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What Are Anal Sacs In Dogs And Cats?

Does your dog scoot, turn and lick at the base of his tail, or show discomfort when passing stool?  Fleas are a possibility, itchy skin, too; but any one of these behaviors could be a sign of anal sac disease.  Anal sacs or anal glands…whatever you call them they sure can be a source of discomfort and even serious infection in your dog.  Find out what these mysterious little structures are up to.

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 Learn all about these mysterious structures.

by T. J. Dunn, DVM

“You think it’s his what?” asked the incredulous owner of the uncomfortable Basset Hound on the exam table.  I restated my diagnosis, knowing the owner probably never heard the term anal sacs before.  “Barkley has an anal sac infection.  See how swollen and inflamed it is next to his anus.  In fact the abscess is nearly ready to break through to the surface of the skin.   We’ll need to open this abscess and allow the infection to drain, and then we’ll flush it, check the other anal sac, and send him home on antibiotics.  Warm compresses for a few days will speed up the healing, too.”

Few topics raise dog owners’ eyebrows (and lower dogs’ tails) faster than the subject of anal sacs.  Often called anal glands, these two small repositories of foul smelling material technically are not glands at all.  Rather they are sacs or pouches lined with cells whose job it is to continually produce an oily semi-liquid substance that is stored within the sac.  It accumulates like water in a reservoir until pressure on the sac forces the contents through a narrow opening just inside the anus.  Whenever I describe these unpopular structures to the dog owner, invariably I’m asked  “What the heck are they for?’  For a credible response I draw on my extensive knowledge of comparative anatomy, pathology, microbiology and biochemistry and respond, “I have no idea”.

Anal sacs are small paired pockets located between the internal and external anal sphincter muscles, one on each side of the anus at the 4 and 8 o’clock position.  The sac empties through a short and narrow duct to the surface near the edge of the rectum and skin at the anus.  Each sac is lined with abundant sebaceous (oil) glands and numerous apocrine (sweat) glands.  The secreted substance is a semi-oily, brownish fluid that packs an odor strong enough to gag a maggot!

One study indicated that anal sac disorders affects about 12% of dogs. There are a number of theories why dogs, cats, skunks, and other mammals have anal sacs and what possible use they may have.  One theory states that anal sac contents, when excreted with the passing stool or by anal sphincter muscle contraction, act as a powerful territorial scent marker somewhat akin to humans posting a No Trespassing sign.  Another theory states that the anal sac material lubricates hard stool, which makes passage easier.  Humans do not have anal sacs.  It’s bad enough that some humans get hemorrhoids, which are dilated, irritated blood vessels at the anus; luckily, dogs do not get hemorrhoids. 

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analsacs_ivanesthesia analsac_abscess analsacs dogs analsacs_dogs
Anal sac abscesses require anesthesia and surgery to eliminate the infected and damaged tissue An abscess of the right anal sac just before it was going to rupture Some anal sacs can be felt and emptied (expressed) by careful external pressure This image shows the location of the anal sac opening and some slightly dry but normal anal sac material

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There are no predictable antecedents to painful anal sac disorders.  Infections, obstruction and subsequent overfilling (called impaction), and rupture with drainage through the perianal skin are the most common clinical presentations.  Anal sphincter muscle dysfunction, enlarged anal sacs that are not compressed properly by the anal sphincter muscle, hypersecretion from the anal sac lining, obstructed or constricted anal sac ducts all may be predisposing circumstances for anal sac problems.

This Bassett has an abscessed right anal sac.Some dogs may be born with very narrow channels that lead from the sacs to the edge of the anus, thereby obstruction the flow of anal sac material.  Acquired damage to the duct can occur when perianal infections, trauma, allergies and inflammation compress or obstruct the narrow channel leading from the sac to the surface.  For unknown reasons some dogs produce a thick or dry material from the sac lining which makes passage of the material through the narrow ducts impossible. 

There is no age or sex predisposition to anal sac pathology.  Uncommon in large breeds, infections and impactions are often experienced by small breeds such as Toy and Miniature Poodles, Chihuahuas, and Lhasa Apsos.  Cocker Spaniels, Basset Hounds, and Beagles rank high on the list of breeds affected by anal sac difficulties.

Some groomers and animal health care workers believe feeding a diet rich in fiber aids in emptying the sacs. The pressure of the firm stool against the colon wall near the anus may help to express the anal sac contents.  Dogs that have an existing problem such as infection or obstructed ducts, though, probably won’t respond to dietary changes; modifying the diet with more or less fiber yields inconsistent benefits. 

There is a difference of opinion regarding routine expressing of the anal sacs.  For example, veterinarian Mark Thompson in his presentation about anal sacs in Current Veterinary Therapy XIII, This is the location of the left anal sac of a dogsuggests routine manual expressing of the anal sacs should not be done in a normal dog with no anal sac issues.  Many groomers make it a matter of routine, though, to express the anal sacs of their dogs.  Certified Master Groomer Sherri Glass, for example, has been grooming dogs for 14 years and has taught grooming for 5 years at Cornerstone Dog Grooming Academy in Clyde, OH.  She relates, “I teach students to empty anal glands on all small dogs, about 20 pounds or less in size.  We also do any size dog at owners request.  If dog owners would meet their dogs nutritional needs with high quality food, keep them at proper weight, and provide plenty of good exercise, most dogs would not have to have the anal sacs expressed.”   Mr. Jeffrey Reynolds, Director of the National Dog Groomers Association of America says “In states were it is legal for groomers to express anal sacs, many groomers express them externally only either as a part of the grooming procedure or at the owners request. When This image displays normal paste-like material being expressed from the left anal sac.there is evidence that the sacs are impacted, then they are not expressed and the owner is advised to bring the dog to the vet.” 

There is an 88 percent chance the thought of anal sacs will never even occur to you.  However, if your dog is one of the 12 percent that scoots his rear bumper along the carpet, frequently turns to lick or bite at the base of his tail or anal region, or displays discomfort when passing stool, it would be advisable to make an appointment with the veterinarian.  If left untreated, anal sac impactions, infections and abscesses can be a reoccurring nuisance for your dog so be proactive about an evaluation if your dog displays any discomfort in the tail or anal region.

“Do-it-yourself-anal-sac-expressing” can be done at home once your veterinarian has instructed you.  (Yuck… be careful about contact with anal sac secretions or you’ll be very unpopular with yourself and others!)  Some cases respond to infusion of the sacs with antibiotics in addition to oral medication.  In chronic cases, careful surgical removal of the anal sacs can be curative; the dog never has another annoying bout of anal sac disease.  Be sure to discuss the pros and cons of surgery if chronic problems lead you in that direction.

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