Rat Reproduction - Anatomy & Physiology

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  • Penis is easily extruded from the prepuce.
  • Os penis lies within the tissue of the penis.


  • Two testes in an external scrotum.
  • Testes descend between day 30-40.
  • Open inguinal canals throughout life.
    • Allows the testes to shrink and return to the abdomen during the non-breeding season.
  • Head and tail of the epididymis are the sites of extremely large fat pads.

Accessory Sex Glands

Rats have highly developed accessory sex glands. These produce a gelatinous copulatory plug, which is visible in the vagina post-mating and is thought to prevent semen leaking out.

Seminal Vesicles

  • Lie dorsolateral to the urinary bladder in contact with the rectum dorsally.
  • Large and lobated, opening into the lower end of the ductus deferens.
  • Each is enclosed in a capsule together with the coagulating gland.

Prostate Gland

  • Bilateral and has three lobes: the dorsal, lateral and ventral.
  • Dorsal is known as the Coagulating Gland.
  • Lies close to the seminal vesicle.

Ampullary Glands

  • The glands of the ductus deferens.
  • Lie near the bladder.

Bulbourethral Glands

  • Found near the urethra as it exits the pelvis.

Preputial Glands

  • Lie in the subcutaneous fat near the penis and open into the prepuce.
  • Sebacious glands that secrete a pheromone used for scent marking.
  • Regress with age and fill with stagnant sebum.

Puberty and Sexual Maturity

  • Sexually mature at 6-8 weeks

Mammary Gland

  • Teats are absent.


Reproductive tract


  • Right ovary is located at the level of L4-5 just caudal to the right kidney.
  • Left ovary is located at the level of L5-6 caudal to the left kidney.
    • Nearer the midline than the right ovary.
  • Both ovaries are embedded in fat.


  • Oviduct is convoluted and winds around the ovary in 10-12 loops.



  • Vaginal opening lies caudal to clitoral glands and is closed by a membrane until puberty.
    • Clitoral (Preputial) Glands: Lie in subcutaneous fat near the clitoris and open into a preputial fold.
      • Sebacious glands that secrete a pheromone used for scent marking.

Attachments and Blood Supply

  • Anastamoses between the ovarian and uterine artery occur in the uterine mesentery.
  • Mesovarium and mesometrium contain large volumes of fat, which surround the kidneys, abdominal wall and intestinal loops.

Oestrous Cyclicity

  • Non-seasonal polyoestrus
  • LH surge (responsible for ovulation) is strongly linked to circadian rhythm and usually occurs in the late afternoon.
  • Oestrus cycle 4-5 days.
  • Duration of oestrus is ~14 hours.

Gestation and Offspring


  • Gestation length is 20-22 days.
  • Placenta is haemochorial.


  • Litter size 6-16
  • Altricial young
    • Eyes open at 12-14 days.
  • Earliest weaning age 21 days.
  • Care not to stress mother or she may cannibalise the young.

Mammary Gland and Lactation

  • The rat has 6 pairs of mammary glands.
  • Thoracic and inguinal glands act as two discrete complexes, separated by a space just behind the ribs.
    • During lactation, the thoracic glands expand rostrally as far as the parotid and mandibular glands.
      • Cranially and medially over the upper forelimb and along the lateral thoracic wall.
    • Inguinal gland covers the lateral abdominal wall back to the stifle and anal region.
  • At the base of each teat the transition zone between hairless and hair has large sebacious glands.

Cervical gland

  • Rudimentary

Thoracic gland

  • Diffuse.
  • Contains 3 nipples
  • Surrounds the base of the forelimb.

Abdominal gland

  • Only marginally developed.

Inguinal gland

  • Surrounds the base of the hindlimb.
  • Contains 3 nipples.