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DVM3: Horses - Reproduction > Equine breeding management > Flashcards

Equine breeding management Flashcards

1
Q

What 4 techniques are available to manage seasonal anoestrus?

A

Artificial/supplemental light
GnRH agonists
Progestagens
Dopamine antagonists

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2
Q

What are the 3 main reasons for manipulating the equine oestrous cycle?

A
  1. Enables breeding at a set time
  2. Allows breeding a group at a set time
  3. Enables delay of breeding to a set time
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3
Q

What is the goal of providing artificial/supplemental light to a mare?

A

To indue oestrus earlier in season

  • At Sep 1 (start of breeding season), only 25% of mares are cycling regularly
  • Other 75% are in transitional oestrus = follicular waves w/o any follicle reaching dominance > partial signs of oestrus w/o OV
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4
Q

What are the practical aspects of providing artificial light?

A

Supply in stables or yards
Min 100 lux (able to read a newspaper)
16hrs light/day for 6-8wks
- additional light is more effective if supplied at end of day
Sufficient light to illuminate whole area - no dark corners

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5
Q

What techniques/drugs are available to suppress oestrus?

A 
Progestagens (Regumate)
GnRH vaccines (Equity)
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6
Q

How is progesterone used to induce OV in mares in transitional oestrus?

A

Requires follicle = 20-25mm on one ovary

  • Regumate (progestogen; 10 mL/d for 10d)
  • PG on d10 (luteolysis if OV already occurred)
  • if effective = oestrus signs w/in 3 days > OV 5-7d later
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7
Q

Why would synchronisation of oestrus be a useful tool?

A

Planned matings
AI + embryo transfer
Silent oestrus
Persisten CLs/anovulatory haemorrhagic follicles

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8
Q

What is the normal physiological role of PGF2a in the oestrous cycle in mares?

A

PGF2a = luteolysin (TF ends luteal phase)

  • released by uterus when no pregnancy recognition occurs
  • no counter-current utero-ovarian v. in mares (as in ruminants) > TF PGF2a enters systemic circulation before reaching the ovary to induce luteolysis
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9
Q

What is PGF2a tx used for in equine repro?

A

To short cycle mares (in dioestrus) –> synch protocol

- luteolysis > decreased P4 > increased FSH/LH > follicular growth + dominance

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10
Q

What conditions must be met for a PGF2a injection to be effective in causing luteolysis?

A

CL > 5 days old

i.e. >5d post-OV

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11
Q

When will a heat/ovulation occur post-PGF2a injection? What factors cause variation in this + why?

A

Oestrus (heat) = 3d post-injection
OV = 4-7d later

Variation dt stage of follicular wave at point of PGF2a admin
- Dom follicle near end of growth > earlier OV

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12
Q

What are some reasons a PGF2a injection may not induce luteolysis?

A

CL < 5d old
Mare not in dioestrus (i.e. anoestrus, silent oestrus, transitional oestrus, > 35d pregnant)
Granulose cell tumour

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13
Q

What side effects are common with PGF2a injections?

A

Sweating
Discomfort
Colic (occasional)

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14
Q

What PGF2a dose is given to mares to induce luteolysis?

A

Single dose of 5mg

- 5x less than ruminant dose!

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15
Q

Combined oestrogen-progesterone treatment - protocol

A

P4 (150 mg IM) + E2 (10mg IM) for 10 days

> PGF2a on day 10

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16
Q

Rationale behind combined E2-P4 tx

A

Oestrus synchronisation:

  • P4 = simulates dioestrus
  • E2 (low dose) = suppresses FSH TF suppresses follicle growth
  • PGF2a = luteolysis, but all mares start with a new follicular wave
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17
Q

What result will combined E2/P4 tx have on A) mares in heat, B) mares in early-mid dioestrus, C) mares in late dioestrus

A

A - OV in first few days of tx so new CL is > 5d old (TF receptive at d10 PGF2a

B - mares have responsive CL

C - mares will have undergone spontaneous luteolysis

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18
Q

3 methods of synchronising mares oestrous cycles

A

PGF2a (single dose)
Combined E2/P4 treatment
Regumate (oral progestogen)

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19
Q

What methods (drugs) are available to induce ovulation during oestrus in mares? Why would this be done?

A 
Human chorionic gonadotropin (hCG)
GnRH analogues (Ovuplant)

Reasons: variable interval from onset of oestrus > OV
- accurate timing of OV for AI/natural breeding, part of synch program, interruption of transitional oestrus)

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20
Q

How does hCG work to induce OV?
Dosage of hCG
Follicular conditions to admin
When do mares ovulate?

