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 www.ratfanclub.org/books.html
These additional pages can be accessed from the sublinks above:
-A Rat Care Sheet
-Herp Owners Handout
Topics Covered on This Page:
Common Health Problems
Congestive Heart Failure
Treating Cancerous Mammary Tumors
Spinal Nerve Root Degeneration
Rat Health Insurance
For more information on rat diseases, including photos, click here.
| 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
| Eyes open
|| 2 weeks
| Weaning age
|| 4-5 weeks
| Age at puberty
|| 5-6 weeks
| Physical maturity
|| 8 months
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. 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 www.ratfanclub.org/trust.html
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
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 www.ratfanclub.org/litters.html
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
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 or two incisions should be made
at the distal end of the scrotum, not near the penis. However, care
should be taken that the incisions do 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
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.
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.
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
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
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.
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
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 more good months of life.
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.
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.
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 www.petinsurance.com or call 800-USA-PETS
For More Information
For more information www.ratfanclub.org or the booklet Rat Health Care described at www.ratfanclub.org/books.html.
All site content © 2003-2017 by Debbie Ducommun and the Rat Assistance & Teaching Society,
unless otherwise noted.
All information contained herein may be reprinted if both
author and the Rat Assistance & Teaching Society are credited.
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