When to Spay or Neuter

For 25 years those of us in the veterinary community have recommended early neutering and spaying for dogs. In the past, we always recommended spaying or neutering your dog anytime at or after the last set of shots – usually around 4 months of age.

However, new research and information on the effects of sex and growth hormones on the structure and microscopic anatomy of bones, cartilage, tendons and ligaments on the growing puppy have forced us to change our recommendations regarding when to spay or neuter your dog. In addition to that, there is convincing evidence of the tie between early sterilization and the increased prevalence of certain tumors and cancers in older animals.


Recent Neutering Controversies

Over the years there have been a number of studies which indicate an increase in some forms of cancer in gonadectomized (neutered or spayed) male and female dogs.  A recent breed specific study also reviewed the correlation between an increased risk of certain joint disorders, and a second breed specific study indicated a possible correlation to behavior issues.

Because neutering interrupts production of certain hormones that may have key roles in closure of bone growth plates, the study of joint disorders was of particular interest.  Because it is possible that hormones may affect other body processes, the results of these studies have raised the question of the possible beneficial effects that sex hormones – which are removed by neutering – may have on dogs.

In February, 2013, a study of Golden Retrievers, recording the incidence of hip dysplasia (HD), cranial cruciate ligament tears (CCL), lymphosarcoma (LSA), hemangiosarcoma (HAS), and mast cell tumors (MCT) was published.

This retrospective study was based on 759 client-owned intact and neutered male and female Golden Retrievers aged 1 – 8 years of age admitted between January 1, 2000 and December 31, 2009 to the Veterinary Medical Teaching Hospital at U.C. Davis.

The study indicates that early neutering (before 12 months of age) was associated with an increase in the occurrence of hip dysplasia, cranial cruciate ligament tear and lymphosarcoma in male dogs.

The dogs were categorized as intact, neutered early (before 12 months of age) or neutered late (after 12 months of age).  The chart below (taken from the study) indicates the number of male dogs for each category that were positive for any of the 5 diseases or disorders compared with the total number of dogs in each category:

Effects of Early Neutering

Male dogs neutered after 12 months had no incidence of lymphosarcoma.

AVMA Study on 2500 Vizslas

A retrospective cohort study on 2,505 Vizslas born between 1992 and 2008 was published in the February, 2014 journal of the American Veterinary medical Association.

This study concluded that the odds of MCT and LSA were higher for neutered dogs verses intact dogs, but male dogs neutered before 6 months of age did not have an increased risk of developing HSA.  For cancers other than those three, the incidence of cancers included in the study were higher for neutered than intact dogs.

While many studies are giving dog owners cause for concern when considering whether or not to neuter their pets, a recent University of Georgia study has come out with interesting results regarding the lifespan of neutered and intact dogs.

The medical records of sterilized and intact dogs whose hospital visits to North American veterinary teaching hospitals resulted in death between the years 1984 – 2004 was obtained from the Veterinary Medical Data Base. This cohort study found that the mean age of death for intact dogs was 7.9 years versus 9.4 years for sterilized dogs.  And while this study also showed that sterilization increased the risk of death due to some forms of cancer, it did not increase risk for all specific kinds of cancer.

The authors make an interesting point, “The increased risk of death due to cancer observed in sterilized dogs could be due to the fact that in both sexes, dogs sterilized before the onset of puberty grow taller than their intact counterparts as a result of reduced estrogen signaling. Recent studies in humans suggest that growth is a risk factor for a number of different cancers.”

The study also showed that dogs which had been sterilized had a decreased risk of death due to infection, noting, “The relationship between sterilization and infectious disease could arise due to increased levels of progesterone and testosterone in intact dogs, both of which can be immunosuppressive.”

And indeed, there certainly are some male dogs for whom castration becomes a medical imperative (perineal hernias, benign prostatic enlargement, etc.).


The relationship between neutering and disease-risk is a complex issue. While some studies indicate a relationship between gonadectomy and an increase in certain cancers, it cannot be determined whether or not the decrease of certain hormones has a protective role without further studies.  Additionally, if hormones do play a role in limiting the occurrence of certain cancers, there are no long term studies that indicate whether the amount of testosterone which is retained in dogs which receive Zeuterin (which can vary between dogs) will decrease their risk for those cancers.

It is also important to take into account the fact that different dog breeds have different vulnerabilities to various diseases.  While there have now been a few breed specific studies, the effects of early and late neutering also may vary from breed to breed, and warrants further study.

The increased incidence of joint diseases among early-neutered dogs seen in some studies may be due to the effect of neutering on young dogs’ growth plates, and therefore the timing of neutering, based on dog breed, may be able to offset these issues.  Further studies on joint diseases among neutered vs. intact dogs are needed to draw more accurate conclusions.

It might also be helpful for studies regarding joint diseases to evaluate whether or not there is a correlation between activity levels in neutered and intact dogs; i.e. do more neutered dogs participate in dog sports such as agility and flyball than intact dogs, increasing the occurrence of joint disease?

Until more information becomes available we will continue to recommend neutering or spaying at 12 months of age. Look for our future posts on the effects of neutering on behavior training, and whether or not chemical neutering (zeutering) can achieve the same results as surgical castration.