Birth to puberty

when does testes descent take place in:

1. bull

2. stallion

3. dog

1. 3.4-4 mo during gestation

2. late pregnancy or a few days after birth

3. up to 8 days after birth

in which species do the testes remain within the abdomen?

• elephants

• whales

what happens during the transabdominal phase of the testicular descent?

• testicle is pulled by the gubernaculum growing through the deep inguinal canal towards the scrotum

• causes a layer of peritoneum to encapsulate the testes → visceral vaginal layer which further pulls the testes down

what is the inguinal-scrotal phase of testicular descent

• gubernaculum begins to regress creating the parietal vaginal layer and forming the vaginal cavitywh

what is the fluid in the vaginal cavity?

• peritoneal fluid

define puberty

• a developmental process where endocine + morphological changes transform the animal into an individual capable of reproducing

what determines pattern of GnRH secretion?

• the differeces in development of the hypothalamus

what is a requirement of puberty?

• GnRH secretion at the appropriate frequency and quantity to stimulate gonadotrophin release from the anterior pituitary

compare the male and female hypothalamus

• both have a tonic centre

• only females hav e surge centre

compare the LH secretion in males and females post-puberty

• males have a consistend episodic LH pattern post-puberty

  • females have a surge of LH release prior to ovulation in addition to a consistent episodic pattern of LH

why don’t males develop a surge centre/

• testosterone passes through BBB in development and is turned into oestradiol by aromatose which inhibits surge centre development

what limits puberty onset in females?

• the hypothalamus - GnRH levels are too low to stimulate FSH/LH release

why is the female LH only produced by the tonic centre during pre-puberty?

• below the minimum threshold of oestradiol needed to stimulate GnRH in the surge centre

pre-puberty how do low oestradiol levels affect:

1. surge centre

2. tonic centre

1. no effect

2. inhibition

during the transition to puberty how do the oestradiol levels affect the tonic centre?

• inhibition switches to being stimulatory (mechanism unkown)

• this causes more GnRH secretion → increased FSH/LH → increased oestradiol → +ve feedback

once oestradiol has a positive effect on the tonic centre, what happens to the surge centre?

• increasing oestradiol levels cause surge centre to release large GnRH release (a surge) → ovulation

how does the method of oestradiol on the tonic centre in females and males compare?

• it doesn’t - same principle of oestradiol not inhibiting → greater GnRH etc

what are 4 indices of male puberty onset

1. behavioural

2. first ejaculation

3. age when first sperm appears in ejaculate

4. age when ejaculate contains a certain number of sperm

what impacts female puberty:

1. fat

2. body maturation

3. season animal bron in

4. photoperiod at puberty

5. presence/absence of opposite sex

6. density of same sex groups.

what are the 3 types of pre-synaptic neurones in females

1. glucose sensitive

2. fatty acid sensitive

3. leptin sensitive

what are the pre-synaptic neurones in females highly sensitive to?

• metabolic status

what do leptin, fatty acids and glucose promote activity in in the female?

• kisspeptin neurones

why is knowing about pre-synaptic neurones in females important?

• demonstrates how nutrition can impact puberty but influencing the signalling between neurones

what signalling pathway is a prerequisite for the onset of puberty

• kisspeptin signalling pathway

what receptor does kisspeptin express?

• oestrogen

why are kisspeptin neurones relevant?

• have oestrogen receptors therefore must be involved in change of oestradiol concentrations with the HPG axis during puberty.

• act on the surge centre in females

how can we affect puberty with nutrition?

1. high plane → early puberty

2. low plane → delays puberty

how does hybrid vigour affect puberty?

• decreases age of puberty

what particularly in ewes affects puberty?

• photoperiod

how can we influence puberty with hormones/

• GnRH induction of early puberty in gilts

• eCG can be used for some domestic animals

how does puberty compare in spring + autumn born lambs?

• spring - earlier and more spread out ages of onset

• autumn - later and within a shorter time-period