Benji, a six year old male Shih Tzu who started “scooting” his rear end along the ground.

The Hanley family knew that there was something strange going on with Benji. For no particular reason, he had started rubbing his rear end along the ground. He looked as if he was sitting down, and then he pulled himself along with his front legs. This was peculiar behaviour when he did it outside on the grass, and at first the Hanleys thought it might just be an odd thing that dogs do from time to time. But when Benji started to do it indoors, on the carpets, it was definitely time to take him to the vet to find out what was going on.

As I listened to the description of what was happening, I knew at once what was going on. This “rear end rubbing” is a common complaint. Many owners refer to it as “scooting” or “sledging”, and people often think that it is caused by worms. It is true that there are worms that can cause an irritation under the tail, and it does make sense to check that a recent worm dose has been given. But the most common cause of the problem is a “dog” thing that thankfully, humans don’t suffer from: anal sac disease.

Dogs, cats, and many other animals have two small anal sacs which produce a strong smelling glandular secretion. The sacs, one on the left and one on the right, are hidden beneath the skin, and they are each connected by a duct to the lower bowel, just inside the anus. Every time the animal passes a motion, the anal sac is physically squeezed out, so that their secretion is applied to the outside of the faecal pellets. The anal sac secretion smells disgusting to humans, but it carries very important messages in the animal world. The concept of “territory” is an essential part of animals’ social lives, and anal sac scent deposits are one of the ways that dogs leave a mark to let other dogs know that they have been around.

The skunk has particularly well-developed anal sacs, which they are able to control with voluntary muscles. The strong stink associated with skunks is due to their ability to turn around and drench enemies with the contents of their anal sacs.

Fortunately, dogs do not use their anal sacs in this way. Instead, the anal sacs are usually an invisible part of a dog’s anatomy that is not apparent to an owner. Occasionally, for different reasons, the anal sacs can become diseased, and the scooting behaviour is the most obvious sign that something has gone wrong.

The most common problem is simple: the anal sacs stop emptying properly, and become over-full. They are normally around the size of a raisin, but they can expand to the size of a large grape. There are different reasons whey they may not empty properly, but the most common one is that modern pet food is not bulky enough to enable the sacs to be squeezed out effectively. In the wild, dogs eat fur, skin, bones and all sorts of other non-digestible matter that passes straight through their digestive system. As a result, their faecal pellets tend to be large, with a firm consistency, and they are very effective at squeezing out the anal sacs. Pet dogs tend to eat highly processed food that creates softer, smaller faecal pellets that are not as good at emptying the anal sacs. In many dogs there is not a problem: the anal sacs still somehow empty effectively. However in some individuals, the sacs fill up with secretion, and when they become swollen, they start to be itchy. This is why dogs like Benji start to scoot along the ground. Sometimes the scooting behaviour solves the problem: some dogs are able to naturally empty their own anal sacs by doing this. But in most cases, human intervention is needed to sort things out.

Emptying over-full anal sacs is probably the most unpleasant job that I need to do as a pet vet. Latex gloves are essential. The area around the anus is squeezed firmly, and the accumulation of anal sac fluid is physically emptied onto a piece of cotton wool. The latex glove is then discarded into a sealed clinical waste bin. The smell of anal sac secretions is strong, musky and disgusting, similar to the stench of a skunk. There are occasional incidents where the secretion squirts in the wrong direction, escaping confinement within the latex glove. If this happens, it can leave a foul smell on your hands, or on your clothing, that is exceptionally difficult to remove.

In most cases, the anal sacs only need to be emptied once. Benji’s owners have been given instructions to add a teaspoonful of bran to his diet every day, and hopefully this will prevent the problem from recurring. Occasionally, dogs can suffer from repeated anal sac problems. They can become infected, and more complex treatments are needed, such as flushing under anaesthesia, with long courses of antibiotics. Rarely, the anal sacs cause such severe ongoing problems that they need to be surgically removed.

Benji did not enjoy having his anal sacs squeezed out any more than I enjoyed doing it. We are both hoping that this was a one-off incident. The Hanleys have started adding bran to his diet, and with luck, the problem has been permanently solved.


“Sledging” or “scooting” is often a sign of anal sac problems

Affected animals usually need to have their anal sacs squeezed out by the vet

Additional fibre in the diet can prevent recurrence of anal sac problems

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Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.

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