Oestrus and ovulation manipulation Flashcards
Which hormone is produced by the hypothalamus in the HPO axis?
GnRH
What occurs following the release of GnRH?
Acts on the pituitary gland which then releases FHS and LH which act on the ovary
Where is PGF2a produced?
Endometrium
A sharp spike in which hormone causes ovulation?
LH
Which hormone is present at high levels during diestus?
Progesterone
What change in hormone levels occurs as the CL regresses?
- Progesterone levels decrease
- Oestrogen, LH and FSH levels increase
A rise in the level of which hormone causes the behavioural signs seen at oestrus?
Oestrogen
In a cow, describe the 1st follicular wave
- From the follicular pool, follicles are recruited
- They enter a selection/growth phase
- One (possibly 2) will become dominant
- It secretes inhibin to stop the others growing further
- As the CL is still present, progesterone is still produced so the follicle cannot ovulate
- Atresia occurs
Which 2 factors are important when it comes to oestrus detection?
- Heat detection rate
- Heat detection accuracy
What is the single absolute sign that a cow is in oestrus?
Stands to be mounted
In a cow why can oestrus easily be missed?
9-14 hour window but only mount for a few seconds around 10 times in this period
What are some physical signs of oestrus?
- Riding marks
- Bulling string
- Swelling of vulva and discharge
- Restlessness
What are some oestrus detection aids?
- tail paint/chalk
- mounting indicator
- activity monitors
In a mare, what is the daily growth of a follicle and at what size do they ovulate?
Daily growth = 3-5mm
Ovulate > 35mm
Why is observation of follicles particularly important in the mare?
Ovulate before the end of oestrus so need to be able to predict when it will occur
How does a follicles appearance change as ovulation approaches?
- Teardrop shape <24h of ovulation
- Become softer <6-12h of ovulation
- Follicle wall thickens <24h prior to ovulation
In vaginal cytology of the bitch, how does the number of parabasal cells and cornified cells change?
- In pro-oestrus the number of cornified cells increase by 10% each day
- During oestrus 100% of the cells are cornified
- Di-oestrus day 1: abrupt change to 50% non-cornified
What are some reasons that we would want to manipulate oestrus?
- Poor oestrus detection
- Syncronisation
- AI and Embryo transfer
Which hormones are used to:
- prolong the luteal phase
- shorten the luteal phase
1 = progesterone 2 = PGF2a
Which hormone is used in follicular recruitment and growth?
GnRH
In heifers which process is used for syncronisation?
- Double dose of PGF2a, 11 days apart
- Double AI 72 and 96 hours following last dose
How does a double dosage of PGF2a cause syncronisation?
1st dose: - Causes luteolysis - New follicle produced - Ovulation occurs - New CL forms 2nd dose: - All have a CL -> luteolysis - New follicle - Ovulation
How is exogenous progesterone used in cycling?
- Intra-vaginal progestrone device
- Puts everything on hold
- As progesterone device is removed it removes negative feedback on hypothalamus
- GnRH is released and ovulation can occur
What are some causes of anoestrus?
Nutrition Lactation Energy deficiency Stress Pregnancy Illness/disease
How can anoestrus be managed?
- use a progesterone device to suppress GnRH
- after 7 days remove the device causing a surge in GnrH
