Rats are very easy to breed. In fact, many people end up with unplanned baby
rats! Rats can reach sexual maturity at 5 weeks of age, so the sexes should be separated
at this age. Rats don’t recognize incest, so brothers and sisters and
even mothers and sons must be separated.
Rats don’t have a breeding season, although very hot or cold
temperatures will reduce breeding. Females of breeding age come into heat all
year round, every 4 to 5 days, unless they are pregnant or nursing. Each female
usually has a regular schedule that can be marked on the calendar, but it can
vary. Each heat usually begins in the evening and lasts most of the night.
As a female approaches menopause at about 18 months of age, her cycle will
become more irregular until it stops completely, and if she is bred during this
time the size of her litters will decrease as her fertility wanes. It is
possible for a female who has stopped cycling to get pregnant, although the
pregnancy may not develop normally.
You can’t count on a female being completely infertile until she
is 2 years old.
A Responsible
Decision
Before deciding to breed your rats, you should consider a few things. Do not
breed rats
who have or have had active
mycoplasma infections. You should only breed rats
who are free of respiratory symptoms and therefore hopefully
resistant to
mycoplasma. Second, rats have large
litters(average is 10 to 12) so if you don’t plan to
keep all the babies, you’ll have to decide how you will find homes for
them. Keep in mind that most pet shops sell 50-90% of their rats for reptile
food. In my opinion, the only reason to breed rats is to produce healthy, well
socialized pets with great temperaments.
Many responsible rat breeders don’t breed any female rat until she is
at least a year
old, and males until they are at least
1 ½ to 2 years old to make sure they are healthy and that the males have
no tendency for aggression.
If you
plan to breed a female a second time, it’s a good idea to wait several
weeks after her litter has been weaned to allow her to recover, both physically
and mentally!
The Mating Process
You can breed rats by simply putting a pair together for 10 days, insuring
they are together through two heat cycles. But since the female might fight the
male, a better way is to put the pair together only when the female is in heat.
This works especially well if you're breeding your rat to one who belongs to
someone else because the pair only has to be together for one evening.
When a rat is in heat her vagina will gape open; usually it is tightly
closed. Usually there will be behavioral signs too. Stroking her back will
usually cause a rat in heat to perform the mating “dance” which is
quite interesting. She may first dart forward or spin around, then she will
brace her legs stiffly, lift her head and tail, and vibrate her ears! This
display tells the male she is ready for mating.
Most males will be interested immediately and will sniff and perhaps lick
her. When mounting he will grasp her scruff with his teeth. During the
courtship, mounting will occur numerous times, but most of this is foreplay.
Usually the male must mount many times before completing the act, and mating
will continue for some time. However, it is possible for a female to get
pregnant from a single mounting, so don’t let your girls and boys play
together if you don't want them to mate. Even if the female is not in heat, a
determined and
persistant male can sometimes stimulate
her into coming into heat, so keep your
unneutered
males and females separate! Females in heat will sometimes also escape their
cage to visit a male.
Planning for the
Birth
The gestation period is normally 22 days, but can vary from 21 to 23 (and
maybe even to 25). Two weeks into the pregnancy the mother's abdomen will
usually start expanding, but not always. As the birth approaches, you may be
able to see the pups moving inside her, or feel them if you gently feel her
abdomen. The mother's needs are simple: a nutritious diet, exercise, and extra
nesting material a few days before the expected event. If you've been letting
the male live with the female you should remove him before the birth. The
father would never hurt his babies, but all females come back into heat within
24 hours of the birth (called the post partum estrus) so if you leave them
together she would immediately become pregnant again.
If the pregnant female has been living with another female, or a neutered
male, it’s all right to leave them together during the birth and the
raising of the babies, as long as the cage is large enough to allow the mother
privacy. However, it's not a good idea to leave two pregnant females together
because although they won't intentionally hurt each other’s babies, they
may steal them from each other. If this turns into a tug-of-war, the
infant’s tender skin can be severely damaged by the females’ sharp
teeth. Never put a new rat in with a pregnant or nursing female, because she
will viciously attack them.
Sometimes a pregnant or nursing rat has a change in personality from the
hormone changes. She may become more aggressive, or less interested in playing.
In rat society, a mother rat is usually dominant over all other rats, even if
she is usually submissive. However, when her job of child rearing is over, the
mother will usually regain her former status and personality. It is also common
for a nursing mom to have soft stools.
