Rat and Mouse Anatomy

Kidney Structure

• Rat kidneys contain only one papilla and one calyx.
• The right kidney is located more anteriorly than the left.

Mammary Glands

• Female rats have four to six pairs of mammary glands located in the thoracic and inguinal regions.
• In mice, mammary glands extend to the sides and back, with five pairs present.
• Male mice also have mammary glands, but nipples are insignificant.

Female Reproductive System

• The uterus is bicornuate, with each horn having a separate cervical canal.
• A membrane covers the vaginal opening until the female reaches sexual maturity.

Reproductive Cycle

• Female rats and mice are spontaneous ovulators and continuously polyestrous, with a 4- to 5-day estrous period.
• Postpartum estrus occurs in females approximately 20 to 24 hours after parturition.

Sexual Dimorphism

• Males have a larger genital papilla than females.
• Males have a greater distance between the genital papilla and anus compared to females.

Development

• Female mice develop five pairs of conspicuous nipples by approximately 9 days of age.
• Puberty in mice:
  • Occurs at around 25 days of age.
  • Complete by 50 days in males.
  • Complete by 50-60 days in females.
• Puberty in rats:
  • Occurs between 37-67 days in females.
  • Occurs between 40-75 days in males.

Breeding and Gestation

• Gestation period in mice: 19-21 days.
• Average litter size in mice: 10-12 pups.
• Gestation period in rats: approximately 22 days.
• Litter size in rats: 6-12 pups.

Pup Development

• Rat and mice pups are born:
  • Harmless.
  • Blind.
  • Deaf.
• Ears open between 3-5 days after birth.
• Eyes open between 7-14 days after birth.