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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
Anovulatory follicles
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
Prolonged dioestrus
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
Shortened dioestrus
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
Artificial control of anoestrus
- 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
Artificial control of transitional oestrus
- 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
Artificial control of oestrus
- 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
Artificial induction of ovulation
- 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
Artificial control of dioestrus
Can induce luteolysis with injection of PGF2a provided CL is >5 days old
33
Artificial control of whole cycle
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
Preparing barren mares for season
- 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
Preparing maiden mares for season
- Examine as early as possible at the beginning of season - Ensure normally developed external and internal genitalia
36
Preparing foaling mares for season
- 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
Venereal disease screening
Swabs taken from clitoral fossa and sinuses Placed in transport media (charcoal)
38
Recognised venereal pathogens
Tayorella equigenitalis Pseudomonas aeruginosa Klebsiella pneumoniae capsule types 1, 2, and 5
39
Teasing procedure and behaviour
Keen and sensible teaser stallion Oestrus mare is submissive (ears forward, leaning towards, straddling, crouching to urinate, clitoral winking)
40
Gynaecological examination
- Perineal conformation - Vaginal examination - Endometrial cytology and culture - Rectal palpation and US exam (- endometrial history, blood sampling, hysteroscopy, others)
41
Perineal conformation
- 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
Vaginal exam
- Use sterile vaginal speculum - View anterior vagina and cervix for signs of early oestrus
43
What does the cervix look like at the different points of the cycle
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
Endometrial cytology and culture
Routinely collected during early oestrus using sterile guarded swab Look for signs of uterine inflammation and infection
45
Which venereal bacteria is sensitive to light, so requiring charcoal media
Tayorella equigenitalis
46
Rectal palpation and US of uterus during oestrus
- Ideally no fluid present - Cartwheel appearance of wall, diminishes 24hrs before ovulation
47
Rectal palpation and US of ovaries during oestrus
- Typically bean shaped and vary in size - May feel hard in winter and softer in the breeding season
48
Rectal palpation and US of follicles during oestrus
- 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
Endometrosis/chronic degenerative endometrial disease
- 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
How long are spermatozoa viable in the female tract
72hrs
51
How long is the ova viable in the tract
up to 12 hrs
52
Site of fertilisation
Oviducts
53
What stimulates the embryos movement from oviduct to uterine horns
PGE2 secreted from the embryo at around day 5
54
Overall number of matings per oestrus on a stud farm
<1.1

Equine reproduction (14 decks)

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