Historically, vets have been actively encouraging clients to neuter their pets as early as possible to try and prevent overpopulation. In 2017, Dogs Trust cared for 15,446 dogs across their 21 rehoming centres, and resources for these centres are often seriously overstretched. This article will discuss neutering in dogs, cats and rabbits.
● Behaviour. I am asked quite often in the consulting room, usually by the owners of young, energetic male dogs, if castration will 'calm him down'. There is no guarantee that castration will alter boisterous behaviour, as many behaviours in dogs can become learned, rather than hormone associated. The same is true of aggressive behaviour. I recommend that entire male dogs with aggression issues are assessed by a qualified behaviourist before neutering. Neutering is not necessarily the ‘cure’ for aggressive behaviour, and needs assessing on a case by case basis. Male dogs may display inappropriate sexual behaviour. There has been a reported 70% reduction in mounting or 'humping' behaviours after castration.
● Roaming. Entire male dogs (and cats) may roam for miles in search of a mate, increasing the risk of injury by road traffic accident. Roaming is reduced by 90% when males are castrated.
● Retained testicles. The testicles start descending from behind the kidneys, where they form when the puppy is in the uterus. They are usually descended into the scrotum by 8 weeks of age. If one (or both) testicles are not descended by 6 months of age, they are usually stuck or ‘retained’ somewhere, either within the abdomen or in the groin area. If a testicle is retained, there is a ten times greater risk of it becoming cancerous. A male dog or cat with retained testicles is not a candidate for breeding and should be neutered.
● Testicular cancer. Testicular tumours account for 5% of all canine tumours. Two types of tumour (sertoli cell tumours and seminomas) have a 10% chance of spreading throughout the body, so they can be nasty. There may be more than one type of tumour in the same testicle. Testicular tumours are most often seen in entire male dogs of 10 years of age or older. Castration prevents testicular tumours.
● Prostate disease. There is a misconception that entire male dogs are at higher risk of prostate cancer. 5% of male dogs with prostate disease have cancer and castration is not thought to affect this risk. There is a 0.5% risk of prostate cancer in castrated males. However, entire males are at greater risk of conditions which increase the risk of prostate cancer, such as an enlarged prostate (benign prostatic hyperplasia or BPH) and inflammation or infection of the prostate. Prostate infections can be very serious. 95-100% of entire males will have some degree of benign prostatic hyperplasia by 10 years old. Castration cures BPH and reduces the risk of prostate disease.
● Perianal adenoma/adenocarcinoma. Tumours of the anal area are common in middle aged to older, entire male dogs. They may be benign or malignant (aggressive). Aggressive forms may spread to the lymph nodes and into the pelvic canal and cause problems urinating or defaecating. We don't fully understand how, but the tumours grow under the influence of male hormones. They are uncommon in female dogs. Benign perianal adenomas usually disappear after castration.
● Mammary tumour risk. Mammary tumours account for 25% of all canine tumours. 50-70% of all tumours in bitches are mammary tumours, making them the second most common tumour after skin cancer. 40% of mammary tumours are malignant. Malignant tumours are more common in larger breed dogs (58%) compared to smaller dogs (25%). Mammary tumours grow in response to female hormones. Tumour growth can be rapid and spread to the lungs is common.
If a bitch is spayed before puberty, at 6 months of age, then the mammary tumour risk is at its lowest rate, 0.5%. After the second season, spaying will not reduce the risk of mammary tumours.
● Pyometra - in entire bitches, the uterus lining can become overactive, a syndrome called CEH (cystic endometrial hyperplasia). Secondary bacterial infection may lead to a life threatening emergency, a pyometra, where the uterus fills with pus and can rupture into the abdomen. Pyometra is estimated to occur in 25-66% of unspayed bitches of 9-10 years old. Spaying prevents pyometra occurring.
● Population control. Cats are prolific breeders, and can become sexually mature from as young as 4 months of age. Cats Protection estimates that one female cat can produce 20,000 descendants within a few years. A female cat may produce 3-4 litters in a year, and she can become pregnant again within 2 weeks of giving birth. Animals have no social boundaries when it comes to sexual behaviour, and this can result in inappropriate mating between direct relatives.
