American Fancy Rat & Mouse Association

This article is from the Spring 1999 AFRMA Rat & Mouse Tales news-magazine.


Tumors In Rats

By Carmen Jane Booth, D.V.M.

Q I have loved rats since childhood and have one at this time for my children (so I say!). My rats have always been tumorous. The one I now have is developing tumors and her sister died 8 or 9 months ago with a huge hard tumor in her abdomen. It is really hard to see your loved animals having and dying from such a terrible disease. Other than that, I have never had an otherwise sick rat. Are there strains that are more resistant to tumors? I certainly would like to obtain such stock as pets. Laurel Bird

Q How common are tumors in rats? Our two rats are sisters (their mother died a few months ago; their father, brother and two other sisters are still living, as far as I know, in other homes). They are about a year and nine months old and overweight. We feed them hamster food, plus sunflower seeds, peanuts, and lots of table scraps. A pharmacist friend of mine says rats commonly develop tumors consisting of fat! Is this true in your experience? Our rat has a grotesque, ping-pong-ball-sized growth under one forearm. She still gets around okay, but has a little difficulty cleaning herself. If the tumor continues to grow, it will probably threaten her life, or at least make it so hard for her to move around that we’ll have to consider euthanizing her. What do you do with severely ill or malformed rats? It seems too cruel to let them suffer for long. The mother of our rats died after many months of illness. There were times when she was so distressed and uncomfortable, that if I’d known how to do it painlessly, I would have ended her life. Near the end, she would rage around the cage and try to push off the lid, all the while gasping for air. She’d let me hold her, but given the chance would tear around the house looking for a hiding place. She behaved as if she’d lost her mind. It was a sad sight. Sue Beckman

Q We have had female pet rats for the past 10 years and thoroughly enjoyed them. They all died before age 3, however, of chest tumors. (Two were operated on, but died shortly afterward.) We suspect their short lifespan is due in part to their having been bred primarily as snake food by the local pet shops. All were fairly small.

Is there a source for large female rats that aren’t prone to chest tumors? Or are there dietary secrets? (None were fed meat or sweet starches, and none were overweight.) William T. Cummings

A Tumors in rats are very common, with their short lifespan most rats will develop one of a variety of tumors as they age. There are strain and line difference in the frequency and type of tumors in inbred rats. The most common tumors in aged rats are pituitary adenomas and mammary fibroadenomas. Mammary tumors can be removed by a veterinarian (preferably when the tumor is small) and submitted for pathology to determine if they are malignant and have the potential to spread. In many instances, a rat can have multiple mammary tumors over time or have local recurrences of an aggressive tumor. You should consider the health status of the rat as well as the age before putting the animal under anesthesia. Death from anesthetic complications in old rats with respiratory disease can and does happen. In some cases where the tumor is allowed to grow too large and has severely compromised surrounding tissue such that the animal is severely debilitated, the animal may not be a safe surgical/anesthetic risk and euthanasia by your veterinarian would be the best option. In the case of the rat raging around the cage, she sounds like she had multiple problems including respiratory and neurologic, and euthanasia would have been the recommendation.

Regarding Euthanasia:

As a veterinarian I advocate humane euthanasia for any animal that is in pain or distress. No pet animal should be allowed to suffer in pain with an incurable illness. The American Veterinary Medical Association’s Panel on Euthanasia recommends carbon dioxide inhalation overdose as the humane method of euthanasia for rodents. Most veterinary hospitals do not have carbon dioxide and it can be fatal to humans if handled improperly. My professional recommendation is to deeply anesthetize the rat or mouse with the gas anesthetic on hand at the hospital. Methoxyflurane is my preference, but any will suffice. An aquarium type cage, or large jar where the animal would not be uncomfortable is preferred. Once the animal is at a surgical plane of anesthesia, I would administer an appropriate dose of euthanasia solution intracardiac (only for veterinarians experienced with this technique) or intraperitoneal. The other option is to just administer a fatal dose of inhalant anesthesia. With either method, there is no undo stress on the animal and any veterinarian can do this without difficulty. Many veterinarians with clients with multiple rats or mice will euthanize the pet for only a small fee, since in this case the time and amount of drug involved is small. *

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Updated April 2, 2014