Anal sac disease

Anal sac problems are very common in pet dogs and something frequently seen by veterinary surgeons. In most cases, the conditions are easily treated, though they can sometimes recur. This factsheet provides information on the location and function of anal sacs as well as discussing common conditions and their treatment.

Anal sacs (sometimes referred to by vets as anal glands) are two small pockets located on either side of the dog’s bottom with openings to the surface at about the 4 and 8 o’clock positions. They produce a strongly scented substance that is deposited on the faeces and contributes to scent and territorial marking in dogs. The passage of faeces usually results in emptying of the glands in healthy dogs. The strong scent, designed to last a long time in the environment, is part of the way dogs communicate with one another.

Anal sacs may also occasionally be emptied in times of distress or panic e.g. a dog fight or a road traffic accident, resulting in a strong smell coming from the injured dog. The secretion usually has an unusual fishy odour, unpleasant to the human nose.

In this very common condition, the anal sacs fail to empty, possibly because the ducts leading to the surface are too narrow, or because the consistency of the dog’s faeces is too loose. Many dogs have anal sacs that do not empty normally. When they get very full, they can cause discomfort, usually showing as:

  • Licking the anal area excessively.
  • Sitting down abruptly and clamping the tail.
  • Dragging the bottom along the ground (‘scooting’) – often misunderstood by owners as a symptom of worms.
  • General irritability and restlessness.

The anal sacs can become infected, possibly as a result of chronic blockage (see above). If an abscess develops, the symptoms can be severe. All the signs of anal sac blockage may be present and the affected dog may be very uncomfortable and even aggressive if the hind quarters are approached or touched. The abscess may burst out to the surface, producing a foul smelling or bloody discharge. Symptoms usually ease off at this point as pressure is released and pain decreases.

In the case of straightforward blockage, periodic emptying by the veterinary surgeon is required. Some dogs need this done every 4-8 weeks; in others it is a much less frequent occurrence. Occasionally, it may be possible for an owner to learn how to perform this task, though many prefer to leave it to their vet.

Sometimes changing the composition of the diet may help. Adding more fibre to promote a bulkier stool is often recommended. It has to be said that this does not always work but is certainly worth trying.

If infection is present, a course of antibiotics may be needed. The anal sacs may also be flushed with saline or dilute antiseptic solutions under sedation or anaesthesia to help eliminate the problem. Abscesses may require surgery to aid drainage and resolution of the infection, together with a course of antibiotics and, often, painkillers.

Persistent anal sac problems may be treated by surgical removal of the anal sacs. This tends to be reserved for dogs experiencing frequent, moderate to severe problems with early recurrence after the above treatments. Removal of the anal sacs carries a small risk of incontinence due to the proximity of important nerves in the area. This may be temporary or permanent.

Much less common are tumours affecting the anal sacs. Symptoms might initially resemble full or infected anal sacs. Tumours are identified by biopsy; treatment by surgery or other means may be possible. Unfortunately, tumours in this area may prove to be malignant and ultimately life-threatening.

Anal sac problems may also be associated with another condition called anal furunculosis. As part of the treatment for that condition, removal of the anal sacs may be recommended.

How often should my dog’s anal glans be emptied?

Some dogs never need them emptied. If your dog exhibits any of the signs described above, then a check up should be arranged, but if no signs are present then the anal sacs should be left alone.

My dog seems to have a bad smell. Is it the anal sacs?

It could be, but other common conditions can also result in a bad smell e.g. ear infections, mouth infections and skin conditions. Your vet will check for these and advise on treatment.

Do anal sac problems cause constipation?

Some dogs may appear to strain, though they may not be constipated as such but just responding to irritation around their bottom area. Note that full anal sacs may occur after a bout of diarrhoea. The very loose faeces means that the sacs are not emptied as usual.