The health risks of not sterilising your pets

9th May, 2017

Written By Dr Shelagh Hahn

Animal lovers know that if you truly love your pets – and care about animals everywhere – you will have them sterilised. Aside from the massive animal overpopulation crisis, known to lead to neglect and abuse, there are many diseases, some life threatening, which you can avoid or completely prevent simply by having them spayed or neutered. Your pets really are worth it.

Veterinarian Dr Shelagh Hahn, B.V. Sc., of Blue Bush Veterinary Clinic in Randburg, explains.

Nature’s way?

Some argue that animal sterilisation is unnatural, but the fact is it’s not exactly natural for predatory carnivores to live in houses being fed by two-legged primates either! Dogs and cats are the responsibility of those who have domesticated them: human beings; this includes their health and population control. Those who argue that ‘sterilisation is unnatural’ are, effectively, also saying that it is natural (and thus acceptable) for pets to die in agony from entirely preventable cancers, infections or injuries.

Dogs, cats and other pets do not need a ‘sex life’ (another common argument, often from men) – they have no sex glands or hormones so they cannot miss ‘sexual’ behaviour. Only humans, dolphins and bonobo chimpanzees have a ‘recreational’ sex life, apart from instinctive mating when fertile.

Pets also don’t need to have a litter or go on heat at least once before being sterilised – this is a dangerous myth. Female animals will not miss being mothers. Having a young female dog or cat get pregnant with her first or second heat is the equivalent of letting your pubescent daughter have a baby. In fact, it has been proven to be infinitely better that sterilisation be done before this happens. Your children also do not need to see an animal give birth to understand the ‘miracle of life’ – especially considering that these ‘miracles’ usually end up being sent to shelters or terrible homes, or euthenised. That is not natural either.

Bottom line: given the circumstances in which we and our pets live today, the only thing ‘natural’ about not sterilising is that they (and/or their offspring or offspring’s offspring) will ultimately suffer in some way as a result of not having been sterilised.

Infectious diseases such as Transverse Venereal Tumours (TVTs), Feline Immunodeficiency Virus (‘cat AIDS’), chlamydia, canine and feline herpes virus, and canine brucellosis affect both male and female pets. Although they can sometimes be transmitted to sterilised animals, the chances of exposure and transmission are vastly increased by courtship fighting, mating behaviour, pregnancy and birth. By sterilising timeously (before six months of age), you can greatly reduce the chances of your pet contracting them.

Treatment with chemotherapy is usually successful in the early stages, but, in impoverished communities and strays, it is often seen too late when the cancer has widely invaded the dog’s system – and has been transmitted to numerous others. People often think it doesn’t affect them because they don’t live in a township, but your unsterilised dog could easily get out and encounter an infected stray.



The most common illness of unspayed females, pyometra, is a painful, potentially fatal bacterial infection in the uterus. In open pyometras, the cervix is open and pus discharges from the vagina; in closed pyometras, the pus cannot escape and the uterus fills. Unfortunately, pyometra is often missed by owners, particularly in cats (due to fastidious grooming), and in closed pyometras.

Untreated, it kills. It poisons the system and, if the uterus ruptures, ensuing peritonitis will cause sudden death. Fortunately, if caught early, pyometra can be treated with intensive antibiotic therapy, followed by spaying.

Prolapsed uterus

The uterus, and sometimes part of the vaginal wall, protrudes out of the cervix and is often visible outside the vaginal opening. Although it can be repaired if caught early, delay can result in sepsis, tissue death, dangerous bleeding, injury and even death. It usually occurs after birth, but can affect dogs that have never had pups.

Endometriosis and ovarian cysts or cancers 

If a female repeatedly comes on heat or has pups/kittens, the hormonal stimulation causes inflammation and thickening of the uterine lining, and mucous production. This is sometimes associated with cystic ovaries, ovarian cancer (usually highly malignant and invariably fatal), and abnormal or persistent heats.

This is uncomfortable for the animal and the excessive ‘heat behaviour’ is a nuisance to owners. Moreover, it can progress to life-threatening pyometra.

