Oestrous cycles Flashcards
When does the oestrous cycle begin?
Begins at puberty & continues throughout the female adult life
What are occasional interruptions in oestrous cycles?
- pregnancy
- lactation
- seasonal effects in some spp.
- inadequate nutrition
- environmental stress
- uterine infection
What are interruptions of oestrous called?
anoestrus
Behavioural events of oestrus…?
sexual receptivity
copulation (usually prior to ovulation)
Endocrine events of oestrus…?
increase in gonadotropins (FSH & LH via GnRH)
increase in oestrogen
Physical events of oestrus…?
follicular phase
ovulation
What are the 2 main oestrous cycle phases…? What occurs in each phase?
Follicular phase (Oestrus) - follicle growth & dev. - oestrogen dominant - ovulation (signals end of follicular phase) Luteal phase (Dioestrus) - Corpus Luteum formation - progesterone dominant - Luteolysis by Prostaglandin F2alpha
Draw phases (luteal/follicular, & pro-, oestrus, met-, dioestrus) of cow cycle…include hormones & days of cycle
slide 6 & 8…
Phases can be divide into 4 stages. What are they?
Pro-oestrus - formation of follicles & increased E2 secretion
Oestrus - sexual receptivity & peak E2 secretion
Metoestrus - Corpus Luteum (CL) formation & increasing P4 secretion
Dioestrus - CL dominance & secretion of P4
Describe in detail the events during pro-oestrus… mention which behaviour is present.
Progesterone declines
- luteolysis -> due to PGF2alpha from uterus
Finishes at onset of oestrus
Lasts 2-5 days
- endocrine transition from P4 dominance to E2 dominance (LH & FSH are responsible for this transition)
Behaviour present: females attract/tease males but do not allow them to mate as aren’t quite ready yet
Describe in detail the events during oestrus…
Most recognisable stage
- behavioural symptoms due to OESTROGEN
- willingness to allow mating “standing oestrus” & “lordosis”
Oestrogen reaches threshold
- behavioural oestrus
- OVULATION
Describe in detail the events during metoestrus…
Period between ovulation & formation of CL
- E2 & P4 present
LUTENISATION
- newly ovulated follicle -> remodelling
- formation of functioning endocrine gland
- P4 continues to increase
Describe in detail the events during dioestrus…
Max P4 function
- CL fully functional
- P4 dominance
- prepares uterus for early embryonic development
Ceases with LUTEOLYSIS
- duration of dioestrus directly related to life span of CL
Will NOT accept mating during this stage!
Which animals are polyoestrus…?
cows
queens
pigs
rodents
Which animals are seasonally polyoestrus…?
Long & short day breeders mares ewes does elks
Which animals are monoestrus…?
dogs (domestic bitches cycle at any time of year)
wolves
bears
foxes
Re. cycle of the queen…queen enters oestrus how often?
every 17 days, for 9 days
Re. cycle of the queen…what happens if copulation does not occur?
queen enters postoestrus (low E2 & P4 levels), then oestrus a few days later
Re. cycle of the queen…What is meant by ‘induced ovulators’?
mating is required for ovulation
NO CL is formed
Re. cycle of the queen…Mating results in ovulation & …?
CL formation
Progesterone
60 days gestation/CL function
Mean length of estrous cycle & mean duration of oestrus in a bitch?
6 mo & 9d
Mean length of estrous cycle & mean duration of oestrus in a cow?
21d & 15h
Mean length of estrous cycle & mean duration of oestrus in a ewe?
17d & 30h
Mean length of estrous cycle & mean duration of oestrus in a mare?
21d & 7d
Mean length of estrous cycle & mean duration of oestrus in a queen?
17d & 9d
Mean length of estrous cycle & mean duration of oestrus in a sow?
21d & 50h
Define anoestrus…
Without cyclicity - inactive ovaries - no ovulations - no functional CL Insufficient GnRH - no gonadotrophin secretion - no ovarian stimulation True vs apparent anoestrus - failure to detect oestrus - failure to detect pregnancy
What is gestational anoestrus?
Natural anoestrus (most common)
Inhibition of GnRH by progesterone
- -ve feedback on GnRH neurons -> no cyclicity during pregnancy
- occasional behavioural oestrus (3-5%)
Animal remains in anoestrus after parturition
- uterine involution & repair
- lactational anoestrus
What is lactational anoestrus?
Prevention of new pregnancy before weaning
- most mammalian spp. for variable time
- lactational anoestrus rare in mare & alpaca
Complete cyclicity suppression in which animal?
sow - return to oestrus after weaning & ovulation 4-8 days after weaning
How long can lactational anoestrus last in a cow?
up to 60 days post partum (depends on freq. of suckling)
≤2/day -> return to cyclicity
T or F - lactational anoestrus is affected only by neural stimulation
false - suppression of LH alone does not cause LA. Cow/calf interactions (visual/olfactory/auditory) - must be cow’s own calf (alien calf causes LH secretion)
LA in dairy cows when calves removed 24-48 hours post partum…
no LA observed
Does the bitch display LA?
No, only post partum anoestrus 5-6 months which is independent of lactation
LA in the queen…
individual variation
cyclicity returns 2-3 w after weaning
some return to oestrus 7-10d post partum
What is seasonal anoestrus?
Prevents parturition during periods of year when survival of embryo/neonate would be low
Give 2 examples of seasonal anoestrus
eg. 1: embryo attachment compromised in hot weather
eg. 2: parturition in spring (increased feed availability)
Seasonal anoestrus is controlled by …?
photoperiod
- short vs long day breeders
Seasonal anoestrus onset similar to onset of …?
puberty
Describe the events of seasonal anoestrus in long day (spring/summer) breeders…
++daylight -> ++firing excitatory neurons in retina -> ++excitation from superior cervical ganglion (SCG) -> ++inhibition of pineal gland -> decreased melatonin -> GnRH -> decreased LH & FSH -> anoestrus
Describe the events of cyclicity in short day (autumn/winter) breeders…
decreased daylight -> decreased firing excitatory neurons in retina -> decreased excitation from superior cervical ganglion (SCG) -> decreased inhibition of pineal gland -> ++melatonin -> ++GnRH -> ++LH & FSH -> cyclicity
How is the return of seasonal cyclicity similar to puberty?
GnRH secretion -> LH & FSH release from pituitary
What is the most important signal to seasonal cyclicity? Key hormone involved?
Photoperiod - melatonin
Describe a silent ovulation?
Ovulation minus behavioural oestrus (possibly due to no P4 priming) -> no CL at end of anoestrus
Anoestrus due to -ve energy balance leads to…?
Sustained periods of anoestrus - return in favourable conds. No GnRH pulses form hypo. -> lengthened lactational anoestrus Primiparous (1st time pregnant) females - high energy requirements for lactation - delayed post partum
To eliminate true anoestrus, we must…?
improve nutrition
remove offspring/end lactation
eliminate stress
consider seasonal effects
To eliminate apparent anoestrus, we must…?
improve oestrus detection & pregnancy detection methods
