Summary

Canine sterilization is a set of commonly undertaken procedures designed to render a dog or bitch (male or female canine) incapable of reproduction. These procedures made their way into the veterinary lexicon after the issue of canine overpopulation raised concern from an increasingly pet-minded culture.

Since its inception, sterilization has been a controversial subject fraught with much debate over issues such as animal welfare and resource allocation. Is it necessary? Is it cruel? Is it worth the many millions of dollars it might cost to sterilize a nation’s “unwanted” animals?

The fact that sterilization could reduce certain unwanted canine behaviors and mitigate health risks helped establish it as a routine part of dog-keeping in the US and many other Western nations.

Many years after becoming commonplace in both public and private veterinary settings, the subject is still under debate. Questions about ideal sterilization methods and timing still play a starring role in the politics of pet-keeping and veterinary medicine in general.

The Basics

In the United States, sterilization is typically performed on dogs at the time of puberty, before the first “heat” cycle in females and before many of the undesirable male behaviors appear. Because canine puberty happens between 6 and 18 months of age, sterilization is generally undertaken at the 6-month mark in most private veterinary settings.

Female Sterilization

Procedures

Female dogs are typically sterilized in one of two surgical ways, both of them colloquially referred to as a “spay” procedure:

  • Ovariohysterectomy: This procedure involves the removal of the ovaries and the uterus. It is the most commonly performed female canine sterilization procedure in the US.
  • Ovariectomy: This is the most commonly performed female canine sterilization procedure in the EU. It involves the removal of the ovaries themselves.

Both of these procedures reduce a female dog’s reproductive hormone production; as a result, behavioral changes may occur and health benefits may be conferred.

Behavioral Changes

Very few behavioral changes have been consistently associated with a reduction in female reproductive hormone levels in dogs.

Health Benefits

Apart from the inability to procreate and the consequent elimination of diseases directly associated with reproduction, the most common health benefits associated with a reduction in female reproductive hormone levels in dogs include the following:

  • Eliminated or reduced potential for mammary tumors
  • Eliminated or reduced potential for pyometra (uterine infections)

Note: Tubal ligation in female dogs is not currently accepted as a form of sterilization because it doesn’t confer any of the health benefits of traditional spaying procedures. As with humans, it is, however, surgically feasible and may become more popular in years to come as more is understood about the health-related benefits and shortfalls of traditional female sterilization. Tubal ligation is not considered reversible in dogs.

Male Sterilization

Procedures

Though castration is by far the most commonly performed form of male canine sterilization, several procedures are currently undertaken in the male dog:

  • Castration: The surgical procedure known as castration, or “neutering” involves removal of the male reproductive hormone-producing gonads known as the testes or testicles. The procedure may or may not involve the removal of the scrotum as well. The more common version leaves the scrotum intact.
  • Zeuterin®: An injection of this solution into the center of each testicle renders a dog sterile in a relatively painless way. Sedation may be employed to keep dogs still, but is not strictly required. Some male reproductive hormones remain after the procedure, however, so while it is an effective means of sterilization, it’s unknown to what extent this method affects behavioral changes or confers health benefits.
  • Vasectomy: Though still considered a rare method of sterilization, this simple surgical procedure is effective. It requires the removal of a short segment from each of the two tubular structures known as the vas deferens. Severing these conduits for sperm effectively renders dogs sterile while preserving their ability to produce male reproductive hormones.

Behavioral Changes

The most common behavioral changes associated with a reduction in male reproductive hormone levels in dogs may include one or more of the following:

  • Decreased roaming
  • Decreased aggression
  • Decreased interest in females in heat
  • Decreased male reproductive behaviors (such as mounting and humping)
  • Decreased urine marking

Health Benefits

The most commonly cited health benefits associated with castration and/or a reduction in male reproductive hormone levels in dogs include the following:

  • Eliminated or decreased potential for testicular tumors
  • Eliminated or decreased potential for perineal hernias
  • Eliminated or decreased potential for certain prostatic diseases

Controversy

In recent years, controversy surrounding canine sterilization has complicated the once-simple issue over whether to spay and neuter dogs or not and when to perform these procedures.

While spaying and neutering at 6 months (around the time of puberty) was once seen as a matter of course, some veterinarians have begun to prevaricate on the ideal timing and even the necessity for sterilization in all cases.

Though most veterinarians agree that the majority of pet dogs should still be spayed and neutered at puberty, early sterilization (as early as 6 weeks of age) is commonly undertaken in shelter settings as a means of mitigating the pet overpopulation problem. This protocol is perceived by the shelter community as safe, effective, and humane as well as less resource intensive, but is not uniformly embraced by the larger veterinary community.

What’s more, some researchers have recently identified certain health conditions that may be more prevalent among dogs sterilized at or before the traditional age of 6 months. These initial findings raise some legitimate health concerns. Consequently, some veterinarians are beginning to consider a later date for sterilization — especially in those breeds these studies have specifically evaluated.

Until more definitive evidence exists to support delaying spays and neuters in certain cases, however, the veterinary community remains generally supportive of sterilization at or before 6 months of age for all non-breeding dogs.

References

Howe LM, Olson PN. Prepubertal gonadectomy in dogs and cats. I. Compendium on Continuing Education for the Practicing Veterinarian 21(2): 103-111, 176. ISSN: 0193-1903

S. Arnold, I. Reichler and M. Hubler. Urinary Incontinence in the Dog: Clinical Workup and Differential Diagnosis - [PDF](Last Updated: 21-May-06)

Merck Veterinary Manual. Principles of Therapy of the Reproductive System

Root Kustritz MV. Effects of surgical sterilization on canine and feline health and on society. Reprod Domest Anim. 2012. Aug;47 Suppl 4:214-22. doi: 10.1111/j.1439-0531.2012.02078.x.

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