● Roaming and fighting. Male cats can sense a female in heat from several miles away, leading to roaming behaviours in order to find a mate. Tom cats may fight other cats and display territorial aggression or spraying. Fighting is a risk factor for spreading FIV (Feline Immunodeficiency Virus) which is spread between cats by bites from infected cats.
● Tumour risk. Male cats are rarely affected by prostate disease or testicular
cancer. The mammary cancer risk in female cats is half that of dogs. However there is an 86% reduction in mammary cancer risk if the female cat is spayed before 1 year of age.
Rabbits reach sexual maturity from 4-6 months of age. Both sexes can be affected by territorial aggression. Does (females) may experience false pregnancies, which can worsen aggressive behaviour.
● Males - neutering males reduces territorial aggression. Entire male rabbits may spray urine and fight with one another, or be aggressive towards their owners.
● Females can come into season 10 times a year and a female may breed constantly through her life. Uterine cancer is very common in unspayed females, affecting 50-80% of entire females over the age of 3 years. The cancer can be aggressive and spread throughout the body. Neutering will prevent uterine cancer if it is carried out before 2 years of age. Rabbits may be safely neutered from 4 months of age.
When is the best time to neuter?
● Male dogs reach sexual maturity by 6-9 months of age.
Neutering can safely be carried out from 6 months. For larger breeds or active dogs it may be appropriate to neuter at 12-18 months of age when they are more physically mature.
● Bitches become sexually mature (first season) from 6-12 months of age, and come into season approximately every 6 months.
It is safe to spay before the first season at 6 months, or 3 months after the first season.
● Cats become sexually mature from as young as 4 months of age.
We can safely neuter cats from 5-6 months.
Are there any risks?
With any surgery, there may be risks of blood loss, infection after the operation, and the general anaesthetic itself. We can advise further on the way these risks are managed.
I heard that there are health benefits to letting my female cat or dog have a litter, is this true?
There are no proven health benefits to this. Indeed, dystocia (problems giving birth) can be life threatening for the mother and the litter, and can require emergency surgery. There are also many thousands of animals in rescue centres in need of homes.
What factors are important to consider when deciding whether or not to neuter?
● A recent study on some large breed dogs found that early neutering (< 6 months of age) increased the risk of joint disease such as hip and elbow dysplasia, and cruciate ligament rupture. These conditions were also influenced by other factors including diet, genetics, and exercise.
● If an animal has a medical condition making neutering unsafe.
● Some breeds may be more susceptible to certain cancers after neutering. There is conflicting evidence on this subject.
● Obesity – if the animal is already obese when undergoing surgery, the anaesthetic risks are higher, the surgery is more difficult (especially in females) and the risk of further weight gain post surgery is higher. We can advise on weight management prior to surgery.
● Weight gain may occur after neutering. It is important to continually reassess an animal’s nutritional requirements according to their activity level.
● Breeding stock, or showing/working dogs.
● A recent study suggests that 5% of bitches spayed at over 12 weeks of age will develop urinary incontinence. The incidence is higher in large breeds (9%) compared to small breeds (1%).
● Neutered animals’ hair coats may develop a different texture (does not usually affect the animal)
Are there any alternatives to neutering?
Hormone injections (bitches) and hormone implants (male dogs) are available. In bitches this may increase the risk of pyometra.
Neutering - Is it worth it?
Animals unsuitable for breeding (retained testicles, deformities, heart murmurs, umbilical hernias) should be neutered to avoid passing these traits on.
Studies have demonstrated breed specific considerations for neutering. These cannot be used to decide on risks for all dogs. For large breed dogs, it may be appropriate to wait until they are over 1 year old before neutering.
Neutering male dogs significantly reduces the risk of testicular cancers and prostate disease. Neutering female dogs significantly reduces the risk of life threatening illnesses such as mammary cancer and pyometra.
These health benefits ought to outweigh the risks of conditions where neutering presents a minor risk. Before neutering it is best practice to assess each individual in terms of breed, body size, and breed specific disease risks.
Do you want to know more?
Howe (2015) Current perspectives on the optimal age to spay/castrate dogs and cats, Vet Med (Auckl) 2015; 6: 171-180
Vetstream, an online resource for vets
Hart et al (2014) Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers, PLoS One, 2014, 9(7) e102241