The pros and cons of spay and neuter: Pete the Vet talks SpayAware on Newstalk’s Pat Kenny Show

Listen to the podcast by following the link at the foot of this page.

Spayaware was launched in 2002 as part of a nationwide grass roots effort by animal welfare groups, vets and individuals, to highlight the importance of spaying and neutering as a way of addressing Ireland’s pet overpopulation crisis. SpayAware also shares the pros and cons of spaying or neutering cats and dogs, and promotes the procedures as an important part of responsible pet ownership.

Now supported by ISPCA and Veterinary Ireland, Spayaware has become a year-long campaign. The first week of June every year – during what used to be called “SpayWeek” – is still the time when there is a particular focus on getting the message about spay/neuter into the public arena and consciousness​​.

There are two main reasons for spaying and neutering

Population control.

Ireland has a serious problem with unwanted puppies and kittens, and it’s estimated that around half of all pups are from unplanned pregnancies. If all pet dogs and cats were routinely spayed and neutered, the overpopulation problem would rapidly be solved.

Health benefits

Spay/neuter removes the reproductive hormones from the body, and this can have profound effects on the overall health of the animal. Most of the effects are positive, but there may be negative aspects for some animals, so a risk-benefit analysis should be carried out for each animal in conjunction with your local vet, who knows your pet.


As well as removing the inconvenience of regular seasons and the risk of unwanted pregnancy, spaying markedly reduces the risk of mammary cancer (the most common tumour in female dogs) and prevents pyometra (a serious condition involving an infected womb which is seen in 23% of  females that are not spayed).


Again, spaying removes the risk of unwanted pregnancies and the behavioural changes linked to being in season. It also dramatically reduces the risk of mammary cancer, which is the third most common tumour seen in cats.


Castration reduces the incidence of many conditions that affect the prostate gland (e.g. benign prostatic hyperplasia, prostatitis/prostatic abscesses, prostatic cysts and para-prostatic cysts). Around 95% of male dogs are affected by one or more of these conditions if they are not castrated.
Castration also reduces the risk of conditions affecting the perineum, around the anus, including perianal adenoma and perianal fistulas.
Castration reduces some types of aggression  in male dogs, lessens marking with urine, and reduces roaming and straying, as  well as lessening male driven behaviours like mounting people’s legs or furniture.


Neutering reduces fighting between cats by over 80%, preventing physical injuries as well as reducing the chance of picking up viruses such as FIV.  Male urine marking behaviour also reduces after a cat is castrated.

Are there adverse effects from spaying or neutering?

  • It has been reported that castration is correlated with an increased risk of bladder and prostate cancer, but these are very rare cancers compared to the conditions that are prevented by castration.
  • Spayed and neutered animals are more likely to put on weight because of the effect on the metabolism, but this can be addressed by adjusting diet and exercise before the animal gains weight. There are many lean neutered and spayed pets, just as there are many obese entire pets: although there is an effect from spay/neuter, this is more about how owners feed and exercise the animals in their care.
  • In large and giant breeds of dog, spaying and neutering before maturity may increase the risk of bone tumours (osteosarcoma) so it’s now recommended that these types of animals should not be neutered or spayed until they are skeletally mature (around 18 months of age). Small and medium sized breeds should  be neutered or spayed when younger (from 6 -7 months of age).  Different vets take differing views on the optimal timing of the operation, so it’s best to talk to your own vet about this.
  • Urinary incontinence is another potential negative impact:  between 4 and 20%) of spayed bitches develop this, compared with just  0.3% of unspayed bitches. The jury is still out about whether or not spaying before the first season marginally increases or decreases the risk of urinary incontinence, but in any case, the condition can usually be treated effectively with daily drops.
  • Recent studies have suggested possible links between spaying/ neutering and cardiac haemangiosarcoma, hypothyroidism, “doggy alzheimers”, urinary tract and splenic tumours, orthopaedic problems (such as ruptured cruciate ligaments), adverse vaccine reactions, recurring urinary tract infections,  and vaginitis if spayed before puberty.

These adverse impacts, even though they may be rare and relatively minor, demonstrate that there are pros and cons to any surgery: it’s a case of considering both sides before reaching a decision.

Summary of neutering and spaying pets

For most dogs and cats, neutering (of males) and spaying (of females) should be carried out in the first two years of life. It’s best to make the decision on an individual basis after discussing it with your own vet.

Questions from listeners

  • My bitch is spayed, but her brother is not neutered. We spayed her because having to take care of her while she was in heat was quite troublesome. Lately he’s been getting a bit rowdy with her, and humping her! He doesn’t know what he’s doing because he’s never done it right (if you know what I mean). Should we neuter him?
  • We recently took on 3 ex-battery hens. Two of them are laying, we don’t know why the third isn’t. They are a little aggressive towards us so have only handled them once since getting them about a month ago. I know they need protection against lice and mites – is there anything else we can do without handling them? Do they need to be vaccinated? And what is the best thing we can do to keep them happy little hens? Maria, Wicklow
  • Can you ask Pete about my Maltese dog Jack, who lately is knocking over his food?? I give him Canagan which is excellent food from pet store, @ 22 euro per 2Kg, I change the food each time i buy. i give him only the best leftovers into his bowl like pure chicken etc… Why is he knocking over his food? I come home the food is all over the floor. He is never left for more than 2 hours? Kind Regards, Sonia

To find out Pete’s answers to these questions, listen to the podcast below.

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1 Comment

  • Tiffany Locke says:

    Thanks for the information on how spaying reduces the risk of mammary cancer as well as gets rid of behavioural changes related to them being in season. This would probably be important to keep your animal healthy. When choosing a veterinarian to take care of the spaying, you’d probably want to make sure they have the experience and equipment to do it safely and correctly so your pet will be healthy and comfortable during the procedure in order to reduce any risk of disease or infection.

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