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.
Physical Differences. After they reach the age of about 5 weeks, rats are easier to sex than many other small rodents. The males have obvious genitalia; the females do not. Look at the underside of your rat under the base of the tail. If you can see furry testicles, you have a boy. If you donât, sheâs a girl. Mature male rats often are substantially larger than adult females.