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Y3 MOD Reproductive > The Mare > Flashcards

The Mare Flashcards

1
Q

What is a mare?

A

A female horse 4 or more years old

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2
Q

A horse younger than 4 years old is called?

A

A filly

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3
Q

Describe the type of breeders horses are

A

A long day, seasonally polyoestrus breeder.
Most mares in anoestrus over winter
Increasing day length brings about a breeding season lasting from spring to late summer.

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4
Q

What happens at the start and end of each breeding season?

A

Transition period of irregular cycling

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5
Q

When does puberty begin?

A

Occurs between 12-24 months, cycling occurs for the rest of the mares life although fertility may decline

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6
Q

How long is the oestrus cycle?

A

21 days

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7
Q

What are the lengths of dioestrus and oestrus?

A

Dioestrus consistent at 16-17 days.
Oestrus lasts 4-6 days – tending to be longer and weaker in early breeding season and shorter and stronger later in the season.

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8
Q

What occurs within 24 hours of ovulation?

A

The mare will not be receptive to the stallion

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9
Q

Describe the oestrus cycle in a mare up to ovulation

A
  • Waves of follicles develop during dioestrus: reaching 25mm in size, but then regress
  • When hormonal conditions are correct one follicle is “recruited” and develops into a dominate follicle which will ovulate.
  • Oestrus is induced by the dominant follicle
  • Ovulation occurs
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10
Q

What is produced by the dominant follicle?

A

Oestrogens which induce oestrus

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11
Q

When does ovulation occur?

A

When the dominant follicle reaches >35 mm. Oestrus ends within 24 hours after ovulation

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12
Q

Describe the oestrus cycle following ovulation

A
  • Oestrus ends within 24 hours of ovulation
  • After ovulation the ovulation site first becomes a corpus haemorrhagicum and then this turns into a corpus luteum
  • The CL is refractory to the effects of prostaglandins for 3-4 days after formation.
  • After about 15 days the endometrium releases prostaglandin and causes luteolysis – oestrus will commence again
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13
Q

Which hormone is secreted by the corpus luteum?

A

Progesterone

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14
Q

How long can the transitional period last?

A

Up to 6 weeks

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15
Q

Describe the main features of the transitional period

A
  • A period of change from anoestrus to regular cyclical activity
  • Ovaries posses multiple small follicles 10-25mm in diameter, “bunch of grapes ovaries”
  • Transitional follicles do not ovulate and eventually regress
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16
Q

Describe mares in the transitional period

A

Mares may show no signs of oestrus, erratic oestrus behaviour or constant oestrus behaviour
Mares mated in the transitional period will not conceive

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17
Q

How does luteolysis occur?

A

Prostaglandins produced by the endometrium

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18
Q

How can prostaglandins manipulate oestrus?

A

Induce luteolysis in receptive corpus luteum.

Oestrus will commence 3-5 days post injection – but variable depending on stage of breeding season.

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19
Q

What are some side effects of prostaglandins?

A

Transient colic, sweating, diarrhoea etc

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20
Q

How can progestagens manipulate oestrus?

A
  • Given orally: suppress oestrus
  • Withdrawal of treatment leads to rebound ovarian activity – useful to shorten length of spring transitional period.
  • Intra- vaginal devices (PRID) sometimes used off-licence
  • Sometimes used to maintain high risk pregnancies
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21
Q

How can oestrogens manipulate oestrus?

A

Induce behavioural signs of oestrus but not true oestrus.

Only useful for maintaining “teaser mares” for AI collection.

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22
Q

Name the drug that if give, will induce the dominant follicle (>35mm) to ovulate within 24 hours.

A

Chorionic gonadotropin

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23
Q

What is deslorelin?

A

A GnRH analogue

24
Q

What is the use of deslorelin?

A

Hormone implant given sub-cut when follicle >30mm – should induce ovulation within 48 hours in most mares

25
Q

How can the photoperiod be used to manipulate oestrus?

A
  • Breeding season can be brought forward by use of artificial light over winter
  • Many protocols but providing 16 hours of light and 8 hours dark from 2-4 weeks before Winter solstice commonly used.
  • Light intensity important
  • Mares start to ovulate 8-10 weeks later
26
Q

When might oestrus suppression be requested?

A

For mares whose sexual behaviour makes life difficult for owner

27
Q

Give some examples of behaviours that may lead to owners wanting oestrus suppression of their mares?

A
  • Behaviour problem may actually be non-sexual in nature (poor training, orthopaedic pain etc)
  • Behaviour maybe sexual but not hormone related (eg social “flirting” even if out of oestrus)
  • Some mare sex hormones also produced by brain and adrenals
  • Treatment may damage potential future breeding career
28
Q

What are the methods for suppressing oestrus in mares?

A
  • Long term progestagens
  • Intra-uterine devices: replicate pregnancy and suppress oestrus
  • Anti-GnRH vaccine
  • Repeat oxytocin injections to induce a long term CL
  • Plant oils infused into oestrus
  • Put into foal
  • Ovariectomy
29
Q

How should mating be timed for conception in horses

A
  • Oestrus behaviour ceases within 24 hours of ovulation: mare no longer receptive to stallion.
  • Unfertilised oocyte viable for only 12 hours post ovulation.
  • Matings after ovulation have very poor conception rates.
  • Spermatozoa reach oviduct within hours of insemination.
  • Spermatozoa viable for up to 48 hours once in the mares reproductive tract.

