Oestrus and ovulation manipulation

Question 1

Which hormone is produced by the hypothalamus in the HPO axis?

Answer 1

GnRH

Question 2

What occurs following the release of GnRH?

Answer 2

Acts on the pituitary gland which then releases FHS and LH which act on the ovary

Question 3

Where is PGF2a produced?

Answer 3

Endometrium

Question 4

A sharp spike in which hormone causes ovulation?

Answer 4

LH

Question 5

Which hormone is present at high levels during diestus?

Answer 5

Progesterone

Question 6

What change in hormone levels occurs as the CL regresses?

Answer 6

• Progesterone levels decrease

- Oestrogen, LH and FSH levels increase

Question 7

A rise in the level of which hormone causes the behavioural signs seen at oestrus?

Answer 7

Oestrogen

Question 8

In a cow, describe the 1st follicular wave

Answer 8

• 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

Question 9

Which 2 factors are important when it comes to oestrus detection?

Answer 9

• Heat detection rate

- Heat detection accuracy

Question 10

What is the single absolute sign that a cow is in oestrus?

Answer 10

Stands to be mounted

Question 11

In a cow why can oestrus easily be missed?

Answer 11

9-14 hour window but only mount for a few seconds around 10 times in this period

Question 12

What are some physical signs of oestrus?

Answer 12

• Riding marks
• Bulling string
• Swelling of vulva and discharge
• Restlessness

Question 13

What are some oestrus detection aids?

Answer 13

• tail paint/chalk
• mounting indicator
• activity monitors

Question 14

In a mare, what is the daily growth of a follicle and at what size do they ovulate?

Answer 14

Daily growth = 3-5mm

Ovulate > 35mm

Question 15

Why is observation of follicles particularly important in the mare?

Answer 15

Ovulate before the end of oestrus so need to be able to predict when it will occur

Question 16

How does a follicles appearance change as ovulation approaches?

Answer 16

• Teardrop shape <24h of ovulation
• Become softer <6-12h of ovulation
• Follicle wall thickens <24h prior to ovulation

Question 17

In vaginal cytology of the bitch, how does the number of parabasal cells and cornified cells change?

Answer 17

• 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

Question 18

What are some reasons that we would want to manipulate oestrus?

Answer 18

• Poor oestrus detection
• Syncronisation
• AI and Embryo transfer

Question 19

Which hormones are used to:

1. prolong the luteal phase
2. shorten the luteal phase

Answer 19

1 = progesterone 
2 = PGF2a

Question 20

Which hormone is used in follicular recruitment and growth?

Answer 20

GnRH

Question 21

In heifers which process is used for syncronisation?

Answer 21

• Double dose of PGF2a, 11 days apart

- Double AI 72 and 96 hours following last dose

Question 22

How does a double dosage of PGF2a cause syncronisation?

Answer 22

1st dose:
- Causes luteolysis
- New follicle produced
- Ovulation occurs
- New CL forms
2nd dose:
- All have a CL -> luteolysis
- New follicle
- Ovulation

Question 23

How is exogenous progesterone used in cycling?

Answer 23

• 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

Question 24

What are some causes of anoestrus?

Answer 24

Nutrition
Lactation
Energy deficiency 
Stress
Pregnancy
Illness/disease

Question 25

How can anoestrus be managed?

Answer 25

• use a progesterone device to suppress GnRH

- after 7 days remove the device causing a surge in GnrH