Neutering and spaying
Neutering and spaying of male and female dogs in their first year of life has become a routine procedure in the US and much of Europe. For decades, veterinarians and animal associations have promoted neutering as a means to preventing unwanted litters and health complications.
Animal owners carry out this medical intervention for its practical purpose but also because it has health benefits. Not only does neutering reduce many of the unwanted behavioural problems associated with the mating instinct such as aggressiveness, fleeing, digging, and marking, but it also protects against some serious health issues.
Spaying has health benefits
Spaying an animal prevents uterine infections, prostatic hyperplasia, or breast, ovarian or testicular cancer. Almost 1 in 3 dogs will develop a testicular tumour in their lifetime, and only 50% will survive it. Equally, bitches spayed before their first, second or third heat-cycle have respectively 0.5%, 8% and 26% risk of developing mammary cancer.
Taking away the reproductive and hormone producing organs of animals seems to decrease their chances of developing quite deadly tumours.
Until recently, veterinarians often advised strongly in favour of early neutering. The benefits of sterilisation seemed unequivocal. However, research into the topic of the health impacts of neutering is showing a much more complex situation than once thought.
A complex association
Overall, the data is complex and inconsistent, but a growing body of research seem to incriminate neutering as a risk in the development of some types of cancer including lymphoma, mast cell tumour, hemangiosarcoma and osteosarcoma. There is also evidence of a relationship between neutering and debilitating joint disorders such as hip dysplasia, cranial cruciate ligament tear or rupture, and elbow dysplasia. The last example here is that affecting brain function.
This research is complicating pet owners' decisions on neutering. However, there isn’t a clear-cut relationship. Many factors need to be taken into consideration when looking at the relationship between interventions such as sterilisation and cancer. These can depend on the age when spayed, the breed, body size and sex.
All studies seem to be sure of one thing, the trends are not universal. Some cancers almost certainly occur less often following neutering, and others almost certainly occur more often.
For example, tumour risk in the mammary glands in entire dogs is higher than in neutered animals, particularly for small breeds who are at a higher risk of developing tumours of the mammary gland and the endocrine glands than large breeds. So hormones seem to clearly impact tumour development but not always in a bad way.
Neutering can also be linked to a reduced risk of adenocarcinomas, the most common type of cancer found, especially in females. Since over 60% of the adenomas/adenocarcinomas are found in the sexual organs, this primarily relates to breast cancer, which occurs much more often in intact females than in neutered females or males.
This link between cancer and neutering is likely to have a genetic component, manifested by the tendency of certain breeds to develop certain types of cancer. Different dog breeds also have different overall cancer risk.
When scientists started to factor in the time when neutering occurred in a dog’s life, the association with cancer or joint disorders got even more complex. Globally early neutering seems to have a more negative impact than a later operation however, this largely depended of the size of the breeds and their genetic background.
Factoring in methodologies
Interestingly, the effect of neutering status on tumour development seem to be partly dependent on the examination method, specifically on whether the animal is dead or alive at the time of diagnosis. Tumour incidence in post-mortem samples seem to be higher in neutered than in entire dogs, suggesting bias through investigation of mammary glands and testes in ex-vivo materials. This might explain why an important amount of studies seem to correlate neutering to cancer development. It is important to factor in collection method when examining these studies.
When scrutinised, the studies that seem to incriminate neutering as a cancer causing agent also seem to mostly focus on very specific cases.
The best way to identify real trends is to compare data from different studies, often involving different populations (ages, breeds, geographic locations, etc.) and study methods (clinical patients, cancer registry studies, pathology lab studies, insurance company data, etc).
Breed associated recommendations
In an attempt to address the absence of breed-specific information on joint disorders and cancers associated with neutering, a study from the School of Veterinary Medicine in California scrutinised 35 different dog breeds. They analysed data and analyses in their extensive veterinary hospital database where the same diagnostic criteria could be applied to all breeds. The objective was to uncover specific risks of developing joint disorders, cancer or urinary incontinence according to age of sterilisation.
In most cases, the age of sterilization did not necessarily seem to increase the risk of developing joint disorders and/or cancer. However, each dog breed is different. Smaller breeds seem less at risk. Only the Boston Terrier and the Shih Tzu show a significant increase in cancers after neutering.
