The anal glands or anal sacs are small glands near the anus in many mammals, including dogs and cats. They are paired sacs on either side of the anus between the external and internal sphincter muscles. Sebaceous glands within the lining secrete a liquid that is used for identification of members within a species. These sacs are found in many carnivorans, including wolves, bears, sea otters and kinkajous.
The anal glands are in the wall of the anal canal. They secrete into the anal canal via anal ducts which open into the anal crypts along the level of the dentate line. The glands are at varying depths in the anal canal wall, some between the layers of the internal and external sphincter (the intersphincteric plane). The cryptoglandular theory states that obstruction of these ducts, presumably by accumulation of foreign material (e.g. fecal bacterial plugging) in the crypts, may lead to perianal abscess and fistula formation.
In dogs, these sacs (anal glands) are occasionally referred to as "scent glands", because they enable the animals to mark their territory and identify other dogs. For most dogs the anal glands will empty a small amount of fluid each time the dog passes faeces. But sometimes the anal glands do not empty naturally or do not empty enough and this can lead to the glands filling up and becoming uncomfortable, leaking at inconvenient times or even becoming impacted and infected if left untreated.
A dog with an anal gland problem may drag their bottom along the floor (scoot) or try to bite at their bottom. You may notice a strong fishy smell on your soft furnishings or coming from your dog’s bottom. Your dog may even stop wagging their tail, seem depressed, or object to their tail being handled or lifted. There is a common misconception that a dog will drag his bottom along the floor when he has worms. In reality, it is most likely to be because of full anal sacs.
If your dog is showing signs of anal gland problems, always see a veterinary professional. It is important to be sure of the issue before poking or squeezing anal glands or you could do more harm than good. If your vet diagnoses an anal gland problem that is infrequent and not complicated by infection, they can quite easily express the anal fluid. It is a relatively simple 2-3 minute procedure. If there is infection or the glands are blocked, a course of antibiotics may be required before the sacs can be emptied.
If the problem is frequent and not complicated by infection, you can empty your dog’s anal sacs yourself, with a little patience and know-how. A good vet will be happy to give you some instructions on how to do this or you can get advice online. But please take care. A lot of instructions advocate ‘squeezing’ the anal glands. Squeezing too hard can cause your dog a lot of pain and make things worse.
If your dog has frequent issues with their anal glands not emptying naturally, schedule a reminder to check your dog’s anal glands regularly (say once a month) and empty them whenever they feel full.
Discomfort may also be evident with impaction or infection of the anal glands. Anal sac impaction results from blockage of the duct leading from the gland to the opening. The sac is usually non-painful and swollen. Anal sac infection results in pain, swelling, and sometimes abscessation and fever. Treatment often involves frequent expression of the sac and systemic antibiotics. Occasionally treatment may include, lancing of an abscess or antibiotic infusion into the gland in the case of infection. The most common bacterial isolates from anal gland infection are E. coli, Enterococcus faecalis, Clostridium perfringens, and Proteus species.
Anal sacs may be removed surgically in a procedure known as anal sacculectomy. This is usually done in the case of recurrent infection or because of the presence of an anal sac adenocarcinoma, a malignant tumor. Potential complications include fecal incontinence (especially when both glands are removed), tenesmus from stricture or scar formation, and persistent draining fistulae.
Anal sac fluid varies from yellow to tan or even brown in color and watery to could be kind of thick in consistency, yet still easily expressible. Impacted anal glands can be identified by the material usually being very thick, most times gritty or not being able to express anal sacs altogether without serious pain or damage. The presence of blood or pus indicates infection.
As with dogs, a cat's anal glands can spontaneously empty, especially under times of stress, and create a very sudden unpleasant change in the odor of the cat. A cat's glands may become impacted, causing the cat to defecate outside the litter box, almost anywhere in the house. A veterinarian can empty the clogged glands, and defecating outside the litter box will stop immediately in most cases. Often this problem is incorrectly interpreted as behavioral, when it is entirely a problem of clogged or blocked anal glands or difficulty defecating.
Opossums use their anal glands when they "play possum". As the opossum mimics death, the glands secrete a foul-smelling liquid, suggesting the opossum is rotting. Note that opossums are not members of the carnivora, and that their anal sacs differ from those of dogs and their relatives.
Skunks use their anal glands to spray a foul-smelling and sticky fluid as a defense against predators.
An extraction of castoreum, the scent glands from the male and female beaver is used in perfumery and as a flavor ingredient.
- L. David Mech; Luigi Boitani (1 October 2010). Wolves: Behavior, Ecology, and Conservation. University of Chicago Press. ISBN 978-0-226-51698-1.
- Rosell, F.; Jojola, S. M.; Ingdal, K.; Lassen, B. A.; Swenson, J. E.; Arnemo, J. M.; Zedrosser, A. (Feb 2011). "Brown bears possess anal sacs and secretions may code for sex". Journal of Zoology. 283 (2): 143–152. doi:10.1111/j.1469-7998.2010.00754.x.
- Dyce, K.M.; Sack, W.O.; Wensing, C.J.G. (1987). Textbook of Veterinary Anatomy. W.B. Saunders Company. ISBN 0-7216-1332-2.
- Kenyon, Karl W. (1969). The Sea Otter in the Eastern Pacific Ocean. Washington, D.C.: U.S. Bureau of Sport Fisheries and Wildlife.
- Ford, L. S.; Hoffman, R. S. (1988-12-27). "Potos flavus". Mammalian Species. American Society of Mammalogists. 321: 1–9. doi:10.2307/3504086. JSTOR 3504086.
- Yamada, Tadataka; Alpers, David H.; Kalloo, Anthony N.; Kaplowitz, Neil; Owyang, Chung; Powell, Don W., eds. (2009). Textbook of gastroenterology (5th ed.). Chichester, West Sussex: Blackwell Pub. ISBN 978-1-4051-6911-0.
- Wolff, Bruce G.; Pemberton, John H.; Wexner, Steven D.; Fleshman, James W.; Beck, David E., eds. (2007). The ASCRS textbook of colon and rectal surgery. New York: Springer. ISBN 0-387-24846-3.
- Ettinger, Stephen J.; Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3.
- Hill LM, Smeak DD (2002). "Open versus closed bilateral anal sacculectomy for treatment of non-neoplastic anal sac disease in dogs: 95 cases (1969–1994)". J Am Vet Med Assoc. 221 (5): 662–5. doi:10.2460/javma.2002.221.662. PMID 12216905.