You don’t need to be in the dog world for very long before you hear about desexing benefiting the health of dogs. These claims talk about reducing cancer (testicular, mammary, prostate, ovarian, uterine, cervix), reducing prostate disease (in boys), and preventing pyometra (in bitches).
What we don’t hear about is the undesirable side effects of desexing, and how desexing is linked to increased risks of some cancers, and an increased likelihood of joint disorders.
Torres de la Riva et al, in their research published just this month, decided to look into the health effects of desexing in golden retrievers; Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers.
They, indeed, hit back at these spruced ‘health benefits’ in the introduction of their piece, saying:
“In contrast to the rather strong evidence for neutering males and/or females as a risk factor for osteosarcoma, hemangiosarcoma, lymphosarcoma, mast cell tumours and prostate cancer, evidence for neutering as protection against a dog acquiring one or more cancers is weak.”
This research set out to investigate spay and neuter in Golden Retrievers from 1-8 years. They chose goldens because they are commonly used as assistance animals, and so they hoped the implications of this study may have consequences for related assistance organisations (of course, dog science only happens when it helps people!). It makes sense: it’s ‘wasteful’ to invest in a dog becomes invalid for the work they were trained in, especially if that invalidity could’ve been prevented by more-appropriate timing of desexing.
While other research has pooled many breeds and health affects together, this is the first study to look at desexing in just one particular breed. Prior-analysis determined several conditions to look at: hip dysplasia, cranial cruciate ligament tear, lymphosarcoma, hemangiosarcoma, mast cell tumours, osterosarcoma, and elbow dysplasia.
Dogs were included in the study if they were between 1-8 years of age. They were put into categories of either ‘early neuter’ (before 1 year of age), ‘late neuter’ (after 1 year of age), and ‘intact’. Data regarding their health was retrospective, gained from veterinary records. Any dogs where a health diagnosis was ‘grey’ (non-conclusive), they were excluded from the study.
Males who were desexed early had twice (10.3%) the incidence of hip dysplasia than intact males (5.1%). Males that were late-neutered had a hip dysplasia rate of approximately 3%.
In bitches, approximately 5% of early-spayed bitches got hip dysplasia. Intact and late-neutered bitches had hip dysplasia rates of approximately 3%. This difference was not statistically significant.
This is in keeping with research (quoted within this research) that indicated that desexing increases the likelihood of hip dysplasia by 17%.
Cranial Crucial Ligament Tear
No intact dogs, males or females, got cranial crucial ligament tears. Animals that were neutered early were more likely to get tears (5.1% of boys and 7.7% of bitches). No late-spayed bitches developed a tear, and only 1 dog developed a tear (1%).
This is consistent with research that showed a 3-fold increase in excessive tibial plateau angle in desexed dogs (of both sexes, across all breeds). This excessive tibial plateau angle is a risk factor for crucial ligament tears.
Approximately 3% of intact males got lymphosarcoma, compared to 9% of early-neutered males, and 0% of late-neutered males. In bitches, approximately 1.5% of intact bitches got lymphosarcoma, compared to 6% of early-spayed bitches, and 1% of late-spayed bitches. The research states, ”Although the rates of occurrence of this disease were lower in both male and female intact dogs, than in the early-neutered dogs, the difference was statistically significant only in males. Early-neutered males had nearly 3 times the occurence of [lymphosarcoma] as intact males and no cases of [lymphosarcoma] were observed in the late-neutered males”.
The results of this study are not dissimilar to others quoted, where intact females were at a significantly lower risk of developing lymphosarcoma than neutered females, or males (entire or desexed).
Intact males and early-neutered males had an incidence of hemangiosarcoma of around 3%, while only 1% of late neutered dogs got hemangiosarcoma. This difference was not statistically significant.
In bitches, the difference was more significant (statistically and otherwise!): 7.4% of late-neutered bitches were diagnosed with hemangiosarcoma, which was over 4 times the frequency seen in intact (1.6%) and early-spayed (1.8%) bitches. Late neutered bitches also got hemangiosarcoma early (3.2 years old), while intact and late-spayed bitches got the cancer later (at 6.4 years and 7.6 years respectively).
This is in keeping with existing research that shows that hemangiosarcoma occurs 4 times more in spayed females than those intact, and spayed females had more than 2 times the risk of developing splenic hemangiosarcoma than intact bitches.
Mast Cell Tumours (MCT)
This research found that approximately 3% of the intact males got MCT, approximately 2% of neutered early males got MCT, and about 4% of late neutered males got MCT. Clearly, these results were not statistically significant.
However, while no intact bitches got MCT, 2.3% of early-desexed bitches did, and 5.7% of late-neutered bitches developed tumours.
This is consistent with other research that showed cutaneous mast cell tumours had a 4 times greater frequency in neutered females than intact females.
The incidence of osterosarcoma was so small in this study that it was excluded from analysis. Other studies (quoted in this research) showed that osteosarcoma occurred 2-times as often in neutered relative to intact dogs, while another study showed that neutering prior to 1 year of age increased the occurrence of osteosarcoma 3-4 times.
Other health implications (elbow dyplasia and mammary cancer)
Body condition scores were used to control for extra weight in neutered dogs, but the scores were similar between groups (neutered and entire).
