Lecture 7

Oestrus Detection

Oestrogen is responsible for signs of oestrus

Standing heat is the most reliable sign for sexual receptivity

There are exceptions !

Cow riding other cows

Teasing the mare with a stallion

Remember thoroughbreds cannot use AI

Canines can be in standing heat anywhere from pro-oestrus till the end of oestrus

Detection is via:

• Vaginal speculum exam → look for dry vaginal folds

• Exfoliative cytology

  

• Serum progesterone

Manipulation of the Cycle

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Prerequisite for synchronisation of oestrus is active ovaries

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Two basic mechanisms:

1. Inducing luteolysis

   Use PGF2 alpha → one off injection

   Prostaglandin only works on corpus lutea >5days

   Single dose is strong in inducing abortion

   Synchronisation is not very tight

   • Can use in ruminants 11 days apart

   • Can use in horses 12-14 days apart

   

2. Prolonging luteal phase

   Use progesterone

   In ruminants can use controlled intravaginal drug release (CIDR) or progesterone i mpregnated intravaginal device (PRID)

   In horses can use via oral or injection

   In pigs can use oral

Ovulation induction

Assumed to be as fertile as a spontaneous one

We use:

• Human chorionic gonadotropin → has LH like function → given IV → results in Ab production but these are not relevant

  • Given in horses when follicle is at least 35mm

    • 85% ovulate in 36-42 hours

    • Needs to have oedema present which is based on follicle size

• GnRH analogue

  • Equine uses deslorelin → given when follicle is smaller (30mm)

    • Ovuation occurs between 42-48 hours

    • Give at smaller follicle size due to mechanism of action direct on pituitary (c.f above) so promotes FSH production which increases follicle size as well

Seasonal Breeders

Can manipulate artificial light exposure to manipulate cycles of seasonal breeders (so either more or less light)

Can also use melatonin implants to alter the pathway related ton light exposure (lec 6)

• For sheep only

Artificial Insemination

1. Semen collected

2. Placed in semen extender to protect against damage

   • Can be used in multiple females → split semen across animals

   • Increases longevity when not being use immediately

   Components:

   • Buffer

   • Energy source

   • Antimicrobial

   • May have cryoprotectants if being frozen

3. AI of the female with the sperm

   • Note that in the cow they usually deposit the semen into the uterine horn because you need less sperm # to do so compared to depositing into the vagina and letting the sperm swim

     

     If sperm is deposited in uterus body → could see backflow or intracervical insemination (right side image)

   • Mare AI

     • Also deposited into the uterus

       • Low doses = closer to horns → for valuable semen usually

   

   • Sow AI

     

   • Dog AI

     • Fresh is inseminated via vagina

     • To get into the uterus you need go either transcervically or surgery

     

Fresh vs Frozen

Fresh extended semen has a limited life span of 1-2 days or up to a week in pigs. In horses, after semen is deposited then the sperm is still fertile for another day or two

Frozen semen has a longer lifespan but a has a short lifespand after thawed and needs to be done really close to ovulation