Physical Effects of Spay

HAHD_SpayIn the healthcare and scientific communities, systematic reviews are utilized to guide medical decisions as they provide an exhaustive summary of high-quality peer-reviewed studies relevant to a research question. The foundation for our segments which outline the positive and negative effects of spay/neuter is a 2007 summary of a systematic review of more than 50 peer reviewed studies 83 in the veterinary medical literature with respect to the long term physical risks and benefits associated with spay/neuter in dogs. Since 2007, there have been significant studies performed which have expanded the knowledge base. We will include the results of these new studies as well. Most significant of the new studies is the 2012 meta-analysis of published studies 72 which concludes:

“A commonly-stated advantage of …[spaying] bitches is a significant reduction in the risk of mammary tumours, however the evidence for this has not previously been assessed by systematic review… Due to the limited evidence available and the risk of bias in the published results, the evidence that …[spaying] reduces the risk of mammary neoplasia, and the evidence that age at …[spaying] has an effect, are judged to be weak and are not a sound basis for firm recommendations.”

We would suggest with respect to the concern regarding mammary tumors in dogs not spayed, it would be prudent to provide annual or semi-annual mammary exams of these dogs to screen for mammary tumors, just as we do for humans.

On the positive side, spaying female dogs:

  • if done before 2.5 years of age, greatly reduces the risk of mammary tumors, the most common malignant tumors in female dogs 
  • nearly eliminates the risk of pyometra, which otherwise would affect about 23% of intact female dogs; pyometra kills about 1% of intact female dogs 44,45
  • reduces the risk of perianal fistulas 46
  • removes the very small risk (0.5%) from uterine, cervical, and ovarian tumors 21,22

HAHD_TPLO_SurgeryOn the negative side, spaying female dogs:

As a footnote to this discussion, we want to point out that conventional spay surgeries are invasive procedures, and involve removal of the ovaries and uterus. Multiple studies show that the total complications (intraoperative and postoperative) for spay surgeries are consistently about 20%.1,2,3,4  Further, the positive outcome listed above (nearly eliminates the risk of pyometra) is qualified because it is not uncommon for surgeons to inadvertently leave some portion of the uterus behind. The “stump” (of uterine tissue) as it is termed by veterinarians, is very susceptible to pyometra. For a more in-depth analysis of the complications of spay surgery please see our page with the same title.

Alternative sterilization procedures would be ovary sparing spay (hysterectomy) and tubal ligation. Both of these procedures are generally considered to be hormone sparing as the ovaries are left intact. However, new evidence seems to indicate removal of the uterus in ovary sparing spay (hysterectomy) does alter the hormone balance, whereas tubal ligation is truly hormone-sparing. Therefore, tubal ligation would be our choice over ovary sparing spay, but both procedures could be expected to have fewer complications as they are much less invasive procedures.