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Equine reproduction > The oestrus cycle > Flashcards

The oestrus cycle Flashcards

1
Q

Official recognised TB birth date

A

January 1st

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2
Q

Official TB covering/breeding season

A

Feb 15th to July 15th

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3
Q

Distinct breeding season UK

A

April to October

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4
Q

Seasonal periods of the year WRT oestrus

A

Breeding season April-October
Period of sexual quiescence, anoestrous November-March
Transitional phase (Spring oestrus)

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5
Q

Main extero-receptive factors to renewed ovarian cyclicity

A
  • Increasing daylight
  • Increasing ambient temperature
  • Increasing food supply
  • Pheromonal effect of the stallion
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6
Q

How long does the oestrus cycle last

A

21-23 days

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7
Q

How long does oestrus (follicular phase) last

A

2-4 days

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8
Q

How long does dioestrus
(luteal phase) last

A

15-17 days in peak breeding season but up to several weeks during transitional phase

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9
Q

How long after foaling is mare ready to start first oestrous cycle

A

7-9 days

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10
Q

Oestrus (follicular phase)

A

Very variable
Prolonged in spring and autumn, shortest mid-season
Uterine wall is flaccid and oedematous
Relaxation of the cervix - moist, pink/red

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11
Q

Dioestrus (luteal phase)

A

Less variable
High incidence of spontaneous prolongation in the abscence of pregnancy
Aggressive, ears back, squealing, striking, kicking at stallion
increased tone in the uterine wall as the uterus prepares for implantation
Cervix closes and if firm, dry, and pale pink/white

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12
Q

Ovulation

A

Cohort of 8-12 follicles of >1cm develop
Most regress by atresia
Mature follicle of 4-5cm ovulates

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13
Q

Rate of twin ovulations in TBs

A

20-25%

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14
Q

Twin conception rate

A

5-8%

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15
Q

Changes inducing cyclicity from anoestrous

A
  • Melatonin secretion from pineal gland decreases in response to daylight length
  • Increased pulsatile secretions of GnRH from hypothalamus
  • Stimulates release of FSH and/or LH from pituitary
  • FSH released in 10-12 day episodic surges throughout breeding season stimulates follicular growth
  • Developing follicles produce oestrogen and inhibin
  • Rising blood [oestrogen] stimulates pituitary to produce LH
  • LH stimulates maturation of follicles and ova to ovulation
  • Progesterone secreted by the CL
  • Falling blood oestrogen and rising progesterone levels responsible for dioestrus behaviour
  • Falling inhibin levels stimulate production of FSH and so more follicles develop
  • About 14 days after ovulation endometrial glands produce PGF2a which cause luteolysis and destroy CL so progesterone levels fall - end of dioestrus
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16
Q

What does melatonin do

A

Inhibits the release of GnRH from the hypothalamus

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17
Q

When is the peak concentration of LH

A

1-2 days after ovulation

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18
Q

When is the peak concentration of oestrogen in the blood

A

1-2 days before ovulation

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19
Q

What is oestrogen mainly secreted as

A

Oestradiol-17B

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20
Q

When do levels of progesterone peak

A

As early as 5 days after ovulation
Fall sharply during days 14-16 due to uterine prostaglandin F2a

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21
Q

Prolonged spring oestrus

A

In transitional phase
Often maidens
Erratic or persistent oestrus behaviour for many weeks before ovulation
Probably insufficient release of LH from the partially awakened pituitary

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22
Q

Silent oestrus

A

Produce a follicle that grows and ovulates normally but no accompanying cervical changes or oestrus behaviour
May be due to lack of oestrogen receptors in reproductive tract in young animals

23
Q

Split oestrus

A

Not common
One follicle grows for 2-3 days and mare shows normal signs of oestrus
That follicle then regresses and mare goes out of oestrus
Another follicle then grows normally to ovulation and the mare returns to oestrus

24
Q

Twin ovulation

A

High occurrence (about 25% TBs)
Very rare in native ponies

25
Q

Anovulatory follicles

A

Ovulation failure
Difficult to predict
May have ‘Snow storm’ appearance of echoic particles in the follicular fluid - likely to be result of haemorrhage - may organise to a cobweb network so could be confused with granulosa cell tumour
Respond well to prostaglandin

26
Q

Prolonged dioestrus

A

Relatively common, especially later in season
May last for 2-3 mo
Likely due to inadequate PGF2a release or deficiency of receptors in CL
Treat with exogenous IM injection of PGF2a

27
Q

Shortened dioestrus

A

Mare returns to oestrus every 10-12 days due to short lifespan of CL
Premature release of uterine PGF2a
Usually caused by endometrial inflammation resulting from uterine infection

28
Q

Artificial control of anoestrus

A
  • Artificial lighting to initiate transitional phase
  • Increasing warmth and plane of nutrition, and contact with stallion stimulates cyclic activity
  • Low doses of GnRH by injections or slow release implant
29
Q

