The anal glands have no known function in the modern world. They are "vestigial" organs (like your appendix) meaning that they once had a function but as the dog and cat evolved, the anal glands lost that function. The best theory is that dogs once used the very pungent smelling anal gland secretion to mark their territories in the wild. Wolves and other wild cousins of the dog are known to do this. Also, dogs will occasionally express (meaning to squeeze secretion out) their anal glands when they are frightened, so it is thought the secretion may have been a defensive repellent (like a skunk).

Dogs use it primarily for territorial marking or as a form of communication. In dogs and cats, every time a stool is passed, it should put enough pressure on the anal glands that some of the secretion is deposited on the surface of the stool. Other dogs and cats are then able to tell who has been in the neighborhood, just by sniffing the stools they find. Additionally, dogs and cats recognize each other by smelling each other in the general area of the anus, since each animal’s anal glands produce a unique scent.

As the dog or cat is viewed from behind, anal glands are located on each side of and slightly below the anal opening, at the 4 'clock and 8 o'clock positions. A tiny duct or tube leads under the skin to an opening directly beside the anus

Anal Glad Problems

Anal gland impactions, infections and abscesses are very common.  For various reasons, such as the conformation of the animals, the thickness of the gland's secretions or the softness of the stool, these glands and their ducts often become clogged, or impacted. When this occurs, the animal will sit down on its rear quarters and drag its butt across the floor or ground. This is called scooting. Both dogs and cats may lick the anal area excessively. Impacted anal glands are a very common problem for a lot of dogs, especially the smaller breeds. 

The problem is that pets may injure the anal area when scooting across the ground, or discharge the secretion on the carpet or floor. And this material has a terrible odor. 

Anal glands may also become infected and abscess. Bacteria make their way into the glands, probably through the ducts. This is a very painful condition.  The first sign you may see is that the animal cries when you touch the area near the tail, or when attempting to defecate 

Contributing Factors

The main factors which predispose our pets to have problems are (1) small body size and (2) obesity. Dogs under 20 lbs. have a higher incidence of anal gland problems than larger dogs. The smaller the dog is, the more chance of anal gland problems. Teacup poodles, Chihuahuas, and Pomeranians have an unusually high incidence of impaction. As with all generalities, of course, we will see exceptions with many small dogs never having any anal gland problems and some large dogs occasionally having severe problems. Overweight dogs can have a mechanical problem with getting the glands to express well.  

Treatment and Prevention

When the glands become impacted, they must be cleaned out, or expressed. Pet owners can do this themselves, especially after being shown how. This empties the glands of all material. It is done by applying pressure with the finger, starting behind the gland and then pushing outwards. In some dogs this may need to be done every week or two.  

Anal gland abscesses require surgical treatment, and antibiotics are usually given to the pet. Using warm compresses on the area often helps to relieve some of the pain and reduce swelling.

If an individual pet only has an occasional problem with the gland, they can be dealt with as needed. For pets with repeated or chronic problems, surgical removal of the glands may be recommended.  Although removal is a fairly straight- forward procedure, complications such as fecal incontinence can rarely occur.

Pets with recurrent anal gland impactions are often placed on a high fiber diet. The high fiber makes the animal's stool more bulky. The stool will put more pressure on the anal glands and hopefully the glands will express themselves when the animal defecates.