Oestrus and ovulation manipulation Flashcards
What is the HPO axis?
Hypothalamus produces GnRH which acts on
Anterior pituitary which produce LH and FSH
Which act on ovary to produce progesterone, inhibin and estradiol
What does oestradiol increase in the endometrium?
Oxytocin receptors
Where is oxytocin produced? What does it cause the release of?
Corps luteum
Release of PGF2a from endometrium
Where is progesterone produced? Which hormones does it suppress and what does this prevent?
Corpus luteum
FSH and LH - prevents ovulation
What happens to follicles as progesterone concentrations fall?
Follicles develop and secrete oestradiol
What does the dominant follicle secrete? What is the result of this?
Inhibin
Suppresses FSH - FSH surge not as strong as LH one
What are the 5 phases of the oestrus cycle?
Pro-oestrus Oestrus Metoestrus Dioestrus Anoestrus
When does pro-oestrus take place? What does it cause?
Immediately before oestrus
Increase in activity - follicular growth, regression of CL from previous cycle
Describe pro-oestrus vaginal mucus
Hyperaemic
Describe the histology of a pro-oestrus smear
Cornified cells
Large cytoplasm
What is oestrus?
Period where female will accept male for copulation
In which phase of the oestrus cycle does ovulation occur? Which species is the exception?
Oestrus
Cows - ovulate 12 hrs after end of oestrus
What is the phase after oestrus? What happens?
Metoestrus
Oestrogen and progesterone levels low - reduced secretions from uterine, cervical and vaginal glands
What is the phase after met oestrus and what happens?
Dioestrus
Corpus luteum are functional and secrete large amounts of progesterone
Which is the longest phase of the oestrus cycle?
Dioestrus
What happens during anoestrus?
Quiescence Minimal follicle development CL regressed and non-functional Lack of FSH and LH Lack of ovarian response
Describe the cytology of a smear taken during anoestrus?
Parabasal cells
Rounded cytoplasm with round nucleus
Describe the cytology of a smear taken during oestrus
Complete cornification
Cells with no nucleus
How many waves are usually in a cycle? Which species is the exception?
3 wave cycle
Cows have 2 wave cycle
What is meant by a wave in a cycle?
Follicle development before luteolysis
How long is oestrus behaviour in cows?
9-14 hours
Heat detection rate is low in cattle (60-80%) and there is a low heat detection accuracy. Why is this?
Unaware of signs
Cows occupied
After midnight
Less than half animals show behaviour of standing to be mounted
How can you detect when a cow is in oestrus?
Riding marks on hide Bulling string - thick mucus form vulva Tail paint Mount indicator Pedometer
What should be observed when examining follicles?
Shape Size Softness Wall thickness Oedema
How much do follicles grow roughly a day (LA)?
3-5mm
What size and shape of a follicle indicate ovulation?
> 35mm diameter
Tear drop shape
Thickened wall
How long is the mare cycle? How long is oestrus? When does ovulation occur?
21 days
Oestrus for 7 days
Ovulation 24-48hrs before oestrus ends
Why might oestrus be manipulated?
Synchronisation
Easier oestrus detection
Enable AI and ET
Trigger post-partum resumption
With oestrus manipulation, what are we aiming to control?
Corpus luteum influence and follicular waves
What hormone should be given to shorten the luteal phase?
PGF2a
What hormone should be given to extend the luteal phase?
Progesterone
For fixed time AI in heifers, what hormone should be given twice? (11 days apart)
PGF2a
How can exogenous progesterone be given to sheep/cattle?
Intra-vaginal progesterone device/progesterone releasing uterine device (PRID)
Progesterone sponge
What hormone might be given to cattle with insertion of an intra-vaginal progesterone device?
GnRH
How long do sheep have a progesterone sponge in for?
9-19 days
What are causes of anoestrus?
Pregnancy Lactation Stress Season Negative energy balance Pathology
What is the suckling effect in beef cows?
More suckling –> low frequency of LH pulses
Less suckling –> dramatic increase in LH pulses
How does the insertion and removal of a progesterone releasing intra uterine device alter GnRH?
Inserting PRID - GnRH suppression
Removing PRID - GnRH surge
How can puberty be induced in sows?
PMSG
hCG
How can oestrus be synced in sows?
Progesterone
For AI in a mare, how long is the lifespan of semen if fresh, chilled or frozen? How long is the viable life of an ovum in comparison?
Fresh - 72 hrs
Chilled - 24hrs
Frozen - 12 hrs
Ovum life shorter