This study has put together recommendations, specific to each of the 35 dog breeds studied.
|
|
Males |
Females |
|
Australian Cattle Dog |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Increased risk of joint disorders after sterilisation < 6 months. Recommended to sterilise after 6 months. |
|
Australian Shepherd |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, some cancer risk may be associated with neutering after 6 moths, or no neutering at all, especially breast cancer. |
|
Beagle
|
Possible increase in joint disorders with sterilisation between 6 and 11 months - recommend sterilisation after 1 year |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Bernese mountain dog
|
Risk of joint disorders - recommended to delay sterilisation well beyond 2 years. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Border collie
|
Increased risk of developing cancer after sterilisation – recommended to delay sterilisation well beyond 1 year. |
Increased risk of developing cancer after sterilisation – recommended to delay sterilisation well beyond 1 year. |
|
Boston Terrier
|
Significant increase in cancers in males castrated before 11 months – recommended to delay sterilisation after 1 year. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Boxer
|
Increased risk of developing cancer after sterilisation – recommended to delay sterilisation well beyond 2 years. |
Increased risk of developing cancer after sterilisation – recommended to delay sterilisation well beyond 2 years. |
|
Bulldog
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Cavalier King Charles
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Chihuahua
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Cocker Spaniel
|
recommended sterilisation after 6 months. |
Increased risk of cancer after sterilisation < 1 year. Recommended to sterilise after 2 years. |
|
Colley
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Increased risks of cancer after sterilisation |
|
Welsh Corgi Pembroke and Cardigan |
Increase in intervertebral disc pathologies after sterilisation |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Dachshund
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Doberman Pinscher (limited data) |
Increased risk of cancer in males castrated after 1 year- recommended not to neuter or do so early before 1 year. |
Increased risk of urinary incontinence and joint disorders – recommended to delay sterilisation after 2 years |
|
English Springer Spaniel |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Increased risk of urinary incontinence after sterilisation < 1 year. Recommended to sterilise after 1 year. |
|
German Shepherd
|
Risk of joint disorders - recommended delay sterilisation beyond 2 years. |
Risk of joint disorders - recommended delay sterilisation beyond 2 years. |
|
Golden retriever
|
Risk of joint disorders and cancer - recommended delay sterilisation beyond 1 year. |
Increased risk of developing cancer after sterilisation – recommended not to sterilise or to do so after 1 year while remaining vigilant. |
|
Great Dane
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, given the large body size and physiology of late musculoskeletal development, sterilisation well beyond 1 year should be considered. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, given the large body size and physiology of late musculoskeletal development, sterilisation well beyond 1 year should be considered. |
|
Irish Wolfhound |
Increased risk of cancer in males castrated between 1 & 2 years- recommended to delay sterilisation beyond 2 years |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, given the large body size and physiology of late musculoskeletal development, sterilisation well beyond 1 year should be considered. |
|
Jack Russell Terrier
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Labrador Retriever
|
Risk of joint disorders in males castrated |
Risk of joint disorders in females castrated |
|
Maltese Bichon
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Miniature Schnauzer
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Dwarf Spitz
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Toy poodle
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Miniature poodle
|
Risk of joint disorders - recommended delay sterilisation after 1 year. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Poodle
|
Increased risks of cancer after sterilization at 1 year - recommended to delay sterilisation beyond 2 years. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Pug
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
Rottweiler
|
Risk of joint disorders in males castrated |
Risk of joint disorders in females neutered |
|
Saint-Bernard
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, given the large body size, sterilisation well beyond 1 year should be considered. |
Risk of joint disorders in females neutered |
|
Shetland Sheepdog
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Risk of urinary incontinence - recommended delay sterilization well beyond 2 years. |
|
Shih Tzu
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Increased risks of cancer after sterilisation between 6 months & 1 year, reaching up to 18% if carried out at 1 year - recommended early sterilisation at 4 or 5 months or to delay after 2 years. |
|
Westie
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, delaying sterilization after & year could avoid the risk of urinary incontinence |
|
Yorkshire Terrier |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
Source: https://www.frontiersin.org/articles/10.3389/fvets.2020.00388/full
Researchers also tried to do the same for mixed breeds, although this time based more on size rather than breed type. Their research showed that mixed breed dogs weighing 20 kg and above had significant increases in joint disorders with early neutering. Those below 20kg didn’t seem to be affected with this incidence. Regarding cancer occurrence, larger dogs were more affected generally. Up to 15% of intact dogs seemed to be affected, especially the heavier one, but there was no evidence that neutering affected those numbers. However, it is important to bear in mind that these numbers were calculated based on middle aged dogs and could evolve with age.
Here is a summary of the recommendations.
|
Mixed dog breeds |
Males |
females |
|
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
|
10–19 kg |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age. |
|
20–29 kg |
Risk of joint disorders in males castrated early - recommended delay sterilisation after 1 year. |
Risk of joint disorders in females neutered early - recommended delay sterilisation after 1 year. |
|
30–39 kg |
Risk of joint disorders in males castrated early - recommended delay sterilisation after 1 year. |
Risk of joint disorders in females neutered early - recommended delay sterilisation after 1 year. This also avoids the vulnerability to UI in early-spayed females. |
|
over 40 kg |
Risk of joint disorders in males castrated through 1 year - recommended delay sterilisation after 2 years. |
No increased risk of joint disorders or cancer - sterilisation can be done regardless of age, however, given the large body size, sterilisation well beyond 1 year should be considered. |
Source: https://www.frontiersin.org/articles/10.3389/fvets.2020.00472/full?from=article_link
Last edited: 1 March 2023 14:58