Equine Reproduction Flashcards
Lectures 1-4
Overview
- mares cycle regularly through breeding season (controlled by photoperiod)
- can manipulate this with their environment in some cases to cycle over the winter - idea is to get the foals born at right time with food available
- foals should be born in spring/summer optimally
- Arbitrary artifical birth date depending stimulated by thoroughbreds depending on hemispheres. (Jan 1 in North, Aug 1 in southern) - try to manipulate the mares forward to get them closer to their actual birth date
- age type racing and sales: if you have a foal that was born in August it is going to look better for sales when it is a yearling than if it was born in July
- for thoroughbreds –> get as close to beginning of season as possible
- Sports horses: depends on how it fits into that schedule and management
- conception rates will be lower at a younger age
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Mare Reproductive Anatomy
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- 3 gateways to the mares tract: perineum, transverse fold (end of the vestibule)- the vaginal vault and then the cervix
- 3 layers of protection
- means there are 3 stops for bugs
Mare Anatomy
(Ovary)
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- mares ovaries are quite responsive to the season
- will be rather small if there is no activity (walnut) - anoestrus in the winter
- picture: small anoestal ovary and then larger developing ovary with follicles - follicles get stimulated to be active (often feel like a bunch of grapes when actively ovulating)
- All mares will be ovulating through an ovarian fossa - this is important!! - rather than rupturing in various places, it is always going to rupture in the same place - important in gamete harvesting as well
- Follicles: you will be able to be able to feel the little bubbles
- After ovulation: CL formed and then in horses a corpus hemorrhagica is formed
- all held together by suspensory ligaments that vary on length depending on the mare!
Maiden mares that have never had the pull of pregnancy - shorter and ovaries sit just ahead of tuber coxae - mares with lots of babies - quite a lot of stretch, ovaries can be anywhere from midline to quite low (quite a bit of variability)
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Mare Anatomy
(Uterus)
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- long horns and a reasonsably short body
- T or Y: important for the implantation of the embryo and harbor for disease
- endometrium is important for implantation of the embryo as well as the placenta, it is also another potential site for disease!
- broad ligament can be a spot for hemorrhage during foaling difficulties - important to identify
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Mare Anatomy
(Cervix)
- mares: about 10cm
- in ponies it is about 4cm
- has a definitive os cervix
- anoestral cervix has tone to it, but no color (closed opening)
- oestral cervix: rosebud appearance and becomes a wilted rosebud appearance as it gets closer to ovulation (melting into floor of vagina) - good way to judge if the mare is in season
- needs to be soft to be receptive to the stallion!
- Dioestral: after ovulation, more tone to it and then under the influence of the pregnancy it is a tight fist
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Mare Anatomy:
Perineum
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- First stop to prevent infection
- also one of the first spots for veterinarian intervention
- clitoris is where you get a lot of harboring of disease
- need to look at these areas for pre-breeding swabs
- remember clitoral sinus and clitoral fossa
- remember this orientation and with multiparous mares this becomes altered and then you run into issues with infections and such
- not a nice straight confomation
- h= bladder
- there is space in the abdomen which makes sense so if you have a big foal developing it will drop down and not squish the bladder
Breeding Season and Oestrus Cycle
- Throroughbreds: earlier in the year
- polar ponies: later in the year (when they are finished playing and don’t have to be in sales/racetrack)
- sports horses: usually in the middle of the year
- Generally April, May, June is peak time
- after that- no chance really of getting them pregnant and then once the clocks change there really is no go
- want to increase day length if we can as it has a lot of effect on their cycle
- bad weather can really impact the way the mares function! - really want to push the daylength to about 16 hours
- can do this with artificial light - enough to read a paper
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Influences on Breeding Season and Oestrus Cycle
- stimulate the hormones from the brain that we need to move forward
- green grass effect: if you have grass, that is good for the mares and then there is a response to try and enhance reporduction at that point
- plane of nutrition increase in empty mares will aid conception rates (like FA’s)
- daylength is still key!
- but weight will have an effect!
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Hormonal Pathway
- melatonin in the spring time drops and that stimualtes the GnRH release in the hypothalamus (which we can alter sometimes)
- which then stimulates the anterior pituitary and so on
- we know that we can stimulate the GnRH release at times and increase daylight
- nut ovary –> grape structure producing oestrogens
- get behavior changes and changes in the tract
- need feedback of oestrogen to promote follicle maturation by the relasse of LH!
