to support this is lacking.”

Spay/Neuter Decisions Should Be Based on Your Pet’s Health and Quality of Life

For the record, I’m not advocating leaving female dogs intact indefinitely, nor am I suggesting dogs should not under any circumstances be spayed or neutered at a young age.

My goal with regard to pet sterilization is simply to provide information to pet owners about the risks, since there is much information readily available about the benefits. In this case, where early spaying has been widely promoted as a way to prevent mammary tumors in female dogs, in light of the findings of the U.K. systematic review, I feel compelled to let pet owners know there is scarce scientific evidence available to back up that widely held belief.

If your dog is not yet spayed or neutered, I can offer some general recommendations for timing of the procedure:

  • Your dog should be old enough to be a balanced individual both physically and mentally. For the majority of dogs, this balance isn’t achieved until a dog has reached at least one year of age. Although some breeds reach maturity faster than others, many giant breed dogs are still developing at two years of age.
  • Other considerations include your dog’s diet, level of exercise, behavioral habits, previous physical or emotional trauma, existing health concerns, and overall lifestyle. If your pet is emotionally balanced (has no behavior problems) consider investigating a vasectomy or tubal ligation instead.
  • I encourage you to learn all you can about surgical sterilization options and the risks and benefits associated with each procedure.

Related:

Part 2 of Dr. Becker’s Interview with Bestselling Author Ted Kerasote: The Seven Factors that Determine How Long Your Dog Will Live

Urinary and Fecal Incontinence in Pets

An Alternative to Surgery to Sterilize Male Dogs

New methods of pet ‘pampering’ include fake testicles and facials

Pet Sterilization Laws Raise Health Concerns

Caring for Pets Before, During and After Anesthesia

April 11, 2013 Posted by | Animal or Pet Related Stories, Animal Related Education, Dogs, Dogs, Just One More Pet, Pet Health, Pets, responsible pet ownership | , , , , , | 5 Comments

An Alternative to Surgery to Sterilize Male Dogs

Story at-a-glance

sterilized-dog

  • An injectable chemical sterilization drug will be available for use in the U.S. by the end of this year. It is currently FDA-approved only for dogs from 3 to 10 months, but the manufacturer believes it will be approved as safe for all dogs 3 months and older by the time it is released.
  • The drug, brand name Zeuterin, contains zinc gluconate neutralized by arginine. It acts as a spermicide and causes irreversible fibrosis of the testicles, which eventually atrophy and shrink in size, but remain visible.
  • Upon its initial release, Zeuterin will be made available primarily to shelters and spay-neuter clinics. The drug can only be sold to licensed veterinarians who have been trained in the injection procedure by the manufacturer.
  • The drug is highly effective at sterilizing male dogs with a single injection in each testicle. There are some side effects which seem primarily related to the injection technique.
  • It’s important to understand no sterilization procedure is completely risk-free, short or long-term. Once Zeuterin is widely available to private veterinary practitioners, we encourage dog owners to discuss with their vet the pros and cons of the procedure vs. traditional spaying or neutering.

By Dr. Becker

An injectable sterilization product for male dogs containing zinc gluconate neutralized with arginine is scheduled for release in the U.S. by the end of this year under the brand name Zeuterin ("zinc neutering"). The product is already in use in Bolivia, Columbia, Mexico and Panama under another name.

The drug is effective for permanent sterilization of male dogs at least three months of age. Zeuterin has been approved by the FDA for use in dogs three to ten months of age and can be obtained only by licensed veterinarians who have received training from the drug’s manufacturer, Ark Sciences, in how to perform the injections. The manufacturer believes the drug will be approved for use in dogs of any age over three months before the U.S. release date.

The drug functions as a spermicide and causes irreversible fibrosis of the testicles, which eventually atrophy and shrink in size, but remain visible. Dogs receiving the injection are tattooed in the groin area as proof they are sterile.

Product Launch Aimed at Shelters and Spay-Neuter Clinics Across the U.S.

Many shelters and spay-neuter facilities don’t have the recovery space for animals after sterilization surgery. For those organizations, Zeuterin should save time, money and space.

The injections are done on an outpatient basis, no anesthesia is involved, and dogs can be released relatively quickly after the procedure. Shelters and spay-neuter programs can then transfer some of the resources formerly committed to neutering male dogs toward spaying females and other outreach programs.

Proponents of Zeuterin believe it is unlikely individual veterinary practitioners will immediately embrace the sterilization drug, simply because they are already equipped and trained to do surgical spays and neuters. In addition, at this time Ark Sciences is training only a limited number of private veterinarians to inject Zeuterin.

Pet owners who want to have their male puppy chemically sterilized can add their names to a waiting list, which will at some point trigger Ark Sciences to send an offer to their vet to get certified to inject Zeuterin. According to Ark Sciences, the waiting list will be worked on a first-come first-served basis when the product becomes available.

It’s impossible to predict when Zeuterin might be widely available as an option for private vet practices and individual pet owners. Whenever that time comes, I think it’s important to understand the potential risks and benefits of this method of sterilizing male dogs.

Technology Approved by FDA in 2003

The formulation of zinc gluconate neutralized by arginine was actually approved by the FDA in 20031. That same year the drug was produced by Pet Healthcare International and distributed in the U.S. by Addison Laboratories under the name Neutersol.

According to Ark Sciences, Addison Labs overestimated the demand for the drug and created too much inventory. Excess inventory expired in two years, Pet Healthcare International went unpaid, and production shut down. Addison Labs and Pet Healthcare ended their relationship in 2005.