A

LH-like effect > selection of a dominant follicle + OV
Dose = 1500-300 IU
Dominant follicle = 35-40mm + some oedema
Majority (85%) OV 36-42hrs post-admin

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21
Q

How does GnRH (deslorelin) work to induce OV?
Dosage of GnRH
Follicular conditions to admin
When do mares ovulate?

A

Slow release GnRH > endogenous FSH/LH prod’n > OV
Dose = 2.2mg (in implant)
Dominant follicle > 30mm + uterine oedema
Majority (80%) OV 42-48hrs post-implantation

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22
Q

Where is the GnRH/deslorelin implant placed?

What happens after OV?

A

Placement = submucosal in labia

Remove implant to prevent down-reg of GnRH-R (+ delayed subsequent OV)

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23
Q

Compare adv. + disadv. of hCG/GnRH for OV-induction

A 
GnRH = \$\$$ 
hCG = earlier OV (36--42hrs c.f. 42-48hrs)
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24
Q

Compare adv. + disadv. of PGF2a/combined E2-P4 tx/oral Regumate to synchronise mare’s oestrus cycles

A

PGF2a = cheap, rapid, single dose > good for single mares
- Disadv. = side effects, not useful for groups

E2-P4 = very good synch in a group of mares, can be initiated at any stage, applicable to mares in transition
- Disadv. = $$, takes time (20d), not registered)

Reg = oral admin, applicable to mares in transition
- Disadv = poorer synch, $$$

25
Q

When should OV be induced (i.e. timing) for mating/AI?

A

Base on follicular size - wait for 35-40mm follicle
> OV-induction (hCG/GnRH) 24hrs before service/AI
> OV w/in 48hrs of admin = w/in 12-24hrs of service

If using fresh semen/natural mating, sperm lasts longer in tract TF can serve further before OV

26
Q

What criteria are useful in assessing timing of service?

A 
Follicle size (based on rectal palp/US) > can induce OV reliably
Cervical tone (based on vaginal exam) = relaxation as OV approaches > closes after OV
Mare receptivity to teaser stallion
27
Q

Protocol for teasing of mares

A

Daily teasing from 3d postpartum to 60d pregnant

  • use a teasing chute/wall
  • introduce teaser at head then turn mare to give teaser access to perineum
28
Q

How many mares will a TB stallion mate each day + in a season throughout the breeding period?

A

2-3 mares/day for 6-7 days/wk from Sep 1st - Dec 31st

= 350 mares/season

29
Q

Advantages of AI over natural service

A

More mares able to be bred to a single stallion - division of an ejaculate into ≥1 dose
Don’t need mare/stallion in same place
Limits tm of STIs - semen extenders contain ABs
Limits injuries during mating (to mare/stallion/handlers)
Breeding possible with incompatible horses (size, temperament, etc.)
Minimum contamination breeding techniques
Quality control/monitoring of stallion semen quality

30
Q

What is the AI dose of semen considered adequate for conception?

A

≥200 million normal progressively motile sperm

  • measured by sperm count + motility assessment
  • 10-25 mL insemination V
  • can go lower than 200m but with variable efficacy
31
Q

Method of semen collection from stallions

A

Artificial vaginas - must be clean + non-spermicidal

32
Q

Semen handling post-collection

A

Collect
> measure gel-free V, motility, concentration, morphology
> Warm extender added (37 degC, 1:2-1:4 ratio = 25-50million sperm/mL)
> use w/in 3hrs at room T

33
Q

When is AI performed with fresh extended semen?

A

1-3d before OV (up to 8h post-OV)

34
Q

Why is AI with raw semen not advised?

A

Transmission of bacteria in the ejaculate to the mare

35
Q

What is the advantage/best use of chilled (non-frozen) semen?
How long can chilled extended semen be used for?

A

Allows shipping of semen to distant locations

Use w/in ≤72hrs of collection (may be less in some stallions)

36
Q

Efficacy of AI with chilled extended semen

A

Variable by stallion/farm management practice

- doesn’t work for all stallions

37
Q

How is semen cooled (rate/target T)?

A

Cool to 5 degC at rate of 1 degC/3min

38
Q

Protocol for using frozen semen

A

Daily US until 30mm dominant follicle (= d1)
> GnRH/hCG tx on evening of d1 (t=0hr)
> AI t=42hrs (ideally 12hr before – 6hr after OV)

Requires scanning @

  • t=24hr > ensure no early spontaneous OV
  • t=36hr > ensure she hasn’t OV already
  • t=48hr > ensure OV occurred
39
Q

What is the foal heat?

