Artificial insemination

Reproductive organs

Male (bull): testes produce sperm and the hormone testosterone; the scrotum keeps testes a few degrees cooler than the body, which is needed for sperm formation; the epididymis stores and matures sperm; the vas deferens carries them; accessory glands (seminal vesicles, prostate, bulbourethral or Cowper's glands) add fluid; the penis delivers semen.

Female (cow): ovaries produce eggs (ova) and the hormones oestrogen and progesterone; the oviduct (fallopian tube) is where fertilisation takes place; the uterus holds the developing foetus; the cervix is a muscular neck that closes the uterus; then the vagina and vulva. The oestrous (heat) cycle of the cow is about 21 days; heat lasts roughly 18 hours. Signs: bellowing, restlessness, clear mucus discharge, swollen vulva, mounting others and standing to be mounted (the surest sign).

Artificial insemination (AI)

AI is the collection of semen from a male and its deposition into the female reproductive tract with instruments, without natural mating. Spallanzani first did it successfully in a dog in 1780.

• Collection: mainly with an artificial vagina; an electro-ejaculator is used for bulls that cannot mount.
• Evaluation: volume, colour, sperm concentration and motility are checked.
• Dilution: semen is extended with diluters such as egg yolk–citrate or egg yolk–tris, which supply energy, protect against cold shock and keep pH stable; antibiotics are added.
• Preservation: frozen semen in straws stored in liquid nitrogen at −196 °C can be kept for years.
• Insemination: in cattle by the recto-vaginal (recto-cervical) method, depositing semen in the uterine body just beyond the cervix. Best time is mid to late heat: by the AM–PM rule, a cow seen in heat in the morning is inseminated in the evening, and one seen in the evening is inseminated next morning.

Role in cattle improvement: one ejaculate from a superior bull can serve many cows; semen can be sent far away and used after the bull's death; it prevents the spread of venereal diseases; allows progeny testing and crossbreeding with exotic breeds; saves the cost of keeping bulls. Limits: needs trained staff, proper heat detection and liquid nitrogen supply.

Key points

• Fertilisation site: oviduct; heat cycle ≈ 21 days.
• Collection: artificial vagina; storage: liquid N₂ at −196 °C.
• AM–PM rule for timing.
• Recto-vaginal method in cattle.

Exam tips

Questions test organ functions, storage temperature, timing of AI and advantages.

Common mistakes

• Saying fertilisation occurs in the uterus; it happens in the oviduct.
• Inseminating at the very start of heat; mid to late heat is best.