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.
Female mice come into estrus (heat) every 4-5 days (this is the time they will be fertile and receptive to a male). They will have a fertile estrus within 12-28 hours after giving birth, and within a couple of days of weaning a litter. Length of Pregnancy: The gestation period of mice is usually 19-21 days.Note: mice can breed shortly after giving birth. If they breed while already nursing a litter, the gestation period can be longer (around 28 days).Litter Size:Litter size is quite variable; 7-12 pups per litter is considered average but more is not unusual (20 in a litter is quite possible).ote: mice can breed shortly after giving birth. If they breed while already nursing a litter, the gestation period can be longer (around 28 days). Litter Size: Litter size is quite variable; 7-12 pups per litter is considered average but more is not unusual (20 in a litter is quite possible).