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 Old World rats breed year-round, but reproduction is concentrated in the warmer months. 2  A litter of six to ten young are born after a gestation period of about three weeks.  Young rats are weaned at around 20 days of age and can breed at three to four months of age.