Artificial control of transitional oestrus

A
  • Oral progesterone (regumate) or IM progestagens with oestradiol for 10 days
  • Followed by luteolytic dose of prostaglandin on the last day
  • Stimulates a surge of LH
30
Q

Artificial control of oestrus

A
  • Can induce behavioural oestrus in anoestrus mares with a single IM injection of oestradiol benzoate - use with care so not to inhibit follicular growth
31
Q

Artificial induction of ovulation

A
  • Hastened with single IV injection of hCG, used to avoid repeat coverings
  • DDesorelin (Ovuplant) is a GnRH analogue in implant form, induces ovulations during oestrus
32
Q

Artificial control of dioestrus

A

Can induce luteolysis with injection of PGF2a provided CL is >5 days old

33
Q

Artificial control of whole cycle

A

Can use oral progesterone for 10 days followed by injection of PGF2a on day 10 to synchronise ovulation within 2-3 days for all treated mares

34
Q

Preparing barren mares for season

A
  • Thorough exam after the end of the breeding season before they go into winter anoestrus
  • Sort out any persistent genital problems and allow time for recovery
35
Q

Preparing maiden mares for season

A
  • Examine as early as possible at the beginning of season
  • Ensure normally developed external and internal genitalia
36
Q

Preparing foaling mares for season

A
  • Should resume cycling 7-10 days after foaling
  • Examine at this stage to determine readiness for mating
  • <10% mares considered suitable for mating at their foal heat
37
Q

Venereal disease screening

A

Swabs taken from clitoral fossa and sinuses
Placed in transport media (charcoal)

38
Q

Recognised venereal pathogens

A

Tayorella equigenitalis
Pseudomonas aeruginosa
Klebsiella pneumoniae capsule types 1, 2, and 5

39
Q

Teasing procedure and behaviour

A

Keen and sensible teaser stallion
Oestrus mare is submissive (ears forward, leaning towards, straddling, crouching to urinate, clitoral winking)

40
Q

Gynaecological examination

A
  • Perineal conformation
  • Vaginal examination
  • Endometrial cytology and culture
  • Rectal palpation and US exam
    (- endometrial history, blood sampling, hysteroscopy, others)
41
Q

Perineal conformation

A
  • Wash with clean water - no disinfectants
  • Vulva should be on a vertical line with the anus above
  • Bony level of the pelvis should be at the top of the vulva
  • Immediately inside the floor of the vulva is the clitoris which lies within a fossa
  • Walls of vagina usually in apposition
  • 3 important seals: vulva, vagina, cervix
42
Q

Vaginal exam

A
  • Use sterile vaginal speculum
  • View anterior vagina and cervix for signs of early oestrus
43
Q

What does the cervix look like at the different points of the cycle

A

Oestrus: moist, pink/reddened, oedematous, relaxed, often flopped onto vaginal floor
Dioestrus: tight, erect, protruding into the vagina with a tudor rose appearance
Anoestrus: pale, flaccid, sometimes gaping open
Pregnancy: tight, pale, erect, a glazed appearance

44
Q

Endometrial cytology and culture

A

Routinely collected during early oestrus using sterile guarded swab
Look for signs of uterine inflammation and infection

45
Q

Which venereal bacteria is sensitive to light, so requiring charcoal media

A

Tayorella equigenitalis

46
Q

Rectal palpation and US of uterus during oestrus

A
  • Ideally no fluid present
  • Cartwheel appearance of wall, diminishes 24hrs before ovulation
47
Q

Rectal palpation and US of ovaries during oestrus

A
  • Typically bean shaped and vary in size
  • May feel hard in winter and softer in the breeding season
48
Q

Rectal palpation and US of follicles during oestrus

A
  • Development continues until follicle reaches about 3-6cm
  • Circular in chape and deformable with gentle pressure
  • Become pie shaped within 24-48hrs of ovulation
    48hrs after mating examine again:
  • ovarian follicle still fluctuant, non-painful, and anechoic: ovulation has not occurred
  • Ovarian follicle remains fluctuant, but is hyperechoic or anechoic with hyperechoic particles, may be painful: confirms ovulation and suggests corpus haemorrhagicum
  • Ovarian follicle is hard, non-painful, hyperechoic: confirms ovulation, suggests CL
49
Q

Endometrosis/chronic degenerative endometrial disease

A
  • Mares up to 9yrs should have no endometrosis
  • 9-13yrs: mild endometrosis, 90% foaling rate
  • 13-17yrs: moderate endometrosis, 70% foaling rate
  • 17+ yrs: severe endometrosis, <10% foaling rate
50
Q

How long are spermatozoa viable in the female tract

A

72hrs

51
Q

How long is the ova viable in the tract

A

up to 12 hrs

52
Q

Site of fertilisation

A

Oviducts

53
Q

What stimulates the embryos movement from oviduct to uterine horns

A

PGE2 secreted from the embryo at around day 5

54
Q

Overall number of matings per oestrus on a stud farm

A

<1.1

Equine reproduction (14 decks)

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