Post partum (after birth) maternal behaviors in the female rat are primarily brought on by hormonal changes in estrogen, progesterone, oxytocin, and prolactin. Environmental factors, individual line issues, and physiological factors can alter, disrupt, or inhibit these normal behaviors.
Exposure to babies will maintain maternal behaviors and the removal of the offspring will cause it to decline. It is important to note that attentive and nurturing maternal behaviors can make a big difference in the learning abilities and well being of a litter. According to studies, babies that receive more “loving” attention show higher levels of brain development than those raised by indifferent mothers.(Meany, 2000)
Maternal behavior can be broken down into several categories such as: birth behavior, care of infants, suckling behavior, human interaction, and also negative maternal behavior.
Mom and You
It is important to mention first that the mother rat may not be receptive to having you near her offspring. This sometimes will be very intense at birth and will taper off as the babies get older.
Maternal aggression towards humans is going to vary from rat to rat. With some mothers aggression is totally nonexistent and mom will let you handle babies with no stress or biting. Other moms may get very aggressive and will attack and/or bite.
During the first week after birth the babies do not need to be checked or handled very often. If the mother is aggressive you can distract her or lure her out of the cage with food while you quickly check, count, or photograph the offspring.
To avoid injury, be sure to approach any female with a new litter with great care.
Some factors that can affect maternal aggression:
- Genetics (certain lines show higher maternal aggression)
- Socialization of mother
- Number of litters the mother has already had
- Environmental Stress (noise, movement, etc.)
- Bonding between handler and mother
- Health of mother
As the mother rat begins to give birth her level of estrogen increases and progesterone declines. Research has shown that even though these hormonal changes help in facilitating maternal behavior, it is actually the increase of oxytocin that brings on rapid onset of maternal behavior.
During labor the mother will move around and then either lay or crouch as each pup is born. She then cleans her vulva, gently removes the birth sac from the newborn, and licks the pup.
The mother rat will then ingest the placenta. This is known as placentophagy and is a healthy practice used by most mammalian mothers. The placenta contains high levels of prostaglandin which stimulates involution of the uterus and small amounts of oxytocin which eases birth stress and stimulates lactation.
Care of Infants
Once the babies are all born the mother will generally retrieve all of them and put them in the nest where she can keep them warm and safe. She will usually pick them up by the nape of the neck or the back.
At times a nursing pup will get dragged from the nest as the mother is exiting and dropped outside. The mother generally will notice this and return it to the nest. If a mother does not notice, you can carefully return the pup to the nest or place it at the opening of the nest for retrieval.
Once the babies eyes are open and they are walking the mother generally will not actively retrieve them.
There are several different licking behaviors that you see the mother perform on the babies. The first is licking the body to clean and nurture the babies. The second is anogenital licking which stimulates the pup to urinate and defecate. Without this stimulation waste would build up in the system and the pup would not be able to survive.
In early handling of short duration the mother will lick the babies as soon as they are returned to her. If the time the babies are separated is lengthy the mother may show reduced attention to them and not lick them much, if at all.
After the babies are born the mother will hover over the litter making her nipples accessible to them. Due to the fact that newborns may suckle up to 18 hours a day, the mother will spend quite a bit of time in the nest in the first week after birth. During initial nursing bouts you may see the mother licking and rearranging the babies before she settles in to let them feed.
Once the litter reaches 14-15 days old their eyes are opening and they are able to eat portions of her food. The mother is spending less time in the nest nursing them. You may see mothers, during the third-fourth week, trying their best to escape the increasing demands of their offspring.
At times a mother rat may move her litter from place to place within her environment. Usually this is due to stress and/or perceived danger. She is likely trying to locate an area for her litter that she feels is safe. Often this behavior will occur after the babies have been handled or after cage cleaning.
If a mother is moving the entire litter try to leave her alone and reduce environmental stressors such as noise and activity. Keep in mind that the constant relocating of the babies may cause injury. You may want to remove hammocks and tubes to insure that the mother does put the babies in a high place where they may fall and be injured.
