Rat
Rescue :: Early
Maternal Separation
Detrimental Effects of Early Maternal Separation on Rat Pups
and Their Mothers
Biologically, rats are classified
in the class Mammalia. They are mammals. This class of animals
has more than 15,000 species, of which human beings are one.
One may define mammals as being tetrapod vertebrates which means
that they are four-limbed animals with backbones. The diagnostic
feature of the group as a whole is the possession of mammary
glands which produce milk, on which the young are fed during
the early stages of their lives. They are homeothermic or warm
blooded, having an approximately constant body temperature irrespective
of the external conditions. With few exceptions, mammals have
hairy skin and are viviparous, retaining the young in the body
of the mother during the early stages of development, and giving
birth to live young instead of laying eggs (Rowett, 1960).
As far as rat reproduction and neonatology (the study of infant
animals) is concerned, a general synopsis is provided below:
After a gestation period of between 21 and 23 days, a litter
of 6 - 15 pups is born (n = 8). During her gestation, the mother
rat will display vigorous nest-building activity, especially
in cool environmental conditions. She will carefully construct
a nest, provided she is given the materials with which to do
so. Mother rats readily tear up paper to build a nest (Weihe,
1989) which can be rather elaborate in structure (Meehan, 1984).
Rat mothers who do not have nest materials given to them will
attempt to make a nest out of whatever floor covering is available.
The nest is constructed usually in the corner of the cage or
housing facility (Fallon, 1996). Thus demonstrating a strong
maternal instinct to want to protect and nurture the young.
Nest materials serve a five-fold purpose - 1. covering to protect
the young and keep them out of sight of predators, 2. a place
of additional warmth where the temperature can be controlled,
3. a place of rest, 4. a place to rear the young and 5. a place
of food storage (Twigg, 1975; Meehan, 1984; Fallon, 1996; McDuling,
2006, in press).
The young are born pink, naked, blind, without hearing, and
unable to walk or fend for themselves, and completely helpless.
They make bird-like peeps. They are thus entirely dependent
on the mother for food and warmth (Warren, 1995; Daly, 2002).
The head is always searching with quick response to olfactory
(smell) and taste stimuli (Farris, 1950). Pups are extremely
sensitive to rearing conditions. The newborn rat is essentially
poikilothermic (unable to adjust their own body temperature),
and must rely upon the micro-environment of the nest maintained
by the mother. They rely upon the huddling of the litter to
achieve temperature regulation stability (thermal homeostasis).
Within two weeks, they are able to regulate their own temperature,
their coat develops and their eyes open (Koolhaas, 1999). They
are fed on their mother's milk until they are about three weeks
old by which time they have grown hair, can see, hear and run
about and can feed on a mixed diet similar to that of the adults
(Rowett,1960; Daly, 2002).
In addition, the new born rat lacks the ability to urinate
and defaecate on their own. The mother stimulates the pups to
do so by licking their anuses and genital regions (Daly, 2002).
If one is raising baby rats by hand, simulated maternal stimulation
of defaecation and urination must be provided (Harkness and
Wagner, 1995). One of the first acts carried out by the mother
on the newborn is licking of the anogenital region. Infants
in which this licking does not occur soon die (Meehan, 1984).
This clearly demonstrates the absolute necessity, without exception,
for the young to remain with the mother. Further, it would suggest
that pups who do not have this maternal action are subject to
much physiological stress.
Rat pups do not acquire thermoregulatory abilities (the ability
to keep themselves at constant temperature) until the end of
the first week of life. They remain in the nest and are kept
warm by each other in the nest, where they are completely covered,
and by the mother. Even adult rats display huddling behaviour
to keep warm. The litter has a high demand for heat whilst the
young are hairless (Fallon, 1996; Weihe, 1989). Harkness and
Wagner (1995) also state that young rats of less than 16 days
are easily chilled (they become hypothermic) and must be kept
warm if one is raising them by hand, to prevent the aspiration
of foodstuffs introduced into the stomach. In studies done by
McDuling (2006, in press), it was found that in addition to
warm bedding, an infra-red lamp was provided as an additional
source of heat, and placed at an appropriately safe distance
away from the young rats so as to maintain the temperature of
the internal environment at between 21º and 26º C. The actual
temperature in which rats should be housed varies. Some authors
advocate a temperature of between 18º and 22º C (Weihe, 1989)
whilst others say that a temperature of between 18º and 27º
C with an optimal room temperature of 22º C is acceptable (Harkness
and Wagner, 1995).
