Puberty and seasonality

Question 1

Development of what is important for puberty to happen?

Answer 1

Hypothalamus

Question 2

What are the differences between the male and female hypothalamus?

Answer 2

The female hypothalamus has a surge centre and a tonic centre. Post puberty there is a LH surge.

The male has no surge centre and LH is secreted in a relatively consistent pattern. (LH binds to leydig cells to make testosterone)

Question 3

How is the female brain feminised and the male brain masculinised?

Answer 3

Binding of E2 to aFP prevents e2 passing through blood brain barrier in female so surge centre can develop in the female.

E2 can cross BBB in male and prevents development of surge centre.

Question 4

At puberty what happens to the neurons?

Answer 4

Presynaptic neurons synapse onto Gnrh neruons at puberty there is a change in activity of the presynaptic neurons.

Question 5

In men what happens to the frequency of GnRH after puberty?

Answer 5

There are no surges in the male but there is an increase in basal frequency.

Question 6

In women what happens to the frequency of GnRH after puberty?

Answer 6

The surge centre develops and controls the pre-ovulatory surge of GnRH that causes the pre-ovulatory surge of LH.

Question 7

How does nutritional status effect puberty in the female?

Answer 7

GnRH neurones are sensitive to metabolic status
The three main types are pre-synaptic neurones
— Glucose sensitive neurones
— Fatty acid sensitive neurones
— Leptin sensitive neurones
Leptin (produced by adipose tissue), fatty acids &
glucose thought to promote activity in “kisspeptin
neu rones” these neurons synapse on GnRH
neurons.
Therefore good nutrition means earlier puberty.

Question 8

What are some seasonal polyestrus long day breeders?

Answer 8

The mare

Question 9

What are some seasonal polyestrus short day breeders?

Answer 9

Ewe, doe, elk, nanny

Question 10

What are some examples of mono-oestrus breeders?

Answer 10

Dog, wolf, fox, bear

Question 11

What are some examples of polyoestrus breeders?

Answer 11

Cow, pig, rodent.

Question 12

With regards to seasonal breeders what triggers return to cyclicity?

Answer 12

Long day breeders
— lengthening daylight hours
— increasing plane of nutrition
Short day breeders
— shortening daylight hours
Melatonin which is synthesised by the pineal gland

Question 13

What does melatonin do to long day breeders?

Answer 13

Represses reproduction in the short months. The delcining melatonin (darkness) in long days triggers GnRH release.

Question 14

What does melatonin do to short day breeders?

Answer 14

Stimulates reproduction. The increase in melatonin (darkness) in the short days triggers GnRH release.

Question 15

What are the controlling factors of cyclicity?

Answer 15

Photoperiod, melatonin, temperature, nutrition, lactation, pregnancy.

Question 16

What does LH do and where is it produced?

Answer 16

LH: The surge induces ovulation, is a hormone produced by gonadotropic cells in the anterior pituitary gland. In females, an acute rise of LH triggers ovulation and development of the corpus luteum. In males, where LH had also been called
interstitial cell—stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistic-ally with FSH.

Question 17

What does FSH do and where is it produced?

Answer 17

• FSH: stimulates follicular growth, particularly small antral follicles, it also stimulates the recruitment wave of follicles thereby increases estradiol E2.

FSH: anterior pituitary

Question 18

What are the characteristics of short day breeders?

Answer 18

Short day breeders (e.g. sheep, goat)
— Increasing melatonin (shortening daylight hours)
— Increased synthesis
— Increased FSH, then LH

Question 19

What are the characteristics of long day breeders?

Answer 19

Long day breeders (e.g. horse, fox, queen)
— Decreasing melatonin (lengthening daylight hours)
— In conjunction with increasing plane of nutrition
— Increased GnRH synthesis

Question 20

Do uterine involution and resumption of ovarian activity happen at same time?

Answer 20

No. It varies. Some are influence by weaning even if uterus has involuted.
In the mare the uterus involutes in 14 days and returns to ovarian cyclicity in 5-12 days however in te Ewe and bitch there are atleast 30-40 days between involution and return to cyclicity.

Question 21

What can cause extended anoestrus post partum?

Answer 21

Lactation/suckling
Prolactin (particularly in sows, women)
— Prevents pregnancy before weaning
. Mammary stimulation/suckling suppresses GnRH
. Offspring influences e.g. visual, olfactory, auditory
- eg beef vs dairy cows
. Weaning promotes ß/LH secretion

Question 22

What can hasten cycle resumption?

Answer 22

Early weaning.

Question 23

What are common influences on delayed return to cyclicity?

Answer 23

Suckling
• prolactin/ presence of offspring
• ATCH/Corticosteroids

Peri-parturient abnormalities
• Retained fetal membranes
• Endometritis

Milk yield/Nutrition
• Body condition score
• Negative energy balance t

Parity
. Especially in primiparous (bearing
of first child)