Breeding Age

  • Breeding age of female (optimum): 3-10 months
  • Breeding age of male (optimum): 3-24 months
  • Sexually mature: 5-6 weeks of age

Female Statistics

  • Type of estrus: polyestrous (heat at fairly regular times- year round)
  • Frequency of estrus: Every 4-5 days
  • Length of estrus: Usually 12 hours (most often at night)
  • Return of estrus after delivery: 12-24 hours
  • Female menopause (estropause): 18 months (variable, but most common 15-18 months)
  • Pelvic fusing in females: No
  • Number of teats on a female: 12
  • Number of uteruses: 2 (“uterine horns”)

Pregnancy and Babies

  • Gestation: 21-23 days
  • Weaning age: 21-28 days
  • Average litter size: 6-12 (variable from 1-22)
  • Average size of newborn: 6-7 grams
  • Fur on babies: 7-10 days
  • Eyes open: 12-15 days
  • Ear canal open: 12-14 days
  • Descent of testes: 15-50 days


The Rat Guide and its affiliates accept no responsibility for misuse or misunderstanding of its information. This guide in whole or part, exists solely for the purpose of recognizing and understanding the care and illnesses in the pet rat. Please seek advice and treatment from a qualified Veterinarian if your rat is ill.

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