Key Points About Rats

Here is a brief summary of the information we have found to be most helpful for Veterinary Personnel. More complete information on health issues, including drug dosages, can be found in the booklet Rat Health Care by Debbie "The Rat Lady" Ducommun. More complete information on rat care and behavior can be found in the book Rats, also by Debbie Ducommun. Both can be ordered from The Rat Fan Club at

These additional pages can be accessed from the sublinks above:

-A Rat Care Sheet
-Herp Owners Handout

For more information on rat diseases, including photos, click here.

Rat Facts

Average life span - 2 to 3 years
Maximum life span - 7 years 1 month (Guiness Book of Records)
Estrus cycle - Every 4-5 days, and immediately after giving birth
Gestation period - 21 to 23 days, 28 days for a post partum pregnancy
Average litter size - 12
Eyes open - 2 weeks
Weaning age - 4-5 weeks
Age at puberty - 5-6 weeks
Physical maturity - 8 months

Rat Behavior

There are a few rat behaviors that are sometimes mistaken for health problems. One of these is when a rat stares into space, swaying or weaving his head back and forth. This behavior is most common in pink-eyed rats and means the rat has poor eyesight. Moving their head back and forth helps their depth perception through a phenomenon called parallax. As they sway back and forth, closer objects seem to move more than objects farther away.

A female rat in heat can become jumpy, especially when touched on the back. When touched, she may also arch her back and vibrate her ears! Female rats in heat can be quite determined and inventive in reaching a male rat, for instance, leaping huge distances or squirming through cage bars, and must be securely confined.

About 5% of male rats get aggressive when they reach full maturity, and sometimes this behavior change can occur as young as 4-5 months or as late as 18 months. These males can become aggressive to their cagemates, inflicting quite severe lacerations on their roommates' bellies or groins. They can also become aggressive to humans, biting them to express dominance. The only solution to this behavior problem is to have the male neutered. Once the testicles are removed testosterone levels immediately drop, but the aggressive behavior can persist for up to 12 weeks (probably because the brain must reorganize.) However, neutering will eventually be 100% effective in eliminating aggressive behavior toward humans and 90% effective in eliminating aggression toward other rats. Neutering will also reduce urine marking behavior.

Domestic rats are true domesticated animals and are born tame, but they still need to be socialized to bond to humans. Baby rats need to handled as much as possible beginning at birth and especially between 2 and 4 weeks of age to make sure they will be friendly and calm. It is a myth that handling the babies will cause the mother to kill them.

Rats who were not properly socialized as babies will often exhibit fear toward humans. But even most of these rats can be quickly rehabilitated using a method called Trust Training. This technique uses soft food on a spoon as both a lure and reward for desired behavior. For more info on this technique go to


Rats are highly social animals and do best with a cagemate. A single rat can become insecure and nervous. Studies have also shown that single rats tend to get sick more than rats in groups. We recommend that rats be kept in same-sex or altered pairs or groups. As long as the rats are properly socialized, they will still enjoy interacting with their owner. A single rat must have several hours of human interaction every day.

Rats need a cage large enough to provide room for toys and exercise. Minimum should be 14" X 12" X 24" but bigger is better. Rats also need a place to hide and sleep such as a box or a hammock. Toys are not optional, they are required for the rats' health and well-being. They enjoy climbing toys such as ladders, branches, concrete blocks, and ropes as well as tubes and boxes. A large exercise wheel is highly recommended as most rats really enjoy running on a wheel. 

Pine and cedar shavings should not be used in rat cages because they contain acids that damage the respiratory tract. This is especially dangerous since the most common health problems in rats are respiratory infections. Pine and cedar shavings also contain toxic phenols that are absorbed into the blood. Studies show that long term exposure can cause an enlarged liver, altered immune response and decreased fertility and litter size. (If you would like a copy of these studies please let us know.) You will find a list of safe alternative beddings at

The best commercial food for rats are rat blocks or nuggets. These food pellets supply a complete and balanced diet. A fortified grain mix can also be used, but many rats will pick out and eat only their favorite bits leading to an imbalanced diet and wasted food. Their diet should also include a variety of fresh fruits and vegetables.

Baby rats should be weaned no earlier than 4 weeks, and waiting until 5 weeks is better. At 5 weeks the males and females must be separated because some rats become sexually mature at this age and pregnancies can result.

Rat Neuters and Spays

A rat spay is similar to a cat spay and can significantly reduce the incidence of mammary and pituitary tumors. Neutering a male rat does not provide any significant health benefits, but it will reduce urine marking behavior, atypical aggression, and normal secondary sexual characteristics such as rougher coat and heavy oil production from the skin on the back.