The Birth Process
The birth process normally takes about an hour or two. The first sign is a
bloody discharge from the vagina. Next, the contractions will cause her to
stretch out while her sides suck in a most amazing way. Once the babies start
arriving, the mother will sit up and help deliver them with her hands and
teeth. Then she will clean off the birth sac and lick the newborn. Each baby is
delivered attached to its own placenta. The mother will usually eat each
placenta and the umbilical cord. During this process a healthy baby will
wigggle and squeak,
which inhibits its
mother from eating it too. However, if a baby is weak or dead, this
inhibition may not occur.
Most female rats are wonderful mothers, but rarely there can be problems.
If the mother is stressed, either because of pain from a long
difficult birth, or from environmental disturbances such as unusual loud
noises, etc. she may kill and partially eat some healthy babies. A poor
diet may contribute to this problem. You can try removing the babies and giving
them back to the mom once she settles down.
After the birth is completed and the mother settles down to nurse her
litter, there is much less danger of her eating them. If you want to look at
the babies, wait until she’s off her nest and first remove her from the
cage. Some mothers will rush to defend their babies if they squeak when
handled. Don’t worry about putting your scent on the babies as this
won’t cause the mother to reject them. However, if the mother seems very
nervous, then you should look only and wait a day or two before handling the
babies. It’s a good idea to examine the babies every day to identify any
problems or remove any that have died. Rarely, on the first day the umbilical
cords will get entangled and you'll have to separate them.
Difficult Births
Birth in rats usually proceeds without need for assistance, but
occasionally, and especially in first-time moms older than 6-8 months, there
will be problems. I've seen 3 rats
who died during
birth. The danger of an obstructed birth is that the mother can go into shock.
A Caesarian section may be possible if done soon enough.
Once the birth process begins, if no babies are delivered within 2 hours,
there is definitely a problem. The rat's uterus is shaped like a Y and
sometimes a baby can get stuck across the bottom of the Y. Gently massaging the
mother's abdomen may help expel the problem baby. If a baby is stuck in the
birth canal, it may be possible to lubricate it with baby oil and pull it out
with forceps. Then the rest of the babies can usually be delivered normally or
with the aid of
oxytocin. If the mother survives the
birth with unborn fetuses, she may be able to
expell
or reabsorb them. In this case it is a good idea to treat her with antibiotics
to prevent infection.
If the mother rat does not care for her new babies, it’s possible that
her hormone levels are not where they should be. The best thing to do is
confine her with the babies in a very small cage so she will be exposed them as
much as possible, which will hopefully cause her hormones to kick in. In the
meantime, the cage should be on a heating pad to keep the babies warm. If the
mom doesn’t start caring for the babies within 12 hours, they will need
to be fostered on another mother or hand raised. (See the article about Raising
Orphans.)
Growth and Weaning
Most mom rats know just what to do and take great care of their rats.
Occasionally, there will be a tiny runt who can't compete with his siblings for
the nipples, especially in a large litter. The best solution is to temporarily
separate some of the other babies into another container to give the runt a
chance at the nipples. Leave about 4-5 babies with the runt to stimulate the
mom to suckle them. If the runt is all by
himself, the
mom may not pay attention to him. As long as the other babies are kept warm,
there is no harm in them being away from the mom for up to 4 hours. You can put
their container on a heating pad on low or near a light bulb. Keep a
thermometer next to the babies so you know exactly what temperature they are
experiencing. Use a small weather thermometer, not a medical thermometer, as
the latter can't record drops in temperature. Keep the temperature around
100-102 degrees F. Rotating the groups of babies with the mom every 2-4 hours
will give the runt the best chance.
Baby rats grow incredibly fast. I recommend you hold and look at them every day
to witness this miracle. This handling will also help stimulate and socialize
the babies. Once their eyes open at 2 weeks of age you should play with the
babies as much as possible. The more you handle them, the better socialized
they will be. At this age they'll also start to eat solid food. They'll either
walk to the dish, or their mom will carry food to the nest. You don't need to
provide any special food for them.
Babies can be weaned at 4-5 weeks, but you can leave the girls with their mom
as long as you want. Remove boys before 5 weeks or they may breed with their
mother or sisters.
Warning: If your mother has a wheel in her cage, be sure the clearance
between the wheel and the bottom of the cage is at least 1 1/2". If it is
less then this, you need to remove the wheel while the babies are 2-3 weeks
old. Otherwise, a baby can be trapped under the wheel and suffocate.
