Propaganda must not serve the truth especially not insofar as it
might bring out something favorable for the opponent.
~Adolf Hitler

Risks and Benefits of Spay and Neuter in Dogs

For decades in the United States, we have been led to believe that the only reponsible option for pet owners is to sterilize their dogs and cats, and the earlier the better. Six months of age has long been the standard, although in the last several years pediatric gonadectomies have become common on puppies and kittens as young as six weeks of age. In 2007, however, two articles were published that questioned this assertion, and pointed out some very real long-term health risks to sterilizing dogs and cats, especially at young ages. Since that time, the wool has been lifted from many of our eyes, and we have learned that there are, in fact, reasons to postpone spay and neuter, or to avoid it entirely.

The two articles that have sparked debate and a change in thinking regarding sterilization are these:

Long-Term Health Risks and Benefits Associated with Spay/Neuter in Dogs by Laura Sanborn, M.S.
Published May 14, 2007

Ms. Sanborn reviewed 55 studies and resources and presented both the benefits and risks of the surgeries for both sexes:

On the positive side, neutering male dogs

• eliminates the small risk (probably <1%) of dying from testicular cancer
• reduces the risk of non-cancerous prostate disorders
• reduces the risk of perianal fistulas
• may possibly reduce the risk of diabetes (data inconclusive)

On the negative side, neutering male dogs

• if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in medium/large and larger breeds with a poor prognosis.
• increases the risk of cardiac hemangiosarcoma by a factor of 1.6
• triples the risk of hypothyroidism
• increases the risk of progressive geriatric cognitive impairment
• triples the risk of obesity, a common health problem in dogs with many associated health problems
• quadruples the small risk (<0.6%) of prostate cancer
• doubles the small risk (<1%) of urinary tract cancers
• increases the risk of orthopedic disorders
• increases the risk of adverse reactions to vaccinations

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
• reduces the risk of perianal fistulas
• removes the very small risk (.0.5%) from uterine, cervical, and ovarian tumors

On the negative side, spaying female dogs

• if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common cancer in larger breeds with a poor prognosis
• increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by a factor of >5; this is a common cancer and major cause of death in some breeds
• triples the risk of hypothyroidism
• increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many associated health problems
• causes urinary "spay incontinence" in 4-20% of female dogs
• increases the risk of persistent or recurring urinary tract infections by a factor of 3-4
• increases the risk of recessed vulva, vaginal dermatitis, and vaginitis, especially for female dogs spayed before puberty
• doubles the small risk (<1%) of urinary tract tumors
• increases the risk of orthopedic disorders
• increases the risk of adverse reactions to vaccinations

The other ground-breaking article is:

Determining the optimal age for gonadectomy of dogs and cats by Margaret V. Root Kustritz, DVM, PhD, DACT
Published in the December 1, 2007 issue of the Journal of the American Veterinary Association.

Dr. Root Kustritz reviewed 182 studies and resources and concluded that:

"The veterinary profession recognizes the need for individual assessment of risk and benefit when evaluating vaccination protocols for animals. Elucidation of the genome in various species may lead to individualized diagnostic and treatment plans for each animal in the future. It behooves us as veterinarians dedicated to the provision of the best possible care for animals to educate clients and evaluate each animal carefully when making recommendations regarding gonadectomy."

References for Dr. Root Kustritz' studies may be added at a later date; until then, most are available via a search at PubMed.

Since those papers were published, a long-term retrospective study of female Rottweillers was completed which led to this conclusion:

In summary, we found female Rottweilers who kept their ovaries for at least 6 years were 4.6 times more likely to reach exceptional longevity (i.e. live >30 % longer than average) than females with the shortest ovary exposure. Our results support the notion that how long females keep their ovaries determines how long they live.

The full study is here:

Exploring mechanisms of sex differences in longevity: lifetime ovary exposure and exceptional longevity in dogs by Waters DJ, Kengeri SS, Clever B, Booth JA, Maras AH, Schlittler DL, Hayek MG
Published in the December 2009 issue of Aging Cell.

To be clear, we at Newcastle do not support careless breeding; in fact we advocate strongly for a careful and extensive evaluation of health, conformation, and temperament before any breeding is done. We do strongly oppose mandatory sterilization laws that generally require the removal of a dog's reproductive system by four to six months of age, for a variety of reasons including the fact that they have not worked to reduce shelter populations anywhere they've been tried, they disregard the health risks to the dogs, and at the root of it they are a government-mandated medical procedure. We know full well that it is entirely possible to own an intact dog without ever producing an unplanned litter, and that sterilization is in most cases a matter of owner convenience more than anything else. In some European countries, in fact, sterilization is only done if medically necessary and is considered animal cruelty in any other case. We are not opposed to sterilization, but we feel it is a decision that is best made on an individual basis by an owner in consultation with their veterinarian after careful review of all the facts.