When does it occur?

A

1st heat after foaling > ends w 1st OV post=partum

  • onset = 6-9d post-foaling
  • OV = w/in 18d post-foaling
40
Q

Why is conception on the foal heat desirable?

A

Get mare pregnant earlier in the season = gains 3 weeks growth for racing

41
Q

Are there any reasons not to breed a mare on her foal heat?

A

Complicated birth - dystocia, RFM etc.
OV before d10 post-partum = high EEL rate

TF its a trade off between getting mare in foal early + having a good pregnancy outcome

42
Q

What 3 events must occur in the uterus post-partum for a mare to be ready for a new pregnancy?
What implications do these factors have on management of the mare?

A
  1. Uterine involution
  2. Shedding of uterine bacteria (i.e. no endometritis)
  3. Resumption of regular cyclic ovarian activity

TF shouldn’t induce OV in foal heat - may cause OV before these 3 events have occurred

43
Q

What action should be taken if a mare ovulates within d10 post-partum, when the intention was to breed her on the foal heat?

A

OV < d10 = high EEL rate

–> short cycling the mare (PG shot) will cause 2nd OV to be a week earlier than if she was left untx’d

44
Q

Which methods of mating/AI are useful for breeding on foal heat? Which aren’t?

A

Yes = natural or fresh semen
- maybe chilled extended semen w variable results

No = frozen semen (requires OV-induction dt short residence time in female RT)

45
Q

What is the goal of the minimal contamination technique (MCT) for AI of mares?

A

To minimise the chance of endometritis (endometrial infections)

46
Q

What are the indications for using the MCT?

A 
Stallions known to shed bacterial pathogens
Susceptible mares (Hx of recurrent endometritis)
47
Q

How should semen be handled if intended to be used by MCT?

A

Dilute w extender ± centrifugation

  • 1:4 ratio semen:extender
  • [sperm] = 25-50million/mL
48
Q

When should AI occur when using the MCT?

A

As long before OV as possible (ideally 48hrs)

- chilled/extended semen used the day after ordering

49
Q

Plan/protocol for using the MCT to AI a mare

A

Order semen (d1)
AI next day (d2)
- flush any uterine fluid out w saline beforehand
- give OXT at end of each flush + 4hr post-AI
Manually dilate the cervix following AI
Induce OV (GnRH ag) post-AI > OV w/in 48hrs
Check if OV following day (d3)

50
Q

When using the MCT for AI, what actions should be taken if uterine fluid is seen on US before AI?

A

Flush uterine fluid w saline (until return fluid is clear)

  • immediately prior to breeding
  • continue until 2-3d post-OV if necessary
  • systemic AB tx (TMS) until 3d post-OV
51
Q

Why must the cervix be manually dilated following AI?

A

Mimics the stallions penis - the glans penis dilates cervix + deposits semen directly into the uterus

52
Q

What tx for pneumovagina following AI using MCT?

A

Temporary caslick - daily + permanently after end of tx

53
Q

When to conduct + what to look for in a post-AI US preg exam?

A

d14 post-OV

Look for:

  • a structure which looks like a small follicle located in the uterus
  • examine the CL integrity
  • any uterine oedema (should be none - indicates inflammation)
54
Q

Success rate when using frozen semen for AI

A

30-35% per cycle – highly dependent on individual stallions semen quality + breeding health of mare

  • fertile stallions semen may not freeze well
  • 5-6yo mare c.f. 18yo mare
55
Q

When should a frozen semen approach be abandoned in favour of fresh/chilled semen?

A

Poor mare breeding health

No conception by 3rd cycle of AI w frozen semen

56
Q

When using frozen semen for AI, if mare hasn’t OV at scan at 48hrs into protocol (OV check), what actions to take?

A

Owner’s decision:
1 - skip that cycle
2 - scan mare every 6hr to AI again when OV is detected (but must wait ≥18hrs after 1st AI to give 2nd AI dt inflammatory uterine rxn)

57
Q

How might uterine cysts cause pregancy loss/poor pregnancy outcomes?

A

Block conceptus contacting all areas of uterus = no maternal recognition of pregnancy

58
Q

How are uterine cysts tx’s?

A

Progestagens from 1wk post-OV

- maintains high P4 at luteolysis

DVM3: Horses - Reproduction (7 decks)

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