In this column veterinarian Dr Liesel van der Merwe provides practical assistance for common problems in companion animals. She is a specialist physician at the Onderstepoort animal teaching hospital and a senior lecturer in the section of small animal medicine. Send your questions to This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Dr Liesel van der Merwe

There is no evidence that an unsterilised bitch is more protective of a home or family members than a sterilised bitch. To keep an unsterilised female dog if you are not intending to breed with her has no real benefits.

A normal healthy bitch cycles twice a year. Even if she is not mated she goes into a “false pregnancy” state for about two months after her heat. Her uterus, under the effect of progesterone, the hormone of pregnancy, thus develops the glandular structure required to nourish the embryo regardless if she conceives. Repeated cycles where she doesn’t actually conceive may result in an infection of the uterus known as pyometra as the developing glands eventually become cystic.

The use of hormones to suppress her heat or delay her heat is not advised as they can potentiate a uterine infection. These hormones contain progesterone which decreases the immune response of the uterus.

This is helpful during pregnancy, as the foetus is “non-self” and the risk of “rejection” is decreased but this also makes the uterus predisposed to infection.

Early sterilisation of a bitch has also been proven to decrease her risk of developing mammary (breast) cancer. Sterilisation before the first heat showed the least risk and there was no decreased risk with sterilisation after the second heat cycle. Early sterilisation (three months) has long been practiced in the USA in their animal shelters and thus far no long-term detrimental effects have been noted. Most vets would prefer not to sterilise a bitch while she is on heat.

Castration of a male dog is a less pressing situation for most owners, as they do not have to deal with messy heat cycles. Castration is indicated if aggression towards people and other dogs and territorial urinating in the house, among other things, become problematic.

Castration in this situation should be combined with behavioural management. Early castration is necessary to remedy behavioural problems. Male dogs will generally be less aggressive if castrated. With interdog aggression, the dominant dog should be left intact and the underdog castrated to decrease his “threat” status. Uncastrated older male dogs develop prostatic enlargement by the same mechanisms as humans and may thus present with difficulty urinating, blood in the urine and constipation. Dogs with prostatic enlargement are also prone to prostatic infections. Castration will result in a decrease in the size of the prostate and is the treatment of choice.

The canine prostate surrounds the urethra, unlike in humans where it only attaches to, and surgery to debulk the prostate is not an option. Prostatic cancer does occur in dogs but is not that common.

Cats
Cats are another kettle of fish entirely. Female cats will keep on cycling every two weeks until they are mated, and they are not shy about going out and about and looking for a willing male. If no pregnancy ensues, they will once again start cycling.

They do not have the same risk for uterine infections as they do not have “false pregnancies”. Male cats wander, fight and mark furniture if not sterilised.

With the risk of contracting feline aids (Feline immunodeficiency virus – FIV) through fighting as well as the high density cat population in urban areas, there is no benefit in keeping an uncastrated male.

In both dogs and cats sterilisation will result in a predisposition to gain weight, but obesity is not inevitable, as by managing the diet and exercise this weight gain can and should be controlled.

Finally, responsible pet ownership should mean that owners do their best to avoid accidental litters as the pet welfare agencies are already crowded with unwanted dogs and cats.