Lecture 7

What hormone is responsible for signs of oestrus?

Oestrogen

What is the most reliable sign of sexual receptivity in animals?

Standing heat

What is a common behavioral sign of a cow in heat?

Cow riding other cows

Which animal cannot use artificial insemination?

Thoroughbreds

What is the detection method used for canines in heat?

Vaginal speculum exam, exfoliative cytology, or serum progesterone

What is the prerequisite for synchronisation of oestrus

Active ovaries 

What are the two basic mechanisms for manipulating oestrus

Inducing luteolysis (shortening luteal phase) or prolonging the luteal phase

How would you induce luteolysis?

Use of PGF2 alpha injection on CLs that are older than 5 days to shorten the luteal phase

How would you prolong the luteal phase ? 

Progesterone via the controlled intravaginal drug release (CIDR) or progesterone impregnated intravaginal device (PRID) in ruminants

Horses can use an oral or injectable progesterone

What are the two methods to induce ovulation

1. Human chorionic gonadotropin or gonadotropin-releasing hormone (GnRH) analogs.

When is human chorionic gonadotropin given in horses vs GnRH analogs?

When the follicle is at least 35mm for HCG and there is oedema present, and when the follicle is 30mm for GnRH

When does ovulation occur for the two different ovulation induction methods

HCG → 36-42 hours

GnRH → 42-48 hours

What is the role of GnRH analogue in ovulation induction for equines?

It promotes LH FSH production which increases follicle size and promotes ovulation

How can the cycles of seasonal breeders be manipulated?

Through artificial light exposure and melatonin implants (in sheep)

How is AI typically performed in cows?

By depositing semen into the uterine horn.

What is a major difference in the AI process for dogs compared to other animals?

Fresh semen is inseminated via vagina; for uterus access = transcervically or surgically.

Explain the advantages and disadvantages and use of fresh and frozen semen in domestic species

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 lifespan after thawed and needs to be done really close to ovulation