Macarthur Veterinary Group
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Anal Sac Disease

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Anal Sac Disease is quite common in dogs and occurs occasionally in cats. It is the most common cause of ‘scooting’ behaviour - where a dog drags its bottom along the ground.

What are anal sacs?

Anal sacs (sometimes called anal glands) are small sacs just under the skin on either side of your dog’s anus at the 4 o’clock and 8 o’clock positions. They connect to the anus by means of small canals or ducts. (In cats the ducts open on the skin just beside the anus). The sacs contain a really foul-smelling liquid, much worse than poo!

What are anal sacs for?

Their purpose is not known for certain but there are several theories:

  • The smell from the sacs has a role in territorial marking in wild animals. Wild dogs rub their bottoms on vertical structures such as trees to spread their scent. This behaviour is not commonly seen in domestic pets.
  • The sacs are often partly emptied as the dog goes to the toilet. This may also help with territorial marking.
  • The smell helps in social recognition between dogs, which may be why they sniff each other's bottoms!
  • The sacs are also emptied when the dog is frightened, similar to the behaviour shown by a skunk to scare away its enemies. Some believe that this may have been the original purpose of the anal sacs.

What causes anal sac disease?

The causes are not well understood. It's thought that in our pet dogs, the sacs are rarely emptied properly. The fluid builds up, solidifies, and becomes an ideal environment for bacteria to grow. Anal sac disease may be associated with soft faeces, a recent bout of diarrhoea, or certain skin diseases. Small breeds and overweight dogs are more likely to get anal sac disease.

Symptoms: If you see your dog scooting along on their bottom, it means they have some type of irritation around their rear end. This can be due to fleas, dermatitis or occasionally tapeworms, but the most common cause is full, impacted or infected anal sacs.

Attempts to pass a motion (poo) may cause pain. As a result, your pet may not go to the toilet as often as it should and constipation can occur.

If an infection develops pus or blood may sometimes be seen. Your dog or cat may also lick its bottom and show other signs of pain. Left untreated, the sacs can rupture and an abscess will develop around the anus. This will be seen as a red painful swelling, often with an open sore at the centre.

Tumours can also occur in the anal sacs.

Sometimes dogs will leave a foul-smelling drop of liquid where they have been sitting. Some dogs are born with anal ducts that do not close well, resulting in a constant discharge of anal sac fluid, and a recurrent bad smell!


Impacted anal sacs can be emptied by your vet and this will usually solve the problem. We do this by placing a gloved finger inside your dog’s anus and gently squeezing the discharge out. Not a pleasant task!

In some cases, the problem can recur and repeated emptying is needed. We can show you how to do this yourself - but few people take us up on this offer! Sometimes the secretion is too thick to squeeze out or it may be too painful. In such cases, the sacs may have to be emptied under anaesthetic.

Infected anal sacs result when bacteria grow inside the sacs, and this can be more difficult to treat. The sacs are emptied (sometimes repeatedly) by squeezing them, as described above. They may need to be flushed and cleaned under anaesthetic. Antibiotics will be given (either tablets or an ointment directly into the anal sacs) and possibly some pain-relievers as well.

Surgery: If repeated severe anal sac disease occurs, we may suggest surgical removal of the sacs. This is also the only way to treat those dogs that have anal sac tumours or a constant discharge of smelly anal sac fluid. Complications can occur. If the nerves around the anus are damaged, your dog may lose control of their bowels and drop poo without being aware of it. This is usually temporary but can be permanent.


Diet considerations: Changing your dog’s diet may be useful. The goal is to make your dog’s droppings more bulky so that the anal sacs are squeezed more often as they go to the toilet. This is done by increasing the fibre in the diet by adding bran or grated carrot.

Obesity increases the risk of anal sac disease (along with many other diseases), so weight loss is important. Low-fat prescription diets that are used for weight loss are also high in fibre. Follow the links below for advice on diets and weight loss.