Mammary tumours

Many people are surprised to learn that animals also get ‘breast’ cancer, yet it is common in older bitches. It is rare in cats but serious when it does occur. Toy breeds are at particular risk, but owners are scared to spay too young because of their size. Malignant tumours left untreated can spread to bone, lungs or other organs and be fatal; an estimated 50% are malignant.

Spaying your pet before her first heat reduces the chances of mammary cancer by 98%. Just as with human breast cancer, lumps should always be investigated; early detection and surgical removal are crucial. By also spaying afterwards, you could prevent recurrence. Pedigreed, intentionally bred animals should be spayed as soon as their breeding ‘career’ is complete, and not too late in life.

Complications of pregnancy and birth

Almost everyone who lets their pet fall pregnant assumes that the pregnancy and birth (whelping) will be normal and easy but complications are surprisingly common, especially in ‘purebred’ animals. Accidental pregnancies and potential complications are the best reason to sterilise – and are as much the responsibility of the father animal’s owner as the mother’s.

If the pups’ mother and father are too closely related or the father is a much larger dog, foetuses can be abnormal or too big, resulting in difficult whelping, stillbirths, malformed pups, and possible agonising death for the mother. Uterine inertia (ineffective uterine contractions), mastitis (mammary gland infection), and eclampsia milk fever (a life-threatening disease caused by low blood calcium) cause great suffering, can be life-threatening, and incur considerable expense for the owner.

These are foolish risks to take if you are not a very knowledgeable professional breeder who knows all the implications (usually not the people who think they are).


Prostate infections and cancers

Enlarged prostate glands, prostate inflammation and prostatic abscesses are common in older male dogs and can become cancerous. Unlike in humans, dog prostate glands are impossible to remove surgically. Prostatitis can be treated with antibiotics and prostatic abscesses can be surgically emptied. Castration is always part of the treatment for prostatic conditions, so why not just neuter the dog as a pup and vastly reduce the chances of prostate problems?

Testicular cancers

90% of reproductive system cancers in unneutered male dogs are testicular tumours. Some are malignant and spread to the prostate gland, pelvic lymph nodes and then liver or lungs, proving fatal even after castration. Early neutering (before six months) prevents this. Although predominant in dogs over 10 years, they can affect unneutered dogs and cats of any age and breed. If you have an old, intact male dog that you are not neutering because of age-related anaesthetic risk, monitor the shape, size and consistency of his testicles closely.

Undescended testicles (cryptorchids) are prone to torsion or sertoli cell tumours, and often cause a ‘feminising syndrome’ with skin thinning and darkening, attractiveness to other male dogs, and teat enlargement. At the time of routine neutering, a vet will discover this and go looking for the retained testicle, or alert the owner to symptoms that may indicate a retained testis giving problems. It is highly unethical to breed with cryptorchid animals as it is usually hereditary.

Perianal adenoma

The third most common tumour in male dogs. This is a testosterone-dependent cancer of the glands around the anus. It starts as a small lump in the skin under the tail or next to the anus and can grow into a large, pendulous mass. Removal, combined with castration, can be curative in the early stages but older tumours may become malignant, leading to fatal invasion of the pelvic cavity and other organs.


A male animal neutered early has no testicles, almost no scrotal skin, and a small penis in a small, neat prepuce tightly tucked up against the abdomen, and does not get erections. Consequently the chances of genital injury, especially penis bone fractures, and skin cancers are greatly reduced. Neutered male dogs and cats are far less likely to scale walls, squeeze through fences, cross roads and fight with other males – all of which can end up injuring or killing them.

Stud tail

This is an area on the upper tail with hair loss or an oily seborrhoea caused by overactive skin glands stimulated by testosterone. It is seen most often in unneutered male cats and short-haired dogs. Although it usually does not hurt, it makes them smell and feel unpleasant, and in some cases, can lead to more severe deep skin infections.

Having problems with your animals that could have been prevented by simply sterilising them is like not spending money on brake pads and then wondering why you have to deal with a serious car accident. Pets adopted from welfares usually have sterilisation included in the adoption fee. Alternatively, save up or ask your vet if you can pay it off, or, if you are in a lower income bracket, contact an animal welfare organisation for help. It is the best money you will ever spend on your pet.