manipulation of seasonality

Question 1

non-seasonal polyoestrus will breed when

Answer 1

• anytime throughout the year
• have regular intervals of oestrus

Question 2

What type of breeder are horse classed as

Answer 2

seasonal polyoestrus, long day breeders (anoestrus in the summer, want to foal in spring)

Question 3

It is mid-august and you wish to induce a group of ewes into oestrus earlier in the season. How would this typically be managed?

Answer 3

treatment with progesterone and ECG

Question 4

It is mid-December and you wish to induce a mare into oestrus earlier in the season. How would this typically be managed?

Answer 4

put mare under artificial light

Question 5

What is the effect of melatonin on the HPO axis in cows

Answer 5

it has no effect as cows are not seasonal breeders

Question 6

When the mare resumes ovarian activity after seasonal anoestrus her oestrus behaviour is typically

Answer 6

irregular and erratic oestrus patterns

Question 7

what factors influence seasonality

Answer 7

• photoperiod (minor at equator)
• melatonin (princioak factor)
• temp
• nutrition

Question 8

how do short day breeders return to cyclicity after seasonal anoestrus

Answer 8

• increasing melatonin
• acts on hypothalamus to release GnRH
• therefore increased FSH then LH

Question 9

how do long day breeders return to cyclicity after seasonal anoestrus

Answer 9

• decreasing melatonin from pineal gland due to lengthening of daylight hours
• increasing plane of nutrition
• increased GnRH synthesis

Question 10

discuss significance of the the period of transition between seasonal anoestrus and cyclicity in the mare

Answer 10

• durin winter anoestrus, ovaries are shrunken and not functional (no follicular or luteal activity)
• transition takes 50-60 days
• during this period they will have irregular and erratic eostrus behaviour
• transition follicles form, but they are non-functional. regress

Question 11

how do you commonly manipulate seasonality in the mare

Answer 11

artificially change photoperiod

Question 12

discuss options for hormonally manipulating seasonality

Answer 12

• in the sheep and goat –> give melatonin (just after long day period for sustained period of time)
• GnRH (but not in deep anoestrus)
• equine chorionic gonadotrophin (directly stimulates ovary)
• progesterone (in combo with ECG) given just before transition period in horse, mimics luteal phase, then when withdrawn, mimics luteolysis