Equine breeding management Flashcards
What 4 techniques are available to manage seasonal anoestrus?
Artificial/supplemental light
GnRH agonists
Progestagens
Dopamine antagonists
What are the 3 main reasons for manipulating the equine oestrous cycle?
- Enables breeding at a set time
- Allows breeding a group at a set time
- Enables delay of breeding to a set time
What is the goal of providing artificial/supplemental light to a mare?
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
What are the practical aspects of providing artificial light?
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
What techniques/drugs are available to suppress oestrus?
Progestagens (Regumate) GnRH vaccines (Equity)
How is progesterone used to induce OV in mares in transitional oestrus?
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
Why would synchronisation of oestrus be a useful tool?
Planned matings
AI + embryo transfer
Silent oestrus
Persisten CLs/anovulatory haemorrhagic follicles
What is the normal physiological role of PGF2a in the oestrous cycle in mares?
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
What is PGF2a tx used for in equine repro?
To short cycle mares (in dioestrus) –> synch protocol
- luteolysis > decreased P4 > increased FSH/LH > follicular growth + dominance
What conditions must be met for a PGF2a injection to be effective in causing luteolysis?
CL > 5 days old
i.e. >5d post-OV
When will a heat/ovulation occur post-PGF2a injection? What factors cause variation in this + why?
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
What are some reasons a PGF2a injection may not induce luteolysis?
CL < 5d old
Mare not in dioestrus (i.e. anoestrus, silent oestrus, transitional oestrus, > 35d pregnant)
Granulose cell tumour
What side effects are common with PGF2a injections?
Sweating
Discomfort
Colic (occasional)
What PGF2a dose is given to mares to induce luteolysis?
Single dose of 5mg
- 5x less than ruminant dose!
Combined oestrogen-progesterone treatment - protocol
P4 (150 mg IM) + E2 (10mg IM) for 10 days
> PGF2a on day 10
Rationale behind combined E2-P4 tx
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
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 - 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
3 methods of synchronising mares oestrous cycles
PGF2a (single dose)
Combined E2/P4 treatment
Regumate (oral progestogen)
What methods (drugs) are available to induce ovulation during oestrus in mares? Why would this be done?
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)
How does hCG work to induce OV?
Dosage of hCG
Follicular conditions to admin
When do mares ovulate?
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
How does GnRH (deslorelin) work to induce OV?
Dosage of GnRH
Follicular conditions to admin
When do mares ovulate?
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
Where is the GnRH/deslorelin implant placed?
What happens after OV?
Placement = submucosal in labia
Remove implant to prevent down-reg of GnRH-R (+ delayed subsequent OV)
Compare adv. + disadv. of hCG/GnRH for OV-induction
GnRH = \$\$$ hCG = earlier OV (36--42hrs c.f. 42-48hrs)
Compare adv. + disadv. of PGF2a/combined E2-P4 tx/oral Regumate to synchronise mare’s oestrus cycles
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. = $$, takes time (20d), not registered)
Reg = oral admin, applicable to mares in transition
- Disadv = poorer synch, $$$
When should OV be induced (i.e. timing) for mating/AI?
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
What criteria are useful in assessing timing of service?
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
Protocol for teasing of mares
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
How many mares will a TB stallion mate each day + in a season throughout the breeding period?
2-3 mares/day for 6-7 days/wk from Sep 1st - Dec 31st
= 350 mares/season
Advantages of AI over natural service
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
What is the AI dose of semen considered adequate for conception?
≥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
Method of semen collection from stallions
Artificial vaginas - must be clean + non-spermicidal
Semen handling post-collection
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
When is AI performed with fresh extended semen?
1-3d before OV (up to 8h post-OV)
Why is AI with raw semen not advised?
Transmission of bacteria in the ejaculate to the mare
What is the advantage/best use of chilled (non-frozen) semen?
How long can chilled extended semen be used for?
Allows shipping of semen to distant locations
Use w/in ≤72hrs of collection (may be less in some stallions)
Efficacy of AI with chilled extended semen
Variable by stallion/farm management practice
- doesn’t work for all stallions
How is semen cooled (rate/target T)?
Cool to 5 degC at rate of 1 degC/3min
Protocol for using frozen semen
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
What is the foal heat?
When does it occur?
1st heat after foaling > ends w 1st OV post=partum
- onset = 6-9d post-foaling
- OV = w/in 18d post-foaling
Why is conception on the foal heat desirable?
Get mare pregnant earlier in the season = gains 3 weeks growth for racing
Are there any reasons not to breed a mare on her foal heat?
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
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?
- Uterine involution
- Shedding of uterine bacteria (i.e. no endometritis)
- Resumption of regular cyclic ovarian activity
TF shouldn’t induce OV in foal heat - may cause OV before these 3 events have occurred
What action should be taken if a mare ovulates within d10 post-partum, when the intention was to breed her on the foal heat?
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
Which methods of mating/AI are useful for breeding on foal heat? Which aren’t?
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)
What is the goal of the minimal contamination technique (MCT) for AI of mares?
To minimise the chance of endometritis (endometrial infections)
What are the indications for using the MCT?
Stallions known to shed bacterial pathogens Susceptible mares (Hx of recurrent endometritis)
How should semen be handled if intended to be used by MCT?
Dilute w extender ± centrifugation
- 1:4 ratio semen:extender
- [sperm] = 25-50million/mL
When should AI occur when using the MCT?
As long before OV as possible (ideally 48hrs)
- chilled/extended semen used the day after ordering
Plan/protocol for using the MCT to AI a mare
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)
When using the MCT for AI, what actions should be taken if uterine fluid is seen on US before AI?
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
Why must the cervix be manually dilated following AI?
Mimics the stallions penis - the glans penis dilates cervix + deposits semen directly into the uterus
What tx for pneumovagina following AI using MCT?
Temporary caslick - daily + permanently after end of tx
When to conduct + what to look for in a post-AI US preg exam?
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)
Success rate when using frozen semen for AI
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
When should a frozen semen approach be abandoned in favour of fresh/chilled semen?
Poor mare breeding health
No conception by 3rd cycle of AI w frozen semen
When using frozen semen for AI, if mare hasn’t OV at scan at 48hrs into protocol (OV check), what actions to take?
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)
How might uterine cysts cause pregancy loss/poor pregnancy outcomes?
Block conceptus contacting all areas of uterus = no maternal recognition of pregnancy
How are uterine cysts tx’s?
Progestagens from 1wk post-OV
- maintains high P4 at luteolysis
