All dogs have a small sac on either side of the lower margin of the anus. The sac contains a greyish, strong-smelling exudate which is discharged through ducts at the external opening of the anus.
The precise function of these structures is not understood, but they seem to be associated with the marking out of territorial boundaries and are the subject of great interest when two dogs meet for the first time.
The owner becomes aware of anal glands after some abnormality of the structures develops. When a dog is suddenly frightened or injured, the muscles around the base of the tail contract and often express the fetid contents of the glands to the outside.
Occasionally the dog may suddenly begin to lick vigorously the area beneath its tail. It may be in obvious discomfort and examination of the area may reveal an intensely red area quite swollen and painful to touch. This is caused by an acute infection of the gland, producing an abscess.
Small breeds of dogs such as poodles and terriers seem more likely to suffer this problem, possibly because the opening of the sac is quite narrow and is easily obstructed. Treatment of this uncomfortable condition involves opening the abscess, draining the infected contents and administering antibiotics.
The more common type of anal sac infection is a chronic infection of the lining of the sac, usually resulting in a thin, very foul-smelling yellow exudate. The dog attempts to relieve the irritation of the area by rubbing its anus along the lawn or carpet.
If the condition is unrelieved, the hair may be rubbed from the region and the skin may become inflamed from the constant friction.
Treatment of the chronic form of anal sacculitis involves irrigating the sac and packing it with a soothing antibiotic ointment. If this does not control the condition, consideration should be given to the surgical removal of both glands.
Many owners, when observing signs of the irritation of their pet, assume that it is caused by worms. Of course, tapeworms do cause similar symptoms but, by inspecting the feces, one should be able to see signs of tapeworm segments if the problem is due to these parasites.
Some breeders encourage owners of new puppies to regularly empty the anal glands by pinching the tissues underneath the tail between the thumb and forefinger. If done too roughly or too often such a procedure may encourage inflammation of the glands. To empty the gland, the veterinarian gently inserts a gloved and lubricated finger into the anus, everts the opening of the sac and then gently expresses the contents.
Many dogs go through life never needing any attention to the anal sacs, so that these regular attempts at emptying what is probably a perfectly normal structure may be counterproductive. The sac is naturally emptied by the stretching of the tissues when the dog is passing a normal bowel motion. Any foods which result in very soft motions or any prolonged period of diarrhea, by reducing this normal emptying of the sac, may predispose it to infections.