By T. J. Dunn, Jr., DVM
Few topics raise dog owners’ eyebrows (and lower dogs’ tails) faster than the subject of anal glands. These two small structures are renowned for the foul-smelling material they produce, but what is their purpose and what should pet parents do when something goes wrong with them?
What Are Anal Glands?
Anal glands, or anal sacs as they are sometimes called, are small paired pouches located between the internal and external anal sphincter muscles, one on each side of the anus at roughly the 4 and 8 o’clock position. They empty through short and narrow ducts just inside the anus. Each sac is lined with abundant, modified sebaceous (oil) and apocrine (sweat) glands. The secreted substance is normally an oily, brownish fluid that packs a strong odor.
Liquid held inside the sac is usually expelled when a dog defecates, but if this does not occur on a regular basis, the material inside thickens, which makes it harder to pass. If this situation persists, the gland may become impacted, inflamed, and infected. The gland can even abscess and rupture through to the skin surface.
What Do Anal Glands Do?
There are a number of theories why dogs, cats, and other mammals have anal glands and what possible use they may have. One states that anal sac contents, when excreted with the passing stool or by anal sphincter muscle contraction, act as a powerful territorial scent marker. Another theory states that the anal sac material lubricates hard stool, which makes passage easier.
Causes of Anal Gland Problems
One study indicated that anal gland disorders affect about 12 percent of dogs. Problems are seen less frequently in cats, but they are still possible. It is often difficult to determine why some pets suffer painful anal sac disorders while others do not. Obese animals do seem to have more trouble with their anal glands than do slimmer individuals, probably because extra body fat in the anal region lessens the pressure that passing feces applies to the glands. Similarly, pets who have chronically soft stools tend to be at higher risk of anal gland problems. Some individuals may be born with very narrow ducts that drain the glands, thereby obstructing the flow of anal sac material. Acquired damage to the duct can occur with perianal infections, trauma, allergies, or inflammation. Other potential causes include anal sphincter muscle dysfunction, distended anal glands, and overproduction of anal gland material.
Relatively uncommon in cats and large breed dogs, anal gland infections and impactions are more often diagnosed in small breeds such as Toy and Miniature Poodles, Chihuahuas, and Lhasa Apsos. Cocker Spaniels, Basset Hounds, and Beagles also rank high on the list of breeds affected by anal gland difficulties. Dogs of any age and either sex can be affected.
The Role of Diet
While a change in diet alone won’t resolve a significant anal gland problem once it has developed, feeding a diet rich in fiber may help prevent future recurrences. The pressure of the firm, bulky stool against the colon wall near the anus can help to express the anal gland contents when a pet defecates.