Guinea Lynx A Medical and Care Guide for Guinea Pigs


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Impaction in Boars

Older boars may develop a condition called impaction. The muscles of these guinea pigs have weakened and they are no longer able to expel the soft caecal pellets that accumulate in the perineal sack. But you can help! Andrew's advice will guide you through the maintenance process.

Typical boar

The following article was contributed by Andrew and printed with his permission. While not all boars will develop impaction, knowing what to look for and a little preventive maintenance will keep your animal healthy. Wonder if you have a boar or sow? Check photos and advice on sexing your pigs, if you are unsure.

Thanks to Paul Livingston (reprinted with permission) have been added for clarity. Top two photos: typical boars. Third and fourth photos: the perineal sac.

And thanks to Brimstone and Paulo Ferraretto for their wonderful photos.

Anal Impaction

Photo of boar Guinea Pigs are coprophagic which means they eat their own droppings as part of their normal digestive process. In most cases, they are selective, eating only the smaller, moister droppings, which they usually take directly from the anus. Perhaps you have watched your guinea pig in a crouch position, patiently waiting and then suddenly reaching down to eat a pellet.

These lighter, softer pellets are called caecal faeces and are very important to your guinea pig's health because they contain important B-complex vitamins. Caecal pellets are trapped on their way out of the rectum in an area called the perineal sac and the larger, harder fecal pellets are pushed out.

Anatomy lesson

Perineal Sac (below) and penis (above) When you tip you guinea pig up you will see the folds of the anus. If you gently pull the folds apart you should notice two parts:

  • The PERINEAL SAC which is actually 95% of the area and contains a sticky fluid produced from two small glands;
  • The RECTUM which is a small opening where both the caecal pellets and normal fecal pellets are expelled from the digestive tract.

In older BOARS, (rarely younger and rarely in females because the sac is much smaller) the muscles of the anus stretch/weaken and the boar is no longer able to properly expel the fecal pellets from the anus. Both caecal and fecal pellets become trapped or impacted in the perineal sac. If left unchecked, your boar will begin to lose physical condition because he is no longer able to eat the caecal pellets and the blockage interferes with the normal digestive process.

Perineal sacIf this condition develops, it's necessary to clear the impaction every day. To accomplish this, flip your guinea pig on his back and smear a small amount of mineral oil inside the anus. Gently push down on the bottom side of the anus and ease the impacted mass out. Sometimes your guinea pig will ingest some of these pellets if you feed them to him, however, more often than not, you will have to supplement his diet with vitamin B-complex (25mg per day dissolved in water, applied by syringe).

A Regular Routine (no matter what age)

The perineal sac is a collecting place for all sorts of debris (hair, cage shavings, hay) and should be checked on a regular basis and cleaned if needed. Warm water soaks can help make removal of hardened material easier (Q-tips work well). Gently retract the folds of the anus to ensure that all debris has been completely removed. See a vet if you are unsure!

Regular checking of all males is recommended. Check more frequently if a particular guinea pig has problems often.


A good diet with lots of hay and a large cage to encourage exercise (with an energetic companion) will help keep your boars healthy. If your current bedding (shavings, paper products) collect in your boar's sac, changing to fleece bedding may also help. Find a discussion of impaction experiences in the forum.


"Since Rocky's sac is so leathery it requires more frequent monitoring and cleaning. First I remove any accumulation by either using Q-tips (for a small amount) or opening the sac and gently coaxing out the impaction (for larger amounts such as that pictured). Next I rinse his sac with warm water using a large syringe (6cc). The water rinse does a much better job of removing all the gunk from the wrinkles and crevices than Q-tips and mineral oil. After rinsing thoroughly I coat his sac with mineral oil (per Pinta's suggestion) to minimize the build-up. I rinse his sac once or twice a week, as needed. I open his sac to remove accumulated feces on an almost daily basis. Living with a younger and more energetic cagemate has forced Rocky to move more and keeps his butt cleaner. I don't know Rocky's exact age, but I estimate he was at least 5 when these pictures were taken."

Brimstone contributed the following pics to help illustrate how she takes care of her boar, Rocky. Click on the photo for a larger image.

First photo is the before photo. Second photo, Brimstone opens the sac to gently remove the impacted material:

  • "Because of Rocky's lack of elasticity this is fairly easy to do. We do this for him most days."
Impaction, before.             Impaction, checking the anal sack.

Two views of how to rinse using a 6cc syringe and warm water:

Impaction, rinsing.             Impaction, rinsing.


"This is what Rocky's sac looks like when it's inverted. There's some slight swelling on the left side of the picture, which according to my vet is normal in older boars with this type of problem. There's a yellowish part in the middle that's the most "leathery" part of his sac."