Mothers with normal milk production of around 10 - 20 mL/day,
usually feed the young for around an hour and then move off
the nest for a while to rest and eat, and then return to the
nest to nurture the young. A pup's body weight doubles within
five days. A fine, thin, lanugo hair occurs after day five near
the end of the first week. As the insulating fur grows, temperature
regulation becomes more efficient so that the young are less
dependent on the mother's body heat. The pups are fully covered
with a thin fur by day nine, but this is not thickly confluent
until at least day 16. Around day nine, they begin to move about
and their incisors are large enough to allow them to nibble
solids, but still need their mother's milk as additional nutrition.
Soon after this, their eyes open. At this time, the mother is
producing her maximum milk yield. Rats younger than 16 days
cannot eat solid foods as their molars have not erupted yet.
The young increase their solid consumption whilst still suckling
until they become fully independent of the mother's milk supply
at about three weeks or 21 days of age (Weihe, 1989). If suckling
stops for whatever reason, the mother's milk rapidly dries up
(Meehan, 1984).
It is thus of extreme importance that the young are left with
their mothers until at least 16 days of age, and preferably
until weaning at 21 days of age. Most authors advocate leaving
the pups with their mother until 28 days of age which ensures
better survival rate and better socialisation later on in life.
Many studies on maternal separation have been carried out,
and the results have been rather alarming. In a study by Greenberg
and Ackerman (1986), rats who were prematurely weaned at day
15 were very susceptible to developing hypothermia as well as
erosions in their stomachs (gastric erosions or ulcers). These
ulcers are highly indicative of stress. It was found that these
rats also had reduced fat stores. Fat is the tissue which, when
broken down, provides heat to the body.
Prolonged hypothermia and starvation also has a profound effect
on the infant rat's physiology and metabolism. Plasma glucagon,
glucose and free-fatty acid concentrations rose significantly
after 20 hours of induced hypothermia and starvation (Hoo-Paris,
et al, 1991). Glucagon is the hormone released when the body
undergoes a stressful stimulus such as starvation, and promotes
the breakdown of glycogen in the liver to glucose which is then
released into the bloodstream. The fact that the concentrations
of glucose and free fatty acids rose so significantly suggests
that the body was breaking down its own reserves in order to
maintain a steady state. The body was actually being broken
down, and thus deteriorating. Such deleterious changes may limit
survival time in hypothermia, and suggest that unless these
infant rats were fed and warmed, they would surely die.
Blumberg, et al (1999) found that prolonged maternal separation
inhibited endogenous heat production in infant mammals exposed
to cold. Cold can be defined as any temperature lower than that
necessary to sustain life. In work on early postnatal infant
rats who were separated from their mothers for 18 hours and
left in a relatively cold environment, it was found that the
infant rats could no longer produce any heat of their own. Heat
production or thermogenesis was inhibited and this appeared
to occur many hours before energy stores such as glucose and
fats have been fully depleted. These rats were, quite frankly,
in a state of hypothermia, and close to death. With respect
to the previous study, it would appear that the rats used by
Hoo-Paris, et al were in a state of severe deprivation.
Further studies revealed that maternal separation resulted
in a significant fall in heart rate (bradycardia) and respiratory
rate (Hofer, 1973; Hofer and Weiner, 1975). Decreases in both
heart rate and respiratory rate suggest that the animal is pre-mortem,
i.e., close to death. If infant rats are taken away from their
mothers before the appropriate weaning age when they are capable
of surviving on their own, an enormous stress is exerted on
them which could result in their ultimate death. In the study
by Hofer and Weiner, 1975, this bradycardia was reversed by
the intragastric infusion of milk. This further confirms that
starvation and maternal separation have a huge impact on the
survival of the infant rat.
