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ASC261 > Oestrous cycles > Flashcards

Oestrous cycles Flashcards

1
Q

When does the oestrous cycle begin?

A

Begins at puberty & continues throughout the female adult life

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2
Q

What are occasional interruptions in oestrous cycles?

A
  • pregnancy
  • lactation
  • seasonal effects in some spp.
  • inadequate nutrition
  • environmental stress
  • uterine infection
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3
Q

What are interruptions of oestrous called?

A

anoestrus

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4
Q

Behavioural events of oestrus…?

A

sexual receptivity

copulation (usually prior to ovulation)

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5
Q

Endocrine events of oestrus…?

A

increase in gonadotropins (FSH & LH via GnRH)

increase in oestrogen

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6
Q

Physical events of oestrus…?

A

follicular phase

ovulation

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7
Q

What are the 2 main oestrous cycle phases…? What occurs in each phase?

A 
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
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8
Q

Draw phases (luteal/follicular, & pro-, oestrus, met-, dioestrus) of cow cycle…include hormones & days of cycle

A

slide 6 & 8…

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9
Q

Phases can be divide into 4 stages. What are they?

A

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

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10
Q

Describe in detail the events during pro-oestrus… mention which behaviour is present.

A

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

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11
Q

Describe in detail the events during oestrus…

A

Most recognisable stage
- behavioural symptoms due to OESTROGEN
- willingness to allow mating “standing oestrus” & “lordosis”
Oestrogen reaches threshold
- behavioural oestrus
- OVULATION

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12
Q

Describe in detail the events during metoestrus…

A

Period between ovulation & formation of CL
- E2 & P4 present
LUTENISATION
- newly ovulated follicle -> remodelling
- formation of functioning endocrine gland
- P4 continues to increase

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13
Q

Describe in detail the events during dioestrus…

A

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!

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14
Q

Which animals are polyoestrus…?

A

cows
queens
pigs
rodents

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15
Q

Which animals are seasonally polyoestrus…?

A 
Long & short day breeders
mares
ewes
does
elks
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16
Q

Which animals are monoestrus…?

A

dogs (domestic bitches cycle at any time of year)
wolves
bears
foxes

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17
Q

Re. cycle of the queen…queen enters oestrus how often?

A

every 17 days, for 9 days

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18
Q

Re. cycle of the queen…what happens if copulation does not occur?

A

queen enters postoestrus (low E2 & P4 levels), then oestrus a few days later

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19
Q

Re. cycle of the queen…What is meant by ‘induced ovulators’?

A

mating is required for ovulation

NO CL is formed

20
Q

Re. cycle of the queen…Mating results in ovulation & …?

A

CL formation
Progesterone
60 days gestation/CL function

21
Q

Mean length of estrous cycle & mean duration of oestrus in a bitch?

A

6 mo & 9d

22
Q

Mean length of estrous cycle & mean duration of oestrus in a cow?

A

21d & 15h

23
Q

Mean length of estrous cycle & mean duration of oestrus in a ewe?

A

17d & 30h

24
Q

Mean length of estrous cycle & mean duration of oestrus in a mare?

A

21d & 7d

25
Q

Mean length of estrous cycle & mean duration of oestrus in a queen?

A

17d & 9d

26
Q

Mean length of estrous cycle & mean duration of oestrus in a sow?

A

21d & 50h

27
Q

Define anoestrus…

A 
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
28
Q

What is gestational anoestrus?

A

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

29
Q

What is lactational anoestrus?

A

Prevention of new pregnancy before weaning

  • most mammalian spp. for variable time
  • lactational anoestrus rare in mare & alpaca
30
Q

Complete cyclicity suppression in which animal?

A

sow - return to oestrus after weaning & ovulation 4-8 days after weaning

31
Q

How long can lactational anoestrus last in a cow?

A

up to 60 days post partum (depends on freq. of suckling)

≤2/day -> return to cyclicity

32
Q

T or F - lactational anoestrus is affected only by neural stimulation

A

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)

33
Q

LA in dairy cows when calves removed 24-48 hours post partum…

A

no LA observed

34
Q

Does the bitch display LA?

A

No, only post partum anoestrus 5-6 months which is independent of lactation

35
Q

LA in the queen…

A

individual variation
cyclicity returns 2-3 w after weaning
some return to oestrus 7-10d post partum

36
Q

What is seasonal anoestrus?

A

Prevents parturition during periods of year when survival of embryo/neonate would be low

37
Q

Give 2 examples of seasonal anoestrus

A

eg. 1: embryo attachment compromised in hot weather

eg. 2: parturition in spring (increased feed availability)

38
Q

Seasonal anoestrus is controlled by …?

A

photoperiod

- short vs long day breeders

39
Q

Seasonal anoestrus onset similar to onset of …?

A

puberty

40
Q

Describe the events of seasonal anoestrus in long day (spring/summer) breeders…

A

++daylight -> ++firing excitatory neurons in retina -> ++excitation from superior cervical ganglion (SCG) -> ++inhibition of pineal gland -> decreased melatonin -> GnRH -> decreased LH & FSH -> anoestrus

41
Q

Describe the events of cyclicity in short day (autumn/winter) breeders…

A

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

42
Q

How is the return of seasonal cyclicity similar to puberty?

A

GnRH secretion -> LH & FSH release from pituitary

43
Q

What is the most important signal to seasonal cyclicity? Key hormone involved?

A

Photoperiod - melatonin

44
Q

Describe a silent ovulation?

A

Ovulation minus behavioural oestrus (possibly due to no P4 priming) -> no CL at end of anoestrus

45
Q

Anoestrus due to -ve energy balance leads to…?

A 
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
46
Q

To eliminate true anoestrus, we must…?

A

improve nutrition
remove offspring/end lactation
eliminate stress
consider seasonal effects

47
Q

To eliminate apparent anoestrus, we must…?

A

improve oestrus detection & pregnancy detection methods

ASC261 (17 decks)

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