Overt Gestational Changes

Once a female rat has been impregnated her entire system begins to change as her body prepares for the growth and development of her offspring. In the 21-24 days following conception there are 3 stages of pregnancy. Here we will examine the overt changes that you will see in the rat.

Overt Changes During Pregnancy

Pregnancy Stage One

  • Visual After impregnation there is not an immediate visual change. The fetuses are too undeveloped to cause a noticeable weight gain in the mother (although if weighing your female you will see weight gain).
  • Appetite
    You may begin to notice a slightly increased appetite as her body calls for more nutrition and energy to direct to the babies.
  • Behavior
    Most females do not show a marked change in behavior during the beginning of their pregnancies. However, with others you may see nipping, biting, withdrawal, or lack of energy.

The female will no longer go into heat after impregnation. The scent of a male rat will not interest her.

Pregnancy Stage Two

  • Visual
    In the second week of gestation the female will begin to fill out. Her appearance will be that of a well fed rat. Her hips may begin to widen slightly. Toward the end of the second week you may be able to feel a slight lumpiness in the abdomen, although pressing the area is not recommended as it can damage the fetuses.
  • Appetite Appetite will increase and it is very important to supply the mother rat with healthy snacks as well as with a staple nutritional food such a lab block.
  • Behavior
    No heat cycles and no interest in the scent of male rats. May sleep more, may nip on occasion.

Pregnancy Stage Three

  • Visual
    In the final week of pregnancy the pregnant female will show a dramatic change in appearance. Her weight will increase by leaps and bounds. And her abdomen will become pronounce and rounded. Some breeders describe the pre labor rat as looking like “she has swallowed a tennis ball” or “swallowed an orange.” The hips will show a definite widening. If the rat is carrying a large litter the skin may stretch to the point where the fur on her back seems thinner. You see this more often in rats with rex coats.
    Babies can now be felt by gently touching the abdomen although it can harm them if you press too hard. At the end of the pregnancy you may see movement in the abdomen as the babies reach full term.
    The nipples will become more pronounced and the fur around them will become sparse allowing the neonates easier access to them.
  • Appetite
    Females carrying a large litter may show an intense increase in appetite as their bodies divert more nutrition to feed the babies within. Healthy snacks and free feeding with a healthy staple diet is encouraged throughout the entire pregnancy.
  • Behavior
    As birth approaches your female may show signs of aggression. This will vary with each rat. Some females never show aggression during pregnancy. Others will bite and want to be left alone.
    The female may sleep more during the last week of pregnancy.

    The female usually will engage in nest building behaviors in anticipation of the pending birth.

Pregnancy Photos and Data

  • Fig. 1: Full term pregnancy photos
  • Fig. 3: (from Determining Preganancy) Pregnancy Weight Chart


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