Puberty and seasonality Flashcards
Compare the hypothalamus of the male and female
- Female has surge and tonic centre
- Male has no surge centre
Describe the post-puberty LH release in males and females
- LH surges in females every ~20 days, lower amplitude higher frequency pulses in between peaks
- In male have consistent episodic pattern
What stimulates the release of FSH and LH from the pituitary?
GnRH from the hypothalamus
What is the benefit of seasonal breeding?
Ensures offspring are born when there is optimum survival
Describe anoestrus in the female in the non-breeding season
- No oestrus cycle
- Ovaries inactive
- Due to decreasing GnRH, LH and FSH
What stimulates the termination of anoestrus in long day breeders?
- Lenghtening daylight hours
- Increasing plane of nutrition
What stimulates the termination of anoestrus in short day breeders?
Shortened daylight hours
What are the seasonal effects on the male?
- Low testosterone production
- Reduced or cessation of sperm production
- Reduced sperm motility
- Testes involute
- Willingness to breed may change
Define puberty
The developmental process to transform the individaul into one capable of reproducing
What types of changes take place during puberty?
- Endocrine
- Morphological
What happens to the hypothalamus at puberty?
- Change in activity of higher pre-synaptic neuones
- Stimules GnRH neurones
- Leads to GnRH secretion
- Which in turn stimulates the gonadotrophins initiation gametogenesis, steroidogenesis and reproductive tissue development
Describe the hypothalamus of the female following puberty
- Surge centre present
- Controls pre-ovulatory surge in GnRH, leading to pre-ovulatory surge in LH
- Tonic secretions also at higher level due to frequency of secretion increasing
Describe the pre-pubertal HPG axis in the female
- Tonic centre stimulates LH pulses
- Low frequency of GnRHpulses, not enough for LH and FSH release at high levels
- Oestradiol secretion by ovarian follicles low
- Cannot stimulates GnRH neurones in surge centre
- Low leves of E2 have negative feedback on tonic centre - little GnRH release
Describe the transition to puberty in the HPG axis of the female
- Negative fedback effect of low E2 levels reduced
- Allows tonic centre to produce GnRH, increase in GnRH and thus increase in FSH and LH
- Increases E2 further, increases FSH and LH and more E2
- Eventually enough E2 to stimulate the surge centre
- i.e. trigger for puberty onset is loss of -ve feedback to tonic centre
Describe the HPG axis in male puberty onset
- Pre-puberty testosterone/oestradiol have negative feedback to GnRH
- GnRH neurones less sensitive to -ve feedback, GnRH increased, LH and FSH increased
- Puberty occurs
What is the average age for puberty in the male and female sheep?
Male:7 (6-9) months
Female: 7 (4-14) months
What is the average age for puberty in the male and female cow?
Male: 11 (7-18) months
Female: 11 (9-24) months
What is the average age for puberty in the male and female horse?
Male: 14 (10-24) months
Female: 18 (12-19) months
What is the average age for puberty in the male and female pig?
Male: 7 (5-8) months
Female: 6 (5-7) months
What is the average age for puberty in the male and female dog?
Male: 9 (5-12) months
Female: 12 (6-24) months
What is the average age for puberty in the male and female cat?
Male: 9 (8-10) months
Female: 8 (4-12) months
What is the main factor that influences seasonality?
- Melatonin and its effect in each species
- Influenced by photoperiod adn nutrition
Outline melatonin secretion
- Depends on photoperiod
- Sensed by retina and hypothalamus (
- Declining light (increased dark) increases melatonin secretion from the pineal gland
What is the effect of melatonin in short day breeders?
Stimulates reproduction, is stimulatory to GnRH release
What is the effect of melatonin in long day breeders?
Represses reproduction, is inhibitory to GnRH release
Describe melatonin secretion in short day breeders
- Nerve tract in retina stimulated by light
- Signal to hypothalamus at suprachiasmatic nucleus to going to superior cervical ganglion
- Nerve to pineal gland
- Stimulates inhibitory neurone which inhibits melatonin release
- Elevated activity in neurones, but inhibited melatonin release
- Opposite in cyclicity: less light, less stimualtion, more melatonin, GnRH release
Describe the role of kisspeptin neurones in seasonality
Kisspeptin stimulates GnRH release, FSH and LH release
Where are RFRP neurones found?
Within the hypothalamus
Describe the role of the RFRP neurones in seasonality
- RFRP neurones (amide related peptide) release RFRP3
- In long day breeder, RFRP3 stimulates neurones producing kisspeptin, stimulates GnRH release, FSH and LH release = cyclicity
- In short day breeders, RFRP3 inhibits kisspeptin neurones, low kisspeptin, low GnRH, FSH and LH
Give examples of factors that influence puberty
- Body size
- Nutrition
- Season born
- Photoperiod experienced at puberty
- Presence/absence of opposite sex just prior to puberty
- Density of same sex groups
Explain the role of body size in female puberty
- Amount of fat
- GnRH neurones sensitive to metabolic status
- 3 main types of pre-synaptic neurons affecting GnRH release
- Leptin, fatty acids and glucose thought to promote activity in kisspeptin neurones
- When threshold of “fatness” has been acheived, triggers signal from kisspeptin neurone to GnRH neurone, triggering GnRH release
Explain the role of nutrition on female puberty
- Higher plane of nutrition leads to earlier puberty, but over conditioned not ideal for breeding
- Moderate has later puberty onset but better for pregnancy and parturition
- Low plane has later puberty onset but may not be able to maintain pregnancy
How does leptin promote activity in kisspeptin neurones?
