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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
How can the photoperiod be used to manipulate oestrus?
- 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
When might oestrus suppression be requested?
For mares whose sexual behaviour makes life difficult for owner
27
Give some examples of behaviours that may lead to owners wanting oestrus suppression of their mares?
- 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
What are the methods for suppressing oestrus in mares?
- 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
How should mating be timed for conception in horses
- 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
How are vets involved in the timing of mating?
- Scanning of mares | - Scanning of follicles
31
How can scanning mares help determine mating times
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
A mare in oestrus will have what gross and scanned features?
- Dominant follicle on one ovary - Uterine oedema - Soft oedematous cervix - Behavioural signs of oestrus
33
Describe scanning of follicles at different points of oestrus
Numerous follicles present -> dominant follicle developing -> dominant follicle softening and “pointing”- ovulation imminent -> Ovulated: leaving corpus haemorrhagicum
34
Describe how uterine oedema changes during the cycle and how this will show on a scan
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
What size is the follicle at ovulation?
>35mm
36
Which hormone can be used to force ovulation?
Human chorionic gonadotropin
37
Describe post mating scanning
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
What is the most common mating problem in mares?
Perineal conformation
39
Prevention of bacterial entry to the womb is carried out by which three mechanisms?
- Vulval seal - Vestibular seal - Cervical competence
40
What happens if there is failure of the vulval and vestibular seal?
Allows pneumovagina (which in turn predisposes to urovagina) leading to cervicitis and bacterial contamination of the uterus.
41
What are the consequences of uterine contamination?
Leads to endometritis which will lead to failure of implantation of a conceptus
42
How is perineal conformation linked to uterine infection?
Poor perineal conformation prevents these seals forming -> uterine contamination
43
How can perineal conformation be corrected?
Caslick's vulvoplasty - simple surgery carried out under LA - needs to be opened up for foaling
44
What are some ovarian problems in mares?
- Persistent Corpus Luteum: no oestrus - Anovulatory follicles: cause prolonged oestrus, follicle increases in size to 10cm but never ovulates - Granulosa cell tumour
45
How can you treat a persistent CL?
Give prostaglandins
46
How are granulosa cell tumours diagnosed in mares?
Diagnose by scan and blood test for Anti-Mullerian Hormone
47
What are the affects of endometritis on conception?
Endometrial inflammation Does not affect conception but will affect implantation and the inflammatory prostaglandins released may hasten luteolysis
48
Name the three types of endometritis
- Chronic infectious metritis - Free fluid in lumen - Mating induced endometritis
49
What are the causes/agents of chronic infectious endometritis?
- Contamination of reproductive tract due to poor perineal conformation - Reduced uterine immune defences - Strep. zooepidemicus, E.coli, Pseudomonas or Klebsiella, occasionally yeast/fungi
50
Describe Free-fluid in lumen endometritis
- 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
Describe mating induced endometritis
- 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
Describe how to investigate endometritis
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
How is endometritis treated?
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
Describe the process of chronic degenerative endometrial disease
A progressive degeneration of endometrium and its replacement by fibrotic tissue
55
What is chronic degenerative endometrial disease a major cause of?
Age related infertility | Begins about 11-12 years, by 17 years may have progressed to severe stage
56
Describe the steps of pre-breeding disease clearance
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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