As far as the mother is concerned, she is fiercely protective
of her young, and will attack and bite anyone who attempts to
intrude into the nest. She will even destroy her young if she
feels that they are threatened. The mother rat should never
be disturbed. If the cage bedding is to be changed, it should
be done with care and preferably whilst the mother is off the
nest. The young should not be touched by hands, but rather scooped
up together with the nest and placed in the clean cage. If the
young are scattered in the cage, the mother will carefully retrieve
each pup back to the nest in her mouth. (Fallon, 1996; Harkness
and Wagner, 1995).
Maternal protection of the young is a very important part of
normal rat behaviour and the mother will defend her young from
outside interference with aggression. If a nest is disturbed,
the mother will invariably build a new nest in a safer location
and move all the young to the safer location (Twigg, 1975; Meehan,
1984). Twigg in 1975 also stated that pregnant rats and rats
who have just given birth will defend their young not only from
other species, but from other rats as well.
The mother keeps the pups together in the nest. If an infant
strays from the nest, a lactating mother will readily and rapidly
retrieve it (Meehan, 1984; Koolhaas, 1999). As far back as 1933,
it was noticed that mother rats rapidly retrieved their young
when these young have either strayed from the nest or have been
taken from it (Weisner and Sheard, 1933). These authors observed
that if the young were removed from the nest for prolonged periods,
the mother rat continued to search for them for "prolonged
periods in her fruitless efforts…" They also observed that
when retrieving the young, the mother was exceptionally gentle
and deposited them in the nest with equal care. It has been
subsequently found that pup retrieval is facilitated by ultrasonic
vocalisations (sounds human ears cannot hear) sent out to the
mother by the pups who have become separated from their mother
and littermates (Koolhaas, 1999). The fact that pups call out
for their mothers when they have been separated from them is
clearly indicative of the distinct need for maternal warmth,
protection and nourishment. Furthermore, if a mother rat tirelessly
searches for her pups when they are separated from her, clearly
demonstrates maternal commitment to these pups. It is not unlike
a human child who has become separated from his/her mother and
cries for that parent, and the mother doing everything in her
power to find her child. All of this clearly demonstrates a
concern for the young and for their well-being. One might argue
that placing human qualities on animals is not scientific. However
it is becoming increasingly evident that such qualities are
universal to all animals, and that the study of animal behaviour
has been long accepted as a science since 1973. In this year,
Lorenz, Tinbergen and von Frisch were jointly awarded the Nobel
Prize for their efforts to advance the notion that animals are
indeed sentient beings, capable of a wide range of emotions
and behaviours. Since then, the field of animal behaviour or
ethology has progressed in leaps and bounds.
It is thus, in this author's opinion that separation of infant
rats from their mothers at an early age is highly detrimental
and imposes not only a great amount of stress on the infant,
but on the mother as well. Such stresses are both physiological
and behavioural. Therefore, it would be deemed to be exceedingly
cruel to forcibly separate infant rats from their mothers for
even the briefest period of time. Such separation represents
an imposition of human will on the natural behaviour and biology
of rats. This author has always gone to great lengths to simulate
the maternal environment as far as possible when hand-raising
orphaned baby rats, and to provide a stress-free environment
in which to allow these baby rats to develop. Of course, humans
cannot hear the pups calling in ultrasound, and so conditions
were provided to ensure that the babies were kept warm, well
fed, and nurtured. All of their needs were taken care of as
one would do with one's own child, and their well-being was
of the highest priority.
In conclusion, then, it may be stated that the practice of
removing infant rats from their mothers for any purpose whatsoever
should be prohibited and punishable by law. Especially should
baby rats not be used as reptile fodder as this imposes a further
stress on them. One cannot even imagine their confusion, disorientation,
separation anxiety and fear. In fact no rat or other animal
should be used as reptile fodder for the same reasons. It is
hoped that laws will soon be put in place to improve the quality
of life for animals in South Africa, and indeed throughout the
world. In this 21st Century, we should strive to make this a
better place for all concerned by the application of compassionate
science.
Author
Colleen McDuling, B.Sc(Med.Hons), MSc(Med.Sc.), Animal Behaviourist,
Scientific Representative of the South African Rat Fan Club.
References
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by Paula Spagnoletti of the South African Rat Fan Club