Surgery on rats requires special attention to anesthesia, body temperature control, and analgesia. Only gas anesthetic should be used on rats. Injectable anesthetics cannot be controlled carefully enough. Extreme caution must also be used with pre-anesthetics. The patient must be kept warm during and after the surgery. Rats physically can't vomit, so there is no need to withhold food and water before the surgery, and because the rat's metabolism is so fast, doing so can compromise recovery.

For a rat neuter, one incision should be made at the distal end of the scrotum, not near the penis. However, care should be taken that the incision does not extend to the anus. The testicles should be removed using a closed method, since rats have an open inguinal canal, with careful ligation of the large testicular artery. A scrotal abscess a few weeks after a neuter is a common complication due to a reaction to the sutures. This usually resolves on its own.

After a rat is spayed or neutered, most patients experience abdominal cramping so pain relief is imperative, and sometimes necessary up to 3 days later with neuters. I personally find that buprenophine is much more effective than Metacam for this purpose.

Nursing Care

The best nutritional supplement for sick rats is powdered soy baby formula, which can be mixed as thick or thin as needed. Rats will also often take foul-tasting medications in it. It is best to try to get rats to take their medications willingly by mixing them into a tasty liquid or food. However, medications can be forced by putting only 0.1 ml at a time in the back of the throat.

The best place to give injections to a rat is in the loose belly skin in front of the hind leg. The skin at the nape is ten times thicker. All injections can be given subcutaneously.

Common Health Problems

The most common health problems in rats are bacterial respiratory infections and congestive heart failure. In female rats, benign mammary and pituitary tumors are extremely common. The other most common problems include injuries, abscesses, spinal nerve root degeneration, external parasites, cancers, pododermatitis, and malocclusion. Rats have a brownish-red pigment in their tears called porphyrin and the excessive discharge of this matter from the eyes or nose is a common non-specific sign that can be caused by respiratory disease, stress, or eye irritation.


Rats usually heal quickly due to their fast metabolism, and often veterinary treatment is not needed for injuries. Lacerations - even if subdermal - up to 1 ½" long do not need suturing. Closed fractures of the leg - even if comminuted - usually heal well on their own. Degloving of the tail is a natural response and the damaged tail normally does not need to be amputated. The exposed tissue will dry up and fall off on its own in a few weeks. Treatment is needed only if infection or self-mutilation occurs.

Severe swelling of a foot due to injury does need treatment as it will tend to get worse due to compression of the veins. One injection of dexamethasone at 2.2 mg/kg will usually be sufficient. Ibuprofen can also be given at 132 mg/kg twice a day.


Abscesses are a common occurrence in rats and most abscesses on the body will open, drain and resolve on their own. Males are particularly prone to abscesses in the groin. Abscesses on the face can be much more serious. An abscess on the face or under the ear that does not quickly heal after being drained is most likely caused by a cancer such as squamous cell carcinoma or zymbals gland cancer.

Respiratory Disease

The underlying cause of respiratory disease in rats is infection with the bacteria Mycoplasma pulmonis. This disease is extremely contagious and is transmitted from mother to offspring shortly after birth. Pretty much all pet rats in the United States and England now have it, whether or not they have symptoms, and it is incurable, although aggressive antibiotic treatment can keep it under control. Mycoplasmosis makes the rats more susceptible to frequent secondary bacterial infections as well. It can also cause uterine bleeding.

Antibiotics in the penicillin family, such as amoxicillin, tend to work best against secondary infections and are the best first treatment, especially in younger rats. Secondary infections can quickly become acute and fatal so should be treated first. The actual mycoplasma infection is a chronic, more slowly advancing disease.

If there is no improvement within the first 2-3 days of treatment, another antibiotic should be tried. In cases of severe acute infections, the recommended treatment is with both amoxicillin and enrofloxacin at 22 mg/kg twice a day. When a treatment is effective, antibiotics for a secondary infection should be continued for at least 2-3 weeks, to prevent relapse. Enrofloxacin and/or doxycycline are the recommended treatments for mycoplasma, and treatment should continue for at least 6-12 weeks and often lifetime treatment is necessary. These antibiotics can be used long-term without any danger. (One of my vet's patients was a rat who lived 4 years, and was on enrofloxacin the last 2 years of her life.)

