Puberty

Question 1

Define puberty

Answer 1

Puberty: A developmental process in which endocrine and morphologic changes transform the animal into an individual capable of reproducing.

Question 2

There must be sufficient secretion of what to allow puberty too unfold?

Answer 2

For puberty to occur there must be secretion of GnRH at the appropriate frequency and quantity to stimulate gonadotrophin release by the anterior pituitary.
Development of the hypothalamus is important for this.

Question 3

What is the difference between the male and the female hypothalamus?

Answer 3

Females have a surge centre & tonic centre within the hypothalamus and after puberty females will have pre ovulatory LH surges every 20 days or so.
Males have no surge centre so post puberty LH follows a relatively consistant episoidic pattern.

Question 4

In females what is the trigger for puberty?

Answer 4

Pre puberty there is very little release of GnRH/LH and FSH.
As we approach puberty the negative feedback of low oestradiol on the tonic centre is reduced and the levels of GnRH, FSH and LH increase which then acts to increase oestradiol.
So the trigger for puberty is the decrease in the negative feedback of the tonic centre.

Question 5

What is the trigger for puberty in males?

Answer 5

pre- puberty testosterone has a negative feedback and supresses the GnRH neurones, as the male approaches puberty the neurones become less sensitive to this negative feedback and GnRH levels rise which causes LH and FSH levels to rise with it.

Question 6

Why does the amount of fat and body size affect puberty onset?

Answer 6

GnRH neurones sensitive to metabolic status

Question 7

What other factors could influence the onset of puberty?

Answer 7

Season when animal born eg sheep
Photoperiod that animal experiences at puberty eg. sheep (short day length trigger)
Presence and absence of opposite sex just prior to puberty eg. swine and cattle (pheromones, visual)
Density of same sex groups eg in Swine

Question 8

When do cows start puberty?

Answer 8

11 months

Question 9

When do dogs start puberty?

Answer 9

Male - 9 months

Female - 12 months

Question 10

When do horses start puberty?

Answer 10

Males - 14 months

Females - 18 months

Question 11

When do cats start puberty?

Answer 11

Males - 9 months

Females - 8 months

Question 12

When do sheep start puberty?

Answer 12

7 months

Question 13

When do pigs start puberty?

Answer 13

Male - 7 months

Female - 6 months

Question 14

What are the seasonal effects on the male?

Answer 14

Low testosterone production
Reduced or cessation of sperm production
Reduced sperm motility
Testes involute
Behavioural factors – willingness to breed

Question 15

What initiates the HPG axis before puberty and the breeding season?

Answer 15

GnRH