- without LH surge, don’t get anything but smoldering ovaries that are producing enough oestrogen to get changes in behavior but not enough to get proper maturation of the follicle or ovulation
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- We need this feedback of estrogen to have that necessary LH surge
Transitional Period
- time just before the peak breeding season after winter
- this is the part we are trying to move forward in terms of mares cycling for thoroughbreds
- variable, depends on hemisphere!
- Want to kick ovaries into action to get early oestrus cycle
- mares will show signs but they won’t have enough oestrogen to have LH surge
- We know we can manipulate the light - need to be able to read newspaper in the stable
- Dopamine anatognist can be applied to fire ovaries out of the transition stage
- in the US: use progesterone/estradiol to try and prime up the whole HPA axis –> don’y have this in the UK and EU
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Oestrus Cycle
- once we are out of the transition phase we are into a true oestrus cycle
- oestrus ballpark is about 3 weeks
- really only a few days where they will actually be able to stand
- There are only a few days when they are ready to stand (then you are talking about AI or naturally breeding)
- PGF2a release from the uterus kicks off the next cycle
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Oestrus Cycle: Hormones
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Oestrus or Follicular Phase
- follicular development will lead to oestrogen release
- mares are then starting to show signs they are ready to be mated
- uterus under the influence of oestrogen will become oedemetous (wet woolen sock) –> like a heavy doughy tube
- wink, posture and pee
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- a bunch of small follicles (1-2 cm in diameter) - all under the influence of FSH
- then start to get one big decent sized dominant follicles and then shut the rest up
- occassionaly end up with 2 dominant follicles - but if more than one gerts ovulated off then there is the twin potential
- If we have more than one dominant follicle, there is potential for twins which is not ideal for horse repro
- follicle goes towards ovulation fossa and then shoots egg into fallopian tube - will see a “collapse down”
- will see hypoechoic activity in the middle of the follicle
Oestrus: Follicular Development
-want to see an increase to the size of the follicle (why we measure in cm) to where we can possibly manipualte with drugs
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Oestrus: Ovulation
- some mares will variably want to ovulate at a 3.6 cm or 5cm follicle which makes it hard to mate with a stallion
- work with certain mares and know what their size pattern is
- measuring follicles does help, but is not the sole way we tell oestrus
- Once an ovulation has occurred (shown as flattenting on other slide) , we have a corpus haemorrhagica (baiscally blood into the space) that forms and then become CL to produce progesterone
- the presence of a corpus hemorrhagica is a good sign that she has ovulated already
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Oestrus: Ovulation Hormones
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- follicle release vs. CL and hemorrhagica formation
Oestrus: Uterus
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- again “wet woolen sock”
cartwheel appearance on US is what you want to be looking for!
black fluid - oedema –> remember : Oedematous uterus
closer to standing oestrus - you will possibly see some fluid accumulation in the middle (should be less than 2cm!)
If more than 2 cm —> excessive fluid
usually fluid reduces just before ovulation (can look for the decrease)
Dioestrus or Luteal Phase
- usually a window of 24-48 hours before the cervix closes (3-4 days aft
- they will NOT be having the presence of the stallion anymore
- we can also manipulate the lysis of the CL –> IMPORTANT
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Manipulation of Oestrus Cycle
(transitional phase)
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Manipulation of Oestrus Cycle
(dioestrus)
- Can give PGF2a to get rid of that CL
- but the CL must be ripe enough to be lysed by the PGF2a (5 - 7days)
- When you know you have your corpus hemorrhagica that is day 1
- in attempts to help bring these mares forward by a week or two
- 2 types of PGF2a you can give (IM ONLY)
- this is a powerful hormone - so they need to know what they are doing and know how to give properly
- people need to be sure they know how to give an IM injection!
- it can really affect horses and people as well!
- You will get sick if you accidentally jab yourself with this
- never to be used if anyone thinks they are pregnant!
- can also even cause asthma in people by inhalation
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Manipulation of Oestrus Cycle
(Dioestrus- Prolonging or support of dioestrus)
- we know now that we can shorten the cycle
- NOW, how do we lengthen it?
- oral prgesterone that needs to be given everyday
- dont pour into feed and mix in with their hands!
