Rat Reproduction - Anatomy & Physiology

Male

Penis

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

Testes

• 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.

Female

Reproductive tract

Ovary

• 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

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

Uterus

• Duplex Uterus
  • Two cervices
  • Uterine horns remain separate until uniting in a single vagina.

Vagina

• 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

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

Litter

• 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.