In regard to Mammary Cancer (MC), the study says, “No cases of MC were diagnosed in intact females in this study. This finding is partially explained by the relatively low frequency in which MC is diagnosed in Golden Retrievers. While this finding contrasts with the general concern expressed about the risk of MC in gonadally intact females, it is consistent with recent findings from a systematic meta-analysis finding a weak link, if any, between neutering and a reduce risk of MC.”
This study also quoted other research, that found that prostate cancer occurred four times as frequently in neutered males as intact males.
Results In Graphs
If you’re a visual person, you may appreciate the graphs to illustrate the results of this study.
HD: Hip dyplasia; CCL: Cranial crucial ligament tear; LSA: Lymphosarcoma; HSA: hemangiosarcoma; MCT: Mass cell tumours.
HD: Hip dyplasia; CCL: Cranial crucial ligament tear; LSA: Lymphosarcoma; HSA: hemangiosarcoma; MCT: Mass cell tumours.
Why would desexed dogs get joint problems?
It is likely that the joint problems (hip dyplasia and cranial crucial ligament tears) investigated in this study are more likely to occur due to neutering’s affects on growth plate closure. Other factors include breed related vulnerabilities, and sex related closure speeds (i.e. the growth plate closes more quickly in males than females). This may be why the occurrence of hip dyplasia in early-neutered males is double that of hip dyplasia in intact males.
Why would desexed dogs get cancer?
This is a harder question to answer. It’s believed that estrogen acts on “microsatellite instability” – or the likelihood of parts of DNA to change, which is linked to cancer. Estrogen effectively stops microsatellites for being ‘so changing’. When sex organs of bitches are removed, estrogen is also reduced, and so it can no longer act upon microsatellites and so cancer is more likely. However, it is also hypothesised that bitches need to have a heat cycle for estrogen to have this protective affect. This is why late neutering is perhaps associated with higher rates of hemangiosarcoma and mass cell tumours in entire and early-neutered bitches. There is a lot to learn in this area, and a lot more research needs to take place to understand the affects of hormones on cancer.
Conclusions from this Research
This research concludes that:
- Early neutering is associated with an increased occurrence of hip dyplasia, of cranial crucial ligament tears, and of lymphosarcoma.
- Late neutering was associated with the subsequent occurence of mass cell tumours and hemangiosarcoma in bitches.
- Affects of neutering on elbow dyplasia, osteosarcoma, and mass cell tumours were excluded from the study due to low sample number.
- There was a statisical difference in the health of early desexed and intact animals, and early desexed and late desexed animals, but not late desexed and intact animals. (That is, early-desexed animals had different health implications to late-desexed and intact dogs, but late-desexed and intact dogs had similar health.)
- The researchers call for this research to not be generalised to other breeds.
- For all five diseases analysed in this study, when an intact dog had a disease, it only occurred at one fourth or one half the rate of dogs that were early- or late-desexed.
- Recommended that males not be neutered before puberty to avoid problems of hip dyplasia, cranial crucial ligament tear, and lymphosarcoma. (But noted that even late neutering male be associated with age-related cognitive decline, as seen in other research.)
- For bitches, there is no clear recommendations. Early-neutering significantly increases the incidence of cranial crucial ligament tears from near 0 to almost 8%, while late neutering inreaces the risk of hemangiosarcoma to 4 times that of the 1.6% rate seen in intact females. Late neutering also was associated with mass cell tumours (5.7%), compared to no occurances in intact females. (As a personal comment, it seems from this research that leaving bitches in tact may be the best for their health. I am curious why the researchers did not make this suggestion.)
Criticisms of Research
This researched used veterinary records for this study, which means they were primarily using ‘ill’ dogs for their research. Some have argued that this research should’ve been more population based (though I’m not sure how easy it is to get population data of this sort).
Some have also theorised that perhaps the dogs that are entire were left entire because of superior health and conformation, meaning they were less likely to suffer from these conditions. That is, mostly ‘pet’ quality dogs were desexed, and more ‘high quality’ or ‘show quality’ dogs were left entire.
Further research needs to consider the other types of cancers and risks associated with leaving dogs entire. A similar study looking at rates of testicular, ovarian and cervix cancer is well needed. Research also needs to consider non-cancer problems, such as prostate issues and pyometra, which are also a risk for dogs that are kept entire.
The research indicates that this should not be generalised to other breeds, so it makes sense that this research should be replicated to other breeds to see if consistent themes emerge.
As noted, more attention needs to be given to how estrogen seems to be tied with cancer.
Torres de la Riva, G., Hart, B., Farver, T., Oberbauer, A., Messam, L., Willits, N., & Hart, L. (2013). Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers PLoS ONE, 8 (2) DOI: 10.1371/journal.pone.0055937
Further reading on this study:
New Study: Neutering affects dog health from Time 4 Dogs.
Golden retriever study suggests neutering affects dog health from UC Davis.
New study find early neuter doubles the risk of hip dysplasia in dogs from Dogs Naturally.
What have we been saying from Angry Vet.
Another research paper on health impact of spay/neuter from the KC Dog Blog.
Studying the study from Victoria Stilwell.