Control of Reproduction in the Female Flashcards
What are the different definitions of puberty?
- age at first heat
- age at first ovulation
- age at which pregnancy is supported without negatively impacting the dam
Define age at first heat as a definition for puberty
- oestrus behaviour
- silent ovulation in cows and ewes not able to get pregnant
Define age at first ovulation as a definition for puberty
- although able to ovulate doesn’t mean she can carry a pregnancy to full term without detriment
- unwise to breed here as young mothers tend to have smaller offspring with parturition issues and impared foetal development
In which month does puberty start in each species?
- mare 14-18
- cow 10-12
- ewe/sow 6-7
- bitch 4-9
- queen 5-9
What can impact age of puberty?
- size of breed
- environment: season, pasture quality/availability, ruminants, seasonal breeders
- management: nutrition quality and availability, presence of opposite sex (cattle, pigs)
What are the different types of cyclicity?
- polyoestrus - regular cycles throughout the year
- seasonally polyoestrus - regular cycles in certain seasons
- monoestrus - one cycle in certain seasons of the year
How can different cyclicities be visualised?
looking at key hormones in cycle on a graph
- Y axis is oestrodiol concentrations
- peaks close to each ovulation
Which type of cyclicity is in each species?
- bitch - monoestrus
- queen - seasonal polyoestrus (Feb-Oct)
- sow, cow - polyoestrus
- ewe - seasonal polyoestrus (Sept-Jan)
- mare - seasonal polyoestrus (April-Oct)
What type of ovulator is each species?
- bitch, sow, cow, ewe, mare - spontaneous
- queen - induced
What is different about domestic bitch cycles?
can demonstrate 2-4 cycles per year
Describe anoestrus
- periods without cyclicity: seasonal, gestation, lactation
- most of the year in monoestrus
- doesn’t occur in mare
Why is lactation problematic in sows?
- polyoestrus to ensure multiple births per year
- tend to wean piglets too early
When does anoestrus occur in the mare?
- short anoestrus in 4-14days of lactation
What are the 2 main stages of the oestrus cycle?
- oestrus
- dioestrus
Describe oestrus
- sexually receptive
- oestradiol in high conc. from follicular growth
- peak oestradiol during ovulation then drops
- occurs prior to ovulation then drops in progesterone
Describe dioestrus
- not sexually receptive
- corpus luteum producing progesterone
- progesterone dominant hormone
Describe metoestrus and proestrus and when they occur
- occur in dioestrus
- metoestrus: oestrodiol decreases, progesteron increases
- proestrus: oestrodiol increases, progesterone decrease, formation of ovarian follicles
How does oestrus and the follicular phase link back to folliculogenesis?
- prior to ovulation
- drop in progesterone following luteolysis of CL
- increase in oestrodiol from developing follicle
- LH (theca interna): selection and development of follicles
- FSH + LH conversion of cholesterol to oestrodiol
- follicle development: FSH + LH -> increased oestrodiol
How does the CL link to dioestus and anoestrus?
- after ovulation
- progesterone increased
- dampening effect on system
- oestrodiol produced at basal levels
How long is oestrus in each species (days)?
- cow, ewe, sow - 2
- mare - 5
- bitch - 9
- queen - 10
How long is dioestrus in each species (days)?
- cow - 19
- sow - 20
- ewe - 15
- mare - 16
- bitch 60-90
- queen 14-21
how long is the entire oestrus cycle in each species (days)?
- cow, sow, mare - 21
- ewe - 17
- bitch ~6months
- queen - 20-40
Describe the endocrine changes in the oestrus cycle
HPA axis:
- hypothalamus produces GnRH
- pituitary produces FSH&LH
- ovary produces oestrogens and progesterone from CL formation
- uterus produces prostaglandin F2alpha and E2
Describe the role of the hypothalamus in oestrus
- acts on anterior pituitary
- region of brain controlling thist, hunger and temp
- connected via neurons and capillary network called hypothalamohypophysial portal system
Describe the role of the pituitary gland in oestrus
- master gland
- anterior pituitary secretes FSH to granulosa and LH to theca interna
- FSH converts cholesterol to androstenedione for follicle recruitment
- LH converts androstenedione to oestrodiol for selection and dominance
Describe the positive and negative feedback in oestrus
- progesterone has a negative feedback effect on the whole system
- PGF2alpha - negative on CL - luteolysis
- overall the system is positive feedback
Describe oestrus in seasonal polyoestrus breeders
- controlled by pineal gland
- light detected by photoreceptors on retina - neural connection to hypothalamus which sends signal to pineal
- in periods of darkness: pineal produces melatonin from pinealocytes
- excites HPG axis in short day breeders, increasing GnRH
- opposite in long day breeders
Describe the first ovulation after anoestrus in seasonal breeders such as sheep
- not uncommon for it to be silent
- follicle developes and ovulates but no secondary oocyte
- often no oestrus behaviour
Describe the role of GnRH
- peptide hormone
- 80% goes to anterior pituitary, physiological effect
- 20% to CNS, behavioural effect
- secreted by hypothalamus, travels by hypothalamohypophyseal portal system to anterior pituitary
Why are GnRH levels difficult to quantify?