- Leptin produced by adipose tissue
- Acts on neuropetide Y neurones
- Synapses to kisspeptin neurones
Give strategies that can be used to advance/delay puberty/seasonality in domestic animasl
- Nutrition
- Hybrid vigour
- Photoperiod
- Endocrine studies (mostly experimental)
- Melatonin
- GnRH administration
- FSH/LH e.g. pregnant mare serum gonadotrophin
- Progesterone
Give a disadvantages of using GnRH to control puberty/seasonality
In deep anoestrus, pituitary will not be responsive to GnRH so would be pointless
Briefly outline the use of progesterone to advance seasonality in domestic animals
- In combination with PMSG
- Mimics luteal phase
- Stimulates follicles to get to maturation
Describe the HPG axis in long day breeders during the breeding season (female)
- Less melatonin produced
- Has stimulatory effect oon GnRH release
- GnRH release from hypothalamus, FSH and LH increased
- Increased inhibin production, shift from FSH to LH dependent
- Estradiol has positive feedback at certain level causing LH surge
- Progesterone from CL after ovulation suppresses GnRH release, suppresses axis
Describe the mare’s transition from winter anoestrus
- Takes 5-60 days
- Irregular oestrus
- Transition follicles present
- Ovulation will not occur until steroidogenic competence has increased through folliculogenesis stimulated by FSH
When do uterine involution and resumption of ovarian activity occur in the beef cow?
- Involution: 30 days
- Resumption: 50-60 days
When do uterine involution and resumption of ovarian activity occur in the dairy cow?
- Involution: 35-45 days
- Resumption: 18-25 days
When do uterine involution and resumption of ovarian activity occur in the bitch?
- Involution: 90 days
- Resumption: 135 days
When do uterine involution and resumption of ovarian activity occur in the ewe?
- Involution: 30 days
- Resumption: 180 days
When do uterine involution and resumption of ovarian activity occur in the mare?
- Involution: 14 days
- Resumption: 5-12 days
When do uterine involution and resumption of ovarian activity occur in the queen?
- Involution: 30 days
- Resumption: variable
What is ovarian rebound?
The return to cyclicity post-partum
Describe gestational anoestrus
- Prolonged high progesterone (CL or placental)
- Suppression of HPO axis
- Fewer follicular waves and no ovulation (except mare)
- Occasional oestrus behaviour
- Increased uterine size
What hormonal events occur following parturition?
- Decline in parturition
- Transient increase in oestrogens
What are some of the important post-partum events?
- Uterine involution
- Endometrial repair
- Expulsion of lochia
- Lactation/suckling
- Ovarian rebound
Describe the ovarian rebound mechanism
- Re-initiation of HPO axis (pit responds to GnRH again)
- Follicular wave emergence
- Resumption of full ovarian activity (increased sensitivity to GnRH, increased oestradiol, Increased LH pulse frequency, ovulation, short oestrus cycle)
What are the 2 main influencers of ovarian rebound?
- Uterus
- Metabolism
Describe the changes in hormonal balance pre and post calving
- Pre: increased oestradiol
- Post: decreased oestradiol and progesterone
- Following ovulation have increased progesterone
- As follicles develops, increased LH pulse frequency and then ovulation
What stimulates return to cyclicity in the sow?
Weaning
What factors influence ovarian rebound?
- Season
- Type of breeder e.g. seasonal, monooestrus
- Suckling
- Peri-parturient abnormalities (persistent CL)
- Milk yield/nutrition (NEB)
- Parity (esp primiparous)
What may cause extended anoestrus post-partum?
- Lactation
- Season
- Melatonin levels
How does lactation lead to extended anoestrus post-partum?
- Prolactin
- Prevents pregnancy before weaning
- Mammary stimulation/suckling suppresses GnRH
- Offspring influences e.g. visual, olfactory, auditory
- Weaning promotes GnRH/LH secretion
Describe ovarian rebound in the mare
- Rapid onset
- Rapid uterine involution
- Deteectable ovary activity within 2 days
- Foal heat - can establish pregnancy in this time
- Can be delayed
What may delay ovarian rebound in the mare?
- Season (foaling late in season)
- Maternal instinct (silent oestrus)
- “foal shy”
Describe ovarian rebound in the sow
- Suckling/weaning important
- Early follicular activity
- Prolactin suppresses LH = no ovulation
- Affected by length of lactation
- Weaning initiates LH surge within 7 days
Describe ovarian rebound in cats
- Oestrus inhibited often by lactation but is not uniform
- Anoestrus 2-8 weeks post-weaning
- Early weaning = early oestrus
Describe ovarian rebound in dogs
- Period of reproductive quiescence, not lactation dependent
- Around 135 days
- FSH/LH/oestrogen rise in late anoestrus
- Strongly influenced by nutrition
- Increased E2 at end of anoestrus
- Suppress FSH, shift to LH dependency, more E2
- Declines following ovulation
What cycling abnormalities can occur following parturition?
- Delayed onset of cyclicity
- Cessation of ovarian activity following initial resumption
- Ovarian pathologies e.g. follicular/luteal cysts, persistent CL
