Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

A reader wrote complaining that one of her dogs regularly releases anal sac content whereas the other does not.

The anal sacs are found at about four o’clock and eight o’clock on each side of dogs’ and cats’ anuses. The sac has a glandular lining which secretes a smelly greyish brown liquid or pasty substance. These are scent glands and the secretions are used for territorial marking.

This is especially evident in the territorial behaviour of hyenas and wild dogs where objects such as trees and stumps are sprayed with this secretion. It is no longer prevalent in our domesticated dogs and cats. Normally a small amount of this secretion is expressed whenever the dog or cat defecates, thus “marking” the stool. Dogs do not spray scent glands directly to mark territory.

Dogs and cats do, however, expel their anal sac content when scared or in a fight or accident, which results in a characteristic foul fishy odour.

The size of the sacs and amount and thickness of the secretions vary among individuals. The amount of material passed normally during defecation also depends on the formation of a nice firm stool. Soft stool will not exert enough pressure on the sac to cause expression. Poor rectal sphincter muscle tone, being female, and obesity predispose to anal sac problems. Each animal is different.

In my opinion anal sacs are like wisdom teeth – they do not really have any function in the domesticated animal and if causing problems should be removed. When overfull, anal sacs can inspissate (where the contents can become dried and hard) and they can also become infected. Blocked and infected or abscessed anal sacs are very uncomfortable for the pet.

This condition seems to affect the smaller and medium breeds more frequently than large breed dogs. Symptoms which require investigation include: scooting, licking under the tail and chasing the tail (in dogs that are too fat to reach there), reluctance to sit, fresh blood on the faeces, swelling and redness around the anus and straining to defecate.

If your dog is prone to having blocked anal sacs you can either have them regularly expressed as a preventative measure or you can have them removed. I had my dog’s anal sacs removed when she was 18 months old as I could not stand the foul fishy smelling breath.

The operation is delicate, as the rectal nerves run nearby, but if performed carefully, it has no complications besides mild incontinence for about a week post operatively. Once the gland has ruptured or developed an abscess it is a bit harder to locate and remove all the glandular material.

The anus is also surrounded by seven different types of anal glands. These are not related to the anal sacs but can develop into benign and malignant tumours. The anal sac may also become cancerous and develop into a malignant tumour in females, although not as commonly in males.

Cats in general have fewer problems with their anal sacs but can develop blocked sacs and abscesses