In older rats with chronic respiratory disease, it usually becomes necessary at some point to also use drugs such as a bronchodilator, diuretic and anti-inflammatory. The drugs I have used with excellent success are aminophylline at 5.5 mg/kg 2-5 times a day either orally or by subcutaneous injection, furosemide at 2-10 mg/kg twice a day, and prednisone at 2 mg/kg twice a day. A subcutaneous injection of dexamethasone at 2 mg/kg can often work wonders in acute cases.

There are two viruses that can cause respiratory symptoms in rats. Sendai virus causes a true respiratory infection but is quite rare. Slightly more common is the sialodacryoadenitis (SDA) virus which infects the salivary glands, and symptoms can include sneezing, wheezing, runny eyes and nose, labored breathing, swelling of the glands under the throat, bulging eyes and sudden death. SDA virus is most commonly picked up at a rat show.

Of course there is no treatment for the virus, but affected rats can get severe secondary bacterial infections that can be fatal. Sometimes treatment with amoxicillin and/or enrofloxacin is enough, and sometimes gentamicin with either amoxicillin or cefadroxil is necessary. Aggressive supportive therapy, including fluids, and dexamethasone for inflammation, might be necessary. Both viruses will die out in a population within 30-60 days if there are no new rats or babies. Charles Rivers Laboratories says the SDA virus is only shed for 7 days, but an infected rat will usually have antibodies to the virus for the rest of her life.

Congestive Heart Failure

Signs of respiratory disease, such as wheezing and labored breathing, can also be caused by heart failure. It is common for an older rat to have both respiratory and heart disease. It is also possible for younger rats to have heart failure. In cases of respiratory symptoms where serial treatment with several different antibiotics results in only temporary improvement, congestive heart failure is probable. Fortunately, many cases of heart disease can be successfully controlled with drugs. Enalapril at 0.5 mg/kg twice a day or another ACE-inhibiter can be used to diagnose heart failure in rats. If symptoms improve after 1-3 days of treatment then the rat has heart failure.

The most common type of congestive heart failure in rats is hypertrophic cardiomyopathy. Treatment with an ACE-inhibitor and a beta-blocker, and sometimes also a diuretic and/or bronchodialator can be very helpful. I have successfully used enalapril, atenolol (2.2 mg/kg twice a day), furosemide (2-6 mg/kg twice a day), and aminophylline (5-10 mg/kg 2-5 times a day) in lots of rats with heart failure.

Rats can also have dilated cardiomyopathy. This form of heart disease can be very successfully treated with the treatments mentioned above as well as digoxin at 0.0055 mg/kg twice a day.

Mammary Tumors

About half of all intact female rats will develop benign mammary tumors, and it is common for a rat to get multiple and serial tumors. These tumors are easily removed by minor surgery. Large incisions can be protected with a body cast made of tape. Cancerous mammary tumors are more rare and probably only occur in 5% or less of female rats. Mammary tumors can occur in male rats but are relatively rare.

Pituitary Tumors

Pituitary tumors, which are always fatal, occur in 16-20% of intact female rats and in about 7% of male rats. Early signs are usually loss of general coordination and/or loss of dexterity of the front legs. These symptoms usually progress over a period of a few weeks to a few months. A diagnostic symptom is when the rat cannot bend her front legs to hold food to the mouth. Other signs can include walking in circles, hyperactivity and running into objects. Eventually the neurological deficits will progress to the mouth and the rat will have difficulty eating. Treatment with amoxicillin and with prednisone at 2.2 mg/kg twice a day will often shrink the tumor and slow its growth. Cabergoline at a dose of 0.6 mg/kg is very effective in most cases and has given many rats up to 8-12 more good months of life.

Tumor Prevention

Studies show that having female rats spayed when young reduces the incidence of mammary tumors from 50% to 4% and pituitary tumors from 16% to 4%. The best time to spay a rat is between 3-6 months, with the earlier the better. Unlike dogs, who must be spayed before their first heat cycle for the full benefit of breast cancer prevention, spaying rats at any age can help prevent mammary tumors. (It would be very difficult to spay a rat before her first heat because they can come in heat as early as 5 weeks of age!) For full protection from pituitary tumors, a rat should be spayed before 6 months.