Ark Sciences subsequently acquired all rights to the Neutersol technology and has been distributing the product in Mexico and three other countries under the name Esterilsol for the last four years. They have used the drug extensively in Mexico in dogs three months and older to further evaluate its effectiveness as a sterilization agent, as well as to refine and improve the injection technique.

How the Drug Works as a Sterilization Agent

According to the Alliance for Contraception in Cats and Dogs (ACC&D) in their April 2012 Product Profile and Position Paper2 on Zeuterin:

As with any medical intervention, safety and effectiveness depend upon proper administration. The exact mechanism of action is not known. The following is based on a description provided by Ark Sciences. The product should be administered as an intratesticular injection into the center of the testicle via the dorsal cranial portion of testicle, parallel to the longitudinal axis. After injection the compound diffuses in all directions from the center of the testis. In the concentration used, zinc gluconate acts as a spermicide and destroys spermatozoa in all stages of development and maturation. It results in permanent and irreversible fibrosis in the seminiferous tubules, rete testis and epididymis. This produces a reduction in the size and texture of the testicles and permanent sterilization. Testosterone production is reduced by 41-52%, and the endocrine feedback system remains intact. Zinc gluconate is absorbed and metabolized by the body within 72 hours after the injection.

Also, from the Ark Sciences FAQ web page3:

How is testosterone lowered by Zinc Gluconate neutralized with Arginine?

The dosage and concentration is designed to ensure Leydig Cells in the interstitial space of the testes survive the procedure. Stimulated by Luteinizing Hormone (LH) produced in the pituitary gland, the Leydig Cells continue to support testosterone-related metabolic activity and growth. In the absence of spermatogenesis, Sertoli cells stop communicating the need for testosterone to mature sperm cells. The pituitary gland detects this lowered demand and lowers the LH levels. Since LH levels determine how much testosterone is produced by the Leydig cells, overall testosterone levels are reduced by 41-52% for all dogs permanently.

Zeuterin Adverse Reactions

The 2003 FDA drug approval document includes a study of 270 male puppies injected with the chemical sterilant. The puppies were a combination of shelter animals and family pets.

The following reactions were noted:

Reactions Upon Injection
Local Reactions

Reaction
Dogs Affected
Reaction
Dogs Affected

Vocalization
6
Scrotal Pain
17

Kicking
1
Scrotal Irritation
3

Biting and Licking
2

General Reactions
Scrotal Swelling
2

Reaction
Dogs Affected
Scrotal Dermatitis
2

Leukocytosis
2
Scrotal Ulceration
1

Neutrophilia
17
Scrotal Infection
1

Vomiting
12
Dry Scrotal Skin
1

Anorexia
11
Scrotal Bruising
1

Lethargy
6
Preputial Swelling
1

Diarrhea
5
Scrotal Sore
1

Another zinc gluconate sterilization study was done in the Galápagos Islands and published in 2008. It was conducted in a cooperative effort by the University of Florida, the ASPCA, and Animal Balance of San Francisco, and titled "Comparison of intratesticular injection of zinc gluconate versus surgical castration to sterilize male dogs."4 The following observation was made by the researchers:

Although the complication rate was similar for surgical and zinc-gluconate castration, the zinc-gluconate reactions were more severe. Surgical wound complications were treated by superficial wound debridement and resuturing. In contrast, zinc-gluconate reactions required antimicrobial treatment, orchiectomy, and extensive surgical debridement and reconstruction, including scrotal ablation in 2 dogs. These reactions occurred following administration by both experienced and novice individuals. All dogs made a full recovery following treatment of zinc-gluconate reactions and incisional dehiscences.

The authors of this study determined that proper injection technique is critical because injection or leakage into surrounding tissues can result in severe tissue damage. And while scrotal swelling and tenderness are common in the first days after injection, a more serious reaction is the development of scrotal ulcers or draining tracts in the scrotal or preputial area. The self-trauma that follows can be severe.

The researchers also observed that lesions aren’t always restricted to the injection site, which could indicate the solution may spread beyond the target area.

Long-Term Side Effects

According to Ark Sciences, since 1999 when the initial clinical studies were performed, there have been no reports of long-term side effects.

I would just add here that whenever we manipulate nature sufficiently to stop procreation, there WILL be long-term side effects. This is true for spay/neuter, and any other method. We are just beginning to understand the lifelong implications of surgical removal of ovaries and testicles, yet spaying and neutering of cats and dogs has been a common practice for decades.

I’m certainly not against the sterilization of pets. I’m a proponent of assessing the risks and benefits of everything we do as guardians of the animals in our care.

You can read more about Zeuterin on the Ark Sciences FAQ page as well as the other documents linked in the references, below.

Once the product is widely available to private veterinary practitioners, if you’re considering it, I recommend talking with your vet about the pros and cons of the procedure for your own dog.

Related:

Pet Sterilization Laws Raise Health Concerns

Caring for Pets Before, During and After Anesthesia

New methods of pet ‘pampering’ include fake testicles and facials

August 17, 2012 Posted by | Adopt Just One More Pet, Animal or Pet Related Stories, Animal Related Education, Dogs, Dogs, If Animlas Could Talk..., Just One More Pet, Man's Best Friend, Pet Friendship and Love, Pet Health, Pets, responsible pet ownership | , , , , , , , , , , , , | 4 Comments