Oestrous cycles

Question 1

When does the oestrous cycle begin?

Answer 1

Begins at puberty & continues throughout the female adult life

Question 2

What are occasional interruptions in oestrous cycles?

Answer 2

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

Question 3

What are interruptions of oestrous called?

Answer 3

anoestrus

Question 4

Behavioural events of oestrus…?

Answer 4

sexual receptivity

copulation (usually prior to ovulation)

Question 5

Endocrine events of oestrus…?

Answer 5

increase in gonadotropins (FSH & LH via GnRH)

increase in oestrogen

Question 6

Physical events of oestrus…?

Answer 6

follicular phase

ovulation

Question 7

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

Answer 7

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

Question 8

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

Answer 8

slide 6 & 8…

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

Describe in detail the events during oestrus…

Answer 11

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

Question 12

Describe in detail the events during metoestrus…

Answer 12

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

Question 13

Describe in detail the events during dioestrus…

Answer 13

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!

Question 14

Which animals are polyoestrus…?

Answer 14

cows
queens
pigs
rodents

Question 15

Which animals are seasonally polyoestrus…?

Answer 15

Long & short day breeders
mares
ewes
does
elks

Question 16

Which animals are monoestrus…?

Answer 16

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

Question 17

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

Answer 17

every 17 days, for 9 days

Question 18

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

Answer 18

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

Question 19

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

Answer 19

mating is required for ovulation

NO CL is formed

Question 20

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

Answer 20

CL formation
Progesterone
60 days gestation/CL function

Question 21

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

Answer 21

6 mo & 9d

Question 22

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

Answer 22

21d & 15h

Question 23

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

Answer 23

17d & 30h

Question 24

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

Answer 24

21d & 7d

Question 25

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

Answer 25

17d & 9d

Question 26

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

Answer 26

21d & 50h

Question 27

Define anoestrus...

Answer 27

``` 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 ```

Question 28

What is gestational anoestrus?

Answer 28

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

Question 29

What is lactational anoestrus?

Answer 29

Prevention of new pregnancy before weaning - most mammalian spp. for variable time - lactational anoestrus rare in mare & alpaca

Question 30

Complete cyclicity suppression in which animal?

Answer 30

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

Question 31

How long can lactational anoestrus last in a cow?

Answer 31

up to 60 days post partum (depends on freq. of suckling) | ≤2/day -> return to cyclicity

Question 32

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

Answer 32

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)

Question 33

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

Answer 33

no LA observed

Question 34

Does the bitch display LA?

Answer 34

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

Question 35

LA in the queen...

Answer 35

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

Question 36

What is seasonal anoestrus?

Answer 36

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

Question 37

Give 2 examples of seasonal anoestrus

Answer 37

eg. 1: embryo attachment compromised in hot weather | eg. 2: parturition in spring (increased feed availability)

Question 38

Seasonal anoestrus is controlled by ...?

Answer 38

photoperiod | - short vs long day breeders

Question 39

Seasonal anoestrus onset similar to onset of ...?

Answer 39

puberty

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

How is the return of seasonal cyclicity similar to puberty?

Answer 42

GnRH secretion -> LH & FSH release from pituitary

Question 43

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

Answer 43

Photoperiod - melatonin

Question 44

Describe a silent ovulation?

Answer 44

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

Question 45

Anoestrus due to -ve energy balance leads to...?

Answer 45

``` 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 ```

Question 46

To eliminate true anoestrus, we must...?

Answer 46

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

Question 47

To eliminate apparent anoestrus, we must...?

Answer 47

improve oestrus detection & pregnancy detection methods