Treating Cancerous Mammary Tumors

The vast majority of mammary tumors in rats are benign. Benign adenomas usually have a somewhat rounded shape and a low blood supply and are therefore light in color. Malignant mammary tumors have a much higher blood supply and can usually be easily diagnosed by their darker appearance, even through the skin. Malignant tumors also remain flat rather than protuberant. Surgery is not effective for malignant mammary tumors, but fortunately tamoxifen is an effective treatment. Tamoxifen works in rats by blocking the estrogen receptor sites in the tissue. It can shrink the tumors or slow their growth for many months. The recommended dose is 6.6 mg/kg once a day for the rest of the rat's life. Many rats start refusing the medication after a while, however, benefits can continue, and after a month most rats will be willing to take the tamoxifen again.

Other Tumors

Fibromas tend to be fairly common in male rats, usually occur on the side and can usually be removed easily. In my experience the only type of cancer that can be temporarily treated surgically is fibrosarcoma. Debulking sugeries for these tumors can often be successfully repeated several times. For other cancers, surgery tends to cause the tumor to grow more quickly and can often result in an open wound that won't heal. Treatment with prednisone at 2.2 mg/kg twice a day can slow the growth of some tumors, most notably adenocarcinoma of the pituitary gland, various brain tumors, and bone cancer of the jaw.

Spinal Nerve Root Degeneration

This is a common problem in older rats. The back legs get progressively weaker and weaker over a period of weeks or months. A more sudden paralysis will usually be caused by an injury, a stroke, a blood clot in the spinal cord, or a pituitary or brain tumor that has hemorrhaged. The cause of the spinal nerve root degeneration is unknown, but supplementation with liquid B vitamins can often slow the progression of the paralysis, especially when started early. Give enough of a liquid B complex to supply 5 mcg of B12 once or twice a day.

External Parasites

The two most common external parasites in rats are lice (Polyplax spinulosa) and fur mites (Radfordia ensifera). The species specific lice are visible and often do not cause signs. They can be treated with oral ivermectin at 220-440 mcg/kg once a week for 3 weeks, or one dose of selamectin or moxidectin..

Fur mites are also species specific, are microscopic and live in the hair follicles. Skin scrapings can often be negative even when mites are present. Rats can harbor these mites without signs, but when signs occur they include puritis and self-inflicted wounds indicated by scabs on the shoulders, neck, throat or chin. In the United States ivermectin used to be effective for fur mites but they are now immune to it. The only effective treatment for rat fur mites now is one dose of selemectin at 13 mg/kg, or one dose of moxidectin at 2.2 mg/kg.

Please note that fipronil is extremely toxic to rats when taken internally and should be used only with caution, and does not seem to work for fur mites anyway.
Less common are rat mange mites (Notoedres muris) which cause lesions on the ears and sometimes the tail, and can be treated like fur mites. Tropical rat mites (Lyponyssus bacoti), which will also bite humans, must be treated with one dose of selemectin at 26 mg/kg.


Commonly called bumblefoot, this is an infection in the bottom of the heel. It can appear as a red swelling or a yellowish ulcer. It is usually caused by irritation from wire cage floors, and tends to be worse in overweight rats. It also seems to run in families. Oral antibiotics do not seem to help. The most effective treatment is daily application of a horse remedy called Blu-Kote which contains these active ingredients: Sodium propionate, gentian violet, acriflavine, in a special base of water, urea, glycerine, isopropyl alcohol 47% by volume.


Rats have open-rooted incisors which grow continuously. They normally wear against each other, but when malocclusion, or other tooth disease, occurs the teeth can grow long enough to cause injury and difficulty eating. The incisors can be easily trimmed. Rat molars are close-rooted.


Intracardiac injection is acceptable only when performed on heavily sedated, anesthetized, or comatose animals. (The 2000 Report of the AVMA Panel on Euthanasia) For rats in respiratory distress, inhalant anesthesia without sedation is the only recommended method as sedation can increase respiratory distress.

For rats who aren't in respiratory distress, the method I like is to give a sedative (administered either orally or by subcutaneous injection) followed by euthanasia solution administered by intraperitoneal injection, which will allow the owner to hold the rat and comfort her as she falls unconscious. This method takes about 10-20 minutes, and disturbing behavior almost never occurs as the rat passes through stages I and II of anesthesia.

One of the best ways to learn about the successful treatment of rats is to do as many gross necropsies as possible. Consider offering to do them free for your rat-owning clients.

Rat Health Insurance

The Veterinary Pet Insurance company offers major medical policies for almost any type of animal. This policy can make more extensive health care, such as mammary tumor removals and diagnosis and treatment of heart failure, affordable. For more info go to or call 800-USA-PETS

For More Information

For more information or the booklet Rat Health Care described at

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All information contained herein may be reprinted if both author and the Rat Assistance & Teaching Society are credited.
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