Inverted anal sack.


Brimstone also sent a couple pictures of her normal boar, Apollo, who was about 14 months when these were taken. The pictures followed a general cleaning (removing hair and other debris, no impaction issues) with mineral oil, which gives the sac a wet appearance.

Brimstone suggests trimming rump hair on a long-haired boar before a general cleaning. "It will be much easier to find his sac under all the hair!"

Male guinea pig reproductive organs.             Male guinea pig reproductive organs.

Brimstone's videos are also very helpful. Check out her Guinea Lynx post for comments and links to them.


After examining the anal sack, examine the penis and clean any debris you find. The whitish material is called smegma and may be odorous. Cold pressed coconut oil is excellent for softening stubborn dirt and debris. Apply and let sit for 20-30 minutes before gently wiping off. Then clean gently with warm water and lubricate the penis with mineral oil or cold pressed coconut oil. If you find any raw skin or sores, apply a thin film of antibiotic ointment.

On occasion, ejaculate can harden within the penis, which can cause great discomfort. Ejaculate is generally white and appears rubbery. It is commonly referred to as "boar glue".

To extend the penis, press down gently (first photo). Second photo shows the penis with the prepuce drawn back. Click on the photo for a larger image.

Extended             Prepuce drawn back.

Thanks to Paulo Ferraretto for his crisp photos.


Gastric Transit Time. The food a guinea pig eats, generally leaves its stomach in a couple hours. Start to finish averages 20 hours and can vary from 8 to 30 hours, according to Hillyer and Quesenberry's book. This does not include coprophagy, which would extend the time until the food completely leaves the system to 66 hours.

Coprophagy (eating the soft cecal feces) is vital to the good health of all guinea pigs as it provides them with necessary nutrients. Guinea pigs may eat the soft cecal feces 150 to 200 times in a day, usually directly from the anus. If an animal is obese or pregnant, these soft droppings may be expelled and eaten from the floor. Very young guinea pigs may also eat their mother's soft droppings. Some guinea pigs have been known to snatch cecal feces from other pigs. These feces are supposedly the best ones to feed a sick guinea pig on antibiotics in order to reinoculate good bacteria into the digestive system. The drier fecal pellets are also used but do not contain as many beneficial bacteria.

In his book A Grown-up's Guide to Guinea Pigs, Dale Sigler suggests that guinea pigs on high protein diets produce more cecal feces. Encouraging grass hay consumption and cutting back on starchy foods like carrots may help. And as a last resort, neutering.

Neutering is a surgical procedure and all surgical procedures carry real risks, even when performed by an experienced vet. If you consider this last option, make absolutely sure you have located a vet with extensive experience and a good track record to minimize the possibility of losing your pet during the surgery (problems with anesthetics) or recovery (infections).

  • Anal impaction is most often encountered in older boars, unusual in females. Occasionally young boars may develop an impaction.
  • In older boars, this may be caused by loss of muscle tone or difficulty in removing the pellets. In some guinea pigs, the harder pellets can still be expelled.
  • Impaction in younger boars can be due to marking habits and personal hygiene.
  • Boars that have been neutered rarely if ever experience impaction.
  • Routine examination of the anal area will help prevent problems from affecting the health of your boar.
  • A few older boars may require daily cleaning of the perineal sac. Periodic occasional cleaning may also be beneficial for boars that are not impacted. Exercise care in removing any debris and do not pull anything out forcibly. Instead, soften the matter until it can safely be removed.
  • If your guinea pig reingests the pellets, mineral oil is the best lubricant to use for cleaning purposes. Go Up

"Constipation" Molitity issues in guinea pigs are not referred to as "constipation".

  • Male guinea pigs may become impacted(described on this page).
  • A guinea pig that is not passing feces may be eating too little food.
  • A guinea pig may have an intestinal blockage or another medical condition.

If your guinea pig is ill, be sure to see a vet. Provide your guinea pig with a good diet which includes unlimited high quality hay to keep that food moving!

See Pet Education's article on Cecotropes and Coprophagy explaining this unique method of digestion employed by rabbits, guinea pigs, and a few other rodents and mammals.

More information can be found at Peter Gurney's site and half way down the page at the Dale Sigler's Cavy Care site and by Chris Wheeler who suggests that:

    "Whenever you pick up a boar, rest your hand under his rump so that you can feel the testicles, if he is starting to get impacted you should feel a hardness within the pouch.

    "Gently separate the testicles so that the inside of the pouch is visible, if the boar is impacted, a firm dark lump of matter can be seen. If not, the inside of the pouch will be lined with the natural whitish paste called cecum." Go Up

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