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.
Rats normally leave their litter at 6 weeks of age; they are fully weaned from their mother at 4-5 weeks, but benefit greatly from staying with their breeder and being socialised until 6 weeks, since the period from 2-6 weeks of age is a crucial stage in the rat's mental and social development.