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.
1 A litter of six to ten young are born after a gestation period of about three weeks. 2  Young rats are weaned at around 20 days of age and can breed at three to four months of age.  Younger rats will mate in the same location in which they were born or will migrate to a new, unoccupied territory.