travels via neuronal network
Describe the episodic release of GnRH and reproductive hormones
- basal secretion on pituitary gland in small pulses
- low oestrodiol - negative feedback
- high progesterone
- preovulatory surge of GnRH - increases in follicular phase
- leads to low progesterone and high oestradiol
- oestradiol positive feedback on hypothalamus to increase GnRH
Describe the role of FSH in the cycle
- GnRH increase leads to increased FSH
- increased progesterone leads to decreased FSH
- as ovulation approaches, increased GnRH and FSH
- follicle size increases accompanied by LH - decreased oestradiol
Describe FSH in monophasic animals
- FSH increase starts on D13 (ewe) or D14/15 (cow, sow)
- 1 main peak just prior to ovulation
- short pre-ovulatory follicle development cycle
Describe FSH in the mare
- prolonged peak
- long follicle development cycle - main increase from D14/15
Describe LH in the cycle
- negative feedback on FSH
- secreted by anterior pituitary on theca cells on follicle in ovary via circulation, triggered by GnRH
- drives follicle development/recruitment and oestrodiol secretion from theca cells
- causes ovulation and CL formation
- removes miotic inhibitors from primary oocyte allowing meiosis I to complete
- controls GnRH increase - increases LH
- controls E increase - increases LH
- controls progesterone increase - decreases LH
Describe LH prior to ovulation
- GnRH, progesterone, oestrodiol increase
- 1 large pre-ovulatory peak: D16 (ewe), D18 (mare), D20 (cow, sow)
- most mammals - short peak
- mares: prolonged peak day after ovulation
Describe the role of oestradiol
- drives oestrus
- increases FSH and LH: positive feedback on LH, negative for FSH
- acts on CNS
- secreted by large follicles
When does progesterone plateu?
- luteal phase
- mare, cow, sow: D6-15
- ewe, queen: D6-13
- bitch: D10 onwards
What is the role of progesterone?
- prepare for pregnancy: inhibits HPG axis, reduces LH and FHS
- if pregnant: CL and progesterone remains
Describe what happens to progesterone if not pregnant?
- reduction in progesterone resulting in
- FSH increase - follicle development
- oestrodiol increase - start next oestrus
- LH increase - induce ovulation
- PGF2a knocks out CL
Describe PGF2a
- prostaglandin F2 alpha
- ends luteul phase - reduces progesterone and ends inhibition of HPG axis
- allows ovulation and oestrus to occur
- 21D cycle: D14/15
- 17D cycle: D13
Describe the genital tract changes in dioestrus
- progesterone influence to prepare for implantation/pregnancy
- cervix tight, white, dry, reduced secretion
- uterus: wall thickens, epithelium proliferates (cuboidal), increased endometrial gland activity, increased tone
Describe the genital tract changes in oestrus
- oestrogen influence
- aim to allow passage of penis, encourage movement of sperm to ovulated ova
- vulva swells, reddening (not all species)
- cervix loose, red/pink and secretions
- uterus: wall thinner, reduced gland activity, flaccid, myometrial contractions
What are the behavioural changes in dioestrus?
hostility to male
What are the general behavioural differences in oestrus?
- increased locomotion
- docility
- acceptance of male
- urination stance, raised tail
- mounting activity - not true sign but indicative
What are the species differences for behavioural changes in oestrus?
- mare: lengthening and eversion of vulva/clitoris
- sow - lordosis
- queen - lordosis and vocalisation
