Ovarian remnant syndrome

Ovarian remnant syndrome (ORS) occurs when ovarian tissue is left behind following neutering in female guinea pigs.

When guinea pigs are neutered, an ovariohysterectomy (when the uterus and ovaries are surgically removed) is or an oophorectomy (when just the ovaries are surgically removed) is performed. Whatever the procedure, it is important that both ovaries are removed in their entirety, as leaving behind even a very small amount of ovarian tissue will cause ORS. This can occur due to several reasons; guinea pigs have lots of internal fat and it can be difficult to visualize the ovaries amongst this. Also, as guinea pigs are not commonly spayed, some veterinarians may not be familiar with the surgical technique and in dogs and cats it has been known for them to have ‘extra’ ovarian tissue, not attached to the ovaries, so although they may be removed during a spay, it may not be noticed that this extra tissue exists.

It is very rare and there is little information available for guinea pigs due to this.

In dogs and cats, which are spayed much more frequently than guinea pigs, very few are seen, so it is not something that is commonly seen in guinea pigs and should not put you off having your guinea pig spayed if it is in their best interests.

It will only affect female guinea pigs and they will act like they are unspayed, so male guinea pigs will show a lot of interest in them and likely try and mate with her. Female guinea pigs come into season (estrous) throughout most of the year, so do not have defined seasons like dogs and cats do. Due to the increase in hormones, they can become quite agitated with other guinea pigs when in season and may also show unusual behavior such as going off food, lethargy, and bothering a companion or others in the group. Their estrous cycle lasts for 15-17 days each time, and they ovulate when mated, so the behavior may come and go, as they come in and out of estrous.

With dogs and cats it is sometimes possible to perform an ultrasound scan to look for the ovarian tissue which has been left behind, but even with dogs and cats, who are much larger than guinea pigs, this is not always possible due to the tiny amount of ovarian tissue which can be like looking for a needle in a haystack.

If an ultrasound scan isn’t possible, bloods are taken to test for an increase in female hormones when they appear to be ‘in season’, however there are two potential problems using this for guinea pigs. Firstly, guinea pigs are in season throughout the year so a spike in hormones may not be evident, and secondly, getting enough blood from a guinea pig to perform a blood test can be difficult.

With dogs and cats surgically removing the ovarian remnant is recommended, due to the behavioral signs exhibited by dogs and cats when in season, and the problems this can cause.

In guinea pigs unless the behavior is causing a problem, in a pair or group of guinea pigs it may lead to increased tension and fighting, then the necessary treatment may be less clear cut.

Putting a guinea pig through a general anesthetic is not without risk and the pros and cons should be weighed up by you and your veterinarian as to what is best for your guinea pig. The guinea pig will not be able to get pregnant if an ovariohysterectomy was performed, and this is the usual surgical procedure when spaying guinea pigs.

It may be that your veterinarian advises you to monitor your guinea pig’s behavior over the weeks and months, and if it does start to cause a problem then exploratory surgery may be recommended to see if an ovarian remnant has been left behind.

There are some incidences when spaying guinea pigs is needed, both for health and behavior reasons and the risk of ORS is so tiny that this alone should not put you off having your guinea pig spayed, if your veterinarian recommends this treatment.