Therefore serve mares 24-48 hours prior to ovulation.

30
Q

How are vets involved in the timing of mating?

A
  • Scanning of mares

- Scanning of follicles

31
Q

How can scanning mares help determine mating times

A

Detect whether the mare is in oestrus or not.
If in oestrus – scan again 24-48 hours later
If not – give PG and scan again when starts to come into oestrus (3-5 days)

32
Q

A mare in oestrus will have what gross and scanned features?

A
  • Dominant follicle on one ovary
  • Uterine oedema
  • Soft oedematous cervix
  • Behavioural signs of oestrus
33
Q

Describe scanning of follicles at different points of oestrus

A

Numerous follicles present -> dominant follicle developing -> dominant follicle softening and “pointing”- ovulation imminent -> Ovulated: leaving corpus haemorrhagicum

34
Q

Describe how uterine oedema changes during the cycle and how this will show on a scan

A

The endometrium becomes increasingly oedematous during oestrus

  • Dioestrus: no oedema
  • Oestrus: oedema forming
  • Oestrus: Cartwheel oedema
  • Oedema decreases in the twenty four hours before ovulation
35
Q

What size is the follicle at ovulation?

A

> 35mm

36
Q

Which hormone can be used to force ovulation?

A

Human chorionic gonadotropin

37
Q

Describe post mating scanning

A

Scan 12- 24 hours after mating to:-

  • See if mare has ovulated (if not -mate again?)
  • Check only one ovulation (twins)
  • Check for fluid in uterine lumen = post mating endometritis and treat accordingly
38
Q

What is the most common mating problem in mares?

A

Perineal conformation

39
Q

Prevention of bacterial entry to the womb is carried out by which three mechanisms?

A
  • Vulval seal
  • Vestibular seal
  • Cervical competence
40
Q

What happens if there is failure of the vulval and vestibular seal?

A

Allows pneumovagina (which in turn predisposes to urovagina) leading to cervicitis and bacterial contamination of the uterus.

41
Q

What are the consequences of uterine contamination?

A

Leads to endometritis which will lead to failure of implantation of a conceptus

42
Q

How is perineal conformation linked to uterine infection?

A

Poor perineal conformation prevents these seals forming -> uterine contamination

43
Q

How can perineal conformation be corrected?

A

Caslick’s vulvoplasty

  • simple surgery carried out under LA
  • needs to be opened up for foaling
44
Q

What are some ovarian problems in mares?

A
  • Persistent Corpus Luteum: no oestrus
  • Anovulatory follicles: cause prolonged oestrus, follicle increases in size to 10cm but never ovulates
  • Granulosa cell tumour
45
Q

How can you treat a persistent CL?

A

Give prostaglandins

46
Q

How are granulosa cell tumours diagnosed in mares?

A

Diagnose by scan and blood test for Anti-Mullerian Hormone

47
Q

What are the affects of endometritis on conception?

A

Endometrial inflammation Does not affect conception but will affect implantation and the inflammatory prostaglandins released may hasten luteolysis

48
Q

Name the three types of endometritis

A
  • Chronic infectious metritis
  • Free fluid in lumen
  • Mating induced endometritis
49
Q

What are the causes/agents of chronic infectious endometritis?

A
  • Contamination of reproductive tract due to poor perineal conformation
  • Reduced uterine immune defences
  • Strep. zooepidemicus, E.coli, Pseudomonas or Klebsiella, occasionally yeast/fungi
50
Q

Describe Free-fluid in lumen endometritis

A
  • As a result of uterine oedema during oestrus
  • Maybe sterile initially but good culture medium for bacteria
  • May be inflammatory in its own right
51
Q

Describe mating induced endometritis

A
  • Mating contaminates reproductive tract with flora on stallions penis
  • Semen is inflammatory in itself
  • Transient inflammation is normal after mating/foaling/vaginal exam
  • Should be cleared up within 12 hours
52
Q

Describe how to investigate endometritis

A

Scan – especially post service. Persistent fluid or fluid > 1-2cm in depth needs treating
2. Uterine swab and smear
for culture
- Smear for cytology useful
- Guarded swabs or via a vaginal speculum
3. Endometrial biopsy for histopathy, very useful

53
Q

How is endometritis treated?

A
  1. Uterine lavage – using volumes of saline
  2. Oxytocin – repeated doses (10-25 iu) every few hours
  3. Intrauterine antibiotics – eg 1g ceftiofur in 20ml water
  4. Use of A.I. to minimise contamination
54
Q

Describe the process of chronic degenerative endometrial disease

A

A progressive degeneration of endometrium and its replacement by fibrotic tissue

55
Q

What is chronic degenerative endometrial disease a major cause of?

A

Age related infertility

Begins about 11-12 years, by 17 years may have progressed to severe stage

56
Q

Describe the steps of pre-breeding disease clearance

A

Often a clitoral swab for CEM
Blood sample for Equine Viral Arteritis also often asked for- serology
Strangles serology also being asked for by an increasing number of studs

Y3 MOD Reproductive (11 decks)

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