Assisted Reproductive Technologies in Livestock

Definition and Purpose of Assisted Reproductive Technologies (ARTs)

  • Definition: ARTs describe treatments and procedures involving the manipulation of reproductive cycles, gametes, or embryos.

  • Objectives:

    • Improve reproductive efficiency and profitability.

    • Accelerate genetic progress and enable global trade in genetics.

    • Overcome management constraints and control disease transmission.

Evolution of ARTs

  • First Generation (late 1800s – early 1900s): Foundational manipulation including Artificial Insemination (AI) and basic semen cryopreservation.

  • Second Generation (1930s – 1980s): Female cycle control via oestrus synchronization, superovulation, and Embryo Transfer (ET).

  • Third Generation (1960s – 1990s): In vitro manipulation, including IVF, In Vitro Embryo Production (IVP), and embryo cryopreservation.

  • Fourth Generation (1980s+): Genetic-level precision breeding, including cloning, gene editing, and commercial sexed semen.

Semen Collection and Handling

  • Artificial Vagina (AV) Method: Most common method; temperature and pressure are adjusted to suit the male.

  • Electroejaculation (EE) Method: Used for young or untrained males; involves transrectal massage and electrical pulses (8−16V8-16V); considered stressful and painful.

  • Transrectal Massage (TRM): Less stressful than EE but yields lower sperm quality than AV.

  • Storage Types:

    • Fresh: Inseminated within hours; high fertility.

    • Chilled: Diluted and cooled (4−5 ∘C4-5\,^{\circ}C); stored up to 55 days.

    • Frozen: Extended with cryoprotectants (e.g., glycerol) and stored in liquid N2N_2 at −196 ∘C-196\,^{\circ}C.

  • Cryopreservation Success: High in bulls and rams (approx. 50%50\% post-thaw motility); unsuccessful in boars.

Artificial Insemination (AI) Strategy

  • Species-Specific Use:

    • Cattle: Frozen semen is the industry standard.

    • Pigs: Fresh or chilled semen is common; frozen is rare due to poor thaw survival.

    • Sheep: Frozen semen is used specifically with laparoscopic AI.

  • Deposition Sites:

    • Cows: Transcervical (TC) intrauterine.

    • Ewes: Vaginal/cervical (fresh) or Laparoscopic (frozen).

    • Sows: Cervical or deep intrauterine.

  • Timing: Success depends on insemination close to ovulation. Sperm lifespan is 24−3024-30 hours; oocyte lifespan is 6−126-12 hours.

Oestrus Synchronization and Control

  • Rationale: Enables Fixed-Time Artificial Insemination (FTAI), shortens birthing periods, and eliminates the need for natural heat detection.

  • Hormonal Methods:

    • Luteolysis (CL Regression): Prostaglandins (PGF2αPGF_2\alpha) such as Lutalyse, Estrumate, or Cyclix; Progestins such as CIDR, PRID, or Regumate.

    • Follicle Control: GnRH (Receptal) or Gonadotrophins (PG600).

  • Other Methods: Socio-sexual signals (teaser males), nutrition (flushing), and environmental lighting.

Multiple Ovulation and Embryo Transfer (MOET)

  • Process:

    1. Superovulation: Using FSHFSH to increase egg release.

    2. Insemination: Typically FTAI.

    3. Flushing: Non-surgical recovery of embryos approx. 77 days post-insemination.

    4. Grading: Evaluating embryos for symmetry and cellular integrity.

    5. Transfer: Implanting into recipients synchronized to the same cycle stage as the donor.

  • Conception Rates: 60−70%60-70\% for fresh embryos; 50−60%50-60\% for frozen embryos.