It is not unusual for a female with a large litter to split the babies into 2 piles and nurse them separately. This behavior will actually give all of the offspring a chance to feed. The female rat typically has 12 nipples. In a larger litter (13-22) the female rat may be able to ensure more offspring survive by splitting them up. You will need to check both nests to make sure that she is feeding each group sufficiently.
The Darker Side of Maternal Behavior
Not every rat is going to follow the typical birth behaviors. And although some behaviors may be alarming, all behaviors do have rationality whether or not we understand..
Scattering is the act of leaving babies strewn away from the nest. It is hypothesized that this may be a behavior as we see in wild rats when the litter is threatened. According to that theory, a predator would be attracted to, and snatch, the scattered babies while leaving the rest of the nest unharmed. Some moms tend to accidentally scatter their babies as they leave the nest to feed and drink.
Placing the babies back in the nest and making sure the surroundings are quiet and stress free may help to eliminate this maternal behavior.
Disfigurement and Injury of Neonates
Occasionally a check of a new born litter reveals babies that are bitten, missing partial limbs, or sections of their tails. This is referred to as birth trauma. Often this is a result of the mother assisting in a pup’s birth by pulling on it with her teeth.
Some mothers will accidentally damage their babies while they are removing the birth sac or during retrieval and carrying.
Babies can also be harmed by the mother if she is in with another rat who is stealing the babies or if she is highly stressed.
Litter abandonment can occur for several different reasons. The foremost reason is that the mother is unable to lactate and/or is lacking maternal drive.
Babies from these litters can be fostered by another mother who has a new litter. A mother with an older litter may not accept them, and even if she does, will be lacking the initial colostrum that they need. These babies may, however, be supplemented with a simulated colostrum formula. Another option, if there is no foster mother, is to hand feed the litter. This is difficult and time consuming. Generally the rate of survival for hand raised rat neonates is very low.
Individual Pup Abandonment
It is always alarming when an individual pup is singled out and abandoned. Unless there is something obviously wrong, the confusing part is trying to determine why. All too often we have seen offspring who were incredibly runted or maimed that the mother still fed and cared for. In the fancy we have seen babies with genetic diseases that the mother never abandoned.
It does not seem that having “something wrong” with the pup is enough to lead to abandonment. It may be that the mother senses the pup’s eminent death, is culling her own litter to make it manageable, or has some unknown aversion to the pup.
Sometime a foster mother will take an abandoned pup in or an owner can hand raise it.
Post Mortem Cannibalism
It is not uncommon for a mother rat to consume a stillborn pup or one that has died after birth. This usually occurs in the first few days after birth. It may be a way of keeping the nest “clean” or the mother may perceive the dead pup as a high protein meal.
Not all mothers cannibalize dead offspring. Some will simply push the body to the side of the nest or remove it and place it somewhere else within the cage. Others will keep the dead pup in the nest with the live ones.
The term infanticide is defined as the killing of an infant. It is hard to determine, unless you actually witness it, whether or not a female has committed infanticide or if the pup has died naturally.
It is not typical for mother to kill their own offspring. Mother rats may kill the offspring of other females and virgin females will often kill babies (suggesting that hormones play an active role in determining female behavior to offspring). Yet there certainly are scenarios when mothers kill their own.
Some hairless mothers who are unable to lactate may kill their entire litter. Hairless females with diminished lactation may cull their own litter one by one until they reach the number of babies that they can provide nourishment for.
Typically infanticide is committed during the first few days of life and the killing of an individual pup is more likely than the killing of an entire litter.
Some factors that may lead to maternal infanticide include: hormonal imbalances, environmental stress, hunger, protein deficiencies, vitamin deficiencies, and obesity.
For more information see the Rat Behavior article: Infanticide in Norway Rats
- Ingestion of Afterbirth Appears to Promote Maternal Behavior in Mammals. (2005, February 11). Retrieved December 18, 2008, from http://www.buffalo.edu/news/fast-execute.cgi/article-page.html?article=71210009.
- Peters, L., & Kristal, M. (1983). Suppression of infanticide in mother rats. J Comp Psychol, 97(2), 167-77. Retrieved December 18, 2008, from the Medline database.