Season and its manipulation

Question 1

What factors control seasonality in oestrus?

Answer 1

Photoperiod
Melatonin - secreted when dark, direct influence on HPO axis
Temp
Nutrition - spring and autumn grass

Question 2

What causes the resumption of cyclicity after seasonal anoestrus in short day breeders?

Answer 2

Shorter daylight hours => increased melatonin from pineal gland => increased GnRH synthesis => increased FSH and LH

Question 3

What causes the resumption of cyclicity after seasonal anoestrus in long day breeders?

Answer 3

lengthening daylight hours => Decreasing melatonin from pineal gland
Increasing plan of nutrition
Increased GnRH synthesis

Question 4

Give examples of short and long day breeders

Answer 4

Short day e.g., sheep => summer anoestrus
Long day e.g., horse => winter anoestrus

Question 5

Describe the process of the transition period in the mare

Answer 5

Increased GnRH => increased FSH but not LH
Initiation of antral folliculogenesis (suboptimal follicles)
Irregular oestrus
Increased steroidogenic competence
Increased LH
Ovulation
Normal cycling

Question 6

How can seasonality be manipulated in seasonal polyestrus animals?

Answer 6

change of photoperiod:
- artificial e.g., provide lights
- physical - transport them from northern to southern hemispheres

Hormonal manipulation:
- melatonin for a sustained period in long day periods to sheeps
- GnRH
- equine chorionic gonadotrophin (ECG) - FSH/LH activity, direct stimulation of ovary
- progesterone (in combination with ECG)