The stomach has three types of contractions: There are rhythmic, 3 per minute, synchronized contractions in the lower part of the stomach, which create waves of food particles and juice which splash against a closed sphincter muscle (the pyloric sphincter) to grind the food into small particles.
7 What is the gestation period, how many babies do they have, and when are they weaned? 1  The gestation period for rats is 19â22 days, for mice it is 17â21 days.  Rats and mice average 8â12 babies in a litter, but can have as few as 1 or as many as 20.
This has led to recommendations of early breeding to avoid endangering the mother rat. There is no scientific evidence that rats experience pelvic fusing at any age. In the laboratory the traditional breeding age begins at 3-4 months and ends at 10-12 months. Maximum fertility is reached at between 3-10 months.s they age their reproductive organs will become less suited for pregnancy and birth and the eggs will become less viable. Male rats can impregnate a female as young as 5 weeks, although that is not common. They are able to breed for most of their lives.