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.
The rat attains sexual maturity early in life and the new born are dependent upon the mother, rats therefore have well developed nests with the new born being weaned after 3 - 4 weeks. The litter size does vary but an average litter size is 8 with approximately 6 litters per annum.he rat attains sexual maturity early in life and the new born are dependent upon the mother, rats therefore have well developed nests with the new born being weaned after 3 - 4 weeks. The litter size does vary but an average litter size is 8 with approximately 6 litters per annum.