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The Pros & Cons of Neutering (Summarised)

I currently have two in-depth and detailed blogs focussing on spaying and castrating of dogs. I am however aware that these are long, technical and filled with research. Whilst I strongly encourage all owners to read through these blogs, I have compiled a summary of the findings. I would like to mention that in the full blog, I have explained why some of the findings may not be as cut and dry as they may appear based on numbers. There is a lot to consider with research which includes methodology and other external factors which may have affected the results. There is also a huge concern of causality (did the procedure actually cause the problem/prevent the problem or was this in fact due to something else that is more common in neutered/intact animals or simply chance). So I urge those who just read this blog to do so with care and consider reading my full blog post for a more complete picture.

Female dogs - I will start with female dogs and the medical/behavioral pros and cons to desexing.


  • 16.8% of females will get Mammary Neoplasia. 72-74% of these will be intact.

  • The risk of mass cell tumours, hemangiosarcoma and lymphoma was higher in spayed bitches (3-4 times higher in Golden Retrievers).

  • Several pieces of research have found that early spaying (particularly before the age of 7 months), leads to a marked increase in chance of the dog developing hip dysplasia.

  • Urinary Incontinence occurred in 5 - 20% of spayed bitches compared to only approximately 1% of intact females.

  • Weight gain has been associated with the spaying of a female dog and in turn this has increased the chance of spayed females developing diabetes.

  • Two studies showed spayed females had increased incidences of patella luxation.

  • Those who have been spayed are at no risk of pyometra developing. The risk of pyometra increases as the unspayed bitch ages. By the age of 10, almost 25% of unspayed females will have been affected by this. This is a life threatening condition and one all owners of intact bitches should be aware of and research.

  • One study looked at over 22,000 dogs and found that spayed females were more frequently diagnosed with atopic dermatitis, autoimmune disorders, hypothyroidism, inflammatory bowel disease and lupus.

  • One study looking at over 100,000 dogs found that spayed dogs were more likely to suffer with chronic kidney disease.

  • Spaying eliminates the risk of pregnancy which has its own set of medical risks for your bitch. This also has financial concequences and time which many poeple will not be able to accomodate.

  • The increased risk in many of these was increased further with a younger age of spaying.


  • Dogs who were neutered under 5.5 months had fewer incidences of separation anxiety but a greater chance of aggression towards family and strangers.

  • In a study of over 13,000 dogs, those who were neutered before the age of 6 months had significantly more incidences of aggression towards family members.

  • For dogs who were not yet reactive, results suggested that spaying of a bitch may induce a reactivity problem. For dogs who were already reactive, this appeared to increase reactivity.

  • Amongst this research into aggression, those that controlled for age of spay found that the effects were significantly more detrimental if the dog was spayed earlier. Those neutered before 6 months the most affected, followed by those neutered between 7 – 12 months in fear and anxiety scores.

  • Spaying eliminates the chance of phantom/pseudo pregnancy which can offer temporary temperament and behaviour changes in your dog.

  • Spaying stops dog's seasons and can avoid inter-dog aggression between household dogs (particularly males).

  • Spaying means you do not need to keep your dog on a lead/away from other males for 6 weeks of the year.

  • From the current studies in the field, chewing & howling were actually seen more in dogs who had been left longer before being spayed, compared to those who had been spayed early.

  • Dogs who were neutered young were more likley to show high levels of excitement and by some were described as appearing to remain in a more juvenile state.

  • Spayed dogs performed worse in spatial learning, memory and other leaning tasks with 71% of intact females being able to perform these compared to 56% of spayed.

  • Spayed dogs were found to be “more obedient” than intact dogs. “Obedience” being defined by how focussed the dog was around distractions.

Considerations - Ovary Sparing Spays are an option which eliminates the risk of pyometra and pregnancy without the hormone related risks noted above.

Male dogs - I will now move onto male dogs and the medical/behavioral pros and cons to desexing.


  • Those who were castrated before their growth plates were fully closed led to extended growth plates and a greater risk of joint related problems in the future.

  • There was a higher number of cases of prostate tumours in castrated males.

  • When 1170 German Shepherds were studied over a 14.5-year period, 21% of dogs neutered before one year old were diagnosed with some form of joint disorder.

  • Cruciate ligament tear was one of the most common problem seen amongst neutered males.

  • Research has suggested there is a two-fold increase in osteosarcoma compared to intact dogs.

  • On a large study of over 40,000 dogs, neutered males were found more likley to die from cancers compared to intact dogs.

  • Neutering has also been found to increase the risk of canine obesity.

  • A study on Golden Retrievers found that 27% of dogs who were neutered before 6 months were diagnosed with joint disorders.

  • 15% of dogs who were neutered before 6 months were diagnosed with cancer. 11-15% of those neutered between 6 and 11 months were diagnosed and 11% of dogs who were left intact were diagnosed.

  • The risk of joint disorder if neutered before 6 months was twice as high as those who were intact or neutered over the age of 6 months.

  • Rottweilers neutered before the age of 1 were found to be 4 times more likley to be diagnosed with osteosarcoma.

  • Neutering was associated with an increased risk in the aggressiveness of prostatic cancer, hemangiosarcoma, lymphosarcoma and mast cell tumours.

  • When looking at 8 different cancers, neutered dogs were affected more frequently in 7 out of 8 cancers.

  • Neutered dogs were found to have a greater prevalence of immune disorders.

  • Infection of the brucella canis is transmitted through the mating of a male and a female dog. With an increased risk of this occurring in intact males.

  • In intact males, the second most common site of cancer is the testicles. Cryptorchid testicles are more likley to develop tumours in dogs under the age of 10 years. However, many testicular problems are slow to metastasize leading to only around 15% spreading to other areas.

  • The medical records of over 90,000 dogs were analysed and it was found neutered males were at less of a risk from congenital conditions such as aortic stenosis, early onset cataracts, mitral valve disease, patent ductus arteriosus, portosystemic shunt, ventricular septal defect, dilated cardiomyopathy, gastric dilation volvulus.

  • Neutering significantly increased their overall lifespan in one study conducted.

  • It is important to mention that some research has found no significant difference between dogs who are neutered and unneutered. This was noted in particular for lymphoma, hemangiosarcoma, osteosarcoma and mast cell tumours.


  • Neutering can reduce tension between intact males if you have an intact bitch in the household also.

  • Neutered males are more likely to react negatively to intact males than other intact males.

  • Neutered dogs scored higher for "trainability"

  • Intact males can attract unwanted attention from neutered males.

  • Castration may reduce aggression (1/3rd cases) however most research. suggests quite the opposite (that castration will likely increase aggression)

  • Neutered dogs were more likely to be labelled as "emotionally unstable"

  • Intact males were more confident than neutered males.

  • No significant change in marking and stress/excitement mounting behaviours.

  • Neutering reduces the risk of roaming and sexual mounting.

  • Neutering eliminates the risk of reproduction and the risks associated with this (STD's, injury during a tie, behavioural changes to being bred - increased interest in female dogs, increased intolerance around other male dogs).

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