- progesterone can have adverse effects on people as well
- It IS legal for an FEI (equestrian) horse
- if you give it to a horse you think is competing though, you need to look back at the regulations
- Depo provera (not licensed for horses) can only be used with good reasoning
- Regumate is a better oral and licensed oral preparation to use
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Manipulation of Oestrus Cycle
(Inducing Ovulation)- HCG
- mimics LH surge
- want surge to make follicles mature and ovulate
- mix up solution and give IM or IV
- nice water base- and mix it up with solution
- quite handy
- not good for older mares as they tend to not respond well and indications that they may get used to it with multiple applications - won’t have desired response
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Manipulation of Oestrus Cycle
(Inducing Ovulation)- GnRH agonists
- hopes to promote the stimulation for the ovulation
- most the time will ovulate in a 48 hour gap
- we will drive the follicle, but won’t reduce fertility
- chorulon will ovulate the follicle as long as it is 3cm, but won’t necessarily mature it to the same rate
- Ovuplant will drive it to mature and ovulate and you are not going to get a reduction in fertility
- chorulon may be good for frozen semen bc it means you are making the cycle shorter
- ovuplant for throughbreds so we have bigger window to get them to the stallion and the studs
- ovuplant is a Subcutaneous implant you put in with a big syringe, so you can’t short cycle them off - if you want to bring them back, won’t respond to PGF2a
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Reproductive Abnormalities: Ovary
- Anovulatory follicle can be 6-7cm or even get up to 10 cm
- see in the shoulder seasons or the prolonged transitional season
- these are not the same as a follicular or ovarian cyst! it is a follicle that just hasn’t had the surge to push it
- sometimes called “autumn follicles” as the mares don’t think they need to breed anymore - can be a massive pain!
- Just a follicle that hasn’t had the urge to push it, will over time eventually rupture
- they may be painful - be careful when examining
- The horses may be misbehaving due to improper hormones
- Granulosa Theca Cell Tumor: not to be confused with your corpus hemorrhagica
- get honey comb type appearances
- some of these could get massive before we caught them with scanning (basketball size) - would then need to be SX removed and they would have to be on their back
- probelm is that they produce inhibin - inhibin is a feedback loop so it will suppress the oestrogen and make them have more stallion like behavior (wont cycle properly and will end up surpessing the other ovary)
- will end up feeling one that is repressed by the inhibin and one that is not
- can now measure AM hormone and use US to make Dx
- not all GTC’s will produce the same amount of hormone across the board
- can run inhibin to get final Dx
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Reproductive Abnormalities: Uterus
(endometritis)
- we know it gets oedematous and is also the touching point for conceptus/fetus and placenta
- because it is vascular, we end up with bugs there
- endometritis is a common thing among mares
- ALL SEMEN IS DIRTY- including chilled or frozen semen
- will always cause some degree of metritis post breeding and that is part of the repair process
- as mares get older they lose their immunity in the endometrium - struggle to get more control and can end up with scarring and a resulting persistent metritis
- when we are breeding, we want to manage the post breeding metritis as we dont want bugs to set up shop in there
- then we have post-foaling metritis from parturition
- conformation of the mare is also a part of metritis (change in shape of perineum)
- the ones we need to be aware of as a vet as it is our responsibility is Contagious endometritis (CEM), Kebsiella, Pseudomonas
- this can extend our oestrus period as the body is trying to drive it out –> mare may be in season and trying to stand for 10,12, 14 days (rather than normal 5-7) and that is a problem! - not actually in season
- or if she comes back into cycle too early!
- Infection is goign to keep that cervix open as it want to clear something out –> will drive her to continue showing oestrogenic signs
- can have persisitent fungal ones as well! (2 ways of treating these)
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Reproductive Abnormalities: Uterus
(post breeding endometritis: Treatment)
- need to get everything out, lavage is the best option
- (just need to wait 6 hours post ovualtion and service with insemination or covering)
- Not every mare needs a lavage, but a lot of them it helps
- want phosphate buffered saline to make sure it is not too corosive as it is a luminal env’t
- should run a culture and senisitivity with it as well so we can pick the AB
- The one we use more often is Ceftiofur - cephalosporin (broad spectrum, doesnt seem to harm uterine env’t)
- can even use vinegar for fungal infection
- myometrium (muscular layer) - want that to contract to get fluid out –> oxytocin (also allows for milk letdown!)
- Corticosteroids: something we are starting to use after ovulation to reduce inflammation
- probably only other systemic drug other than the oxytocin to try and reduce the effects of the metritis
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Reproductive Abnormalitites: Uterus
(chronic endometritis/endometriosis)
- can diagnose by biopsy! -can tell you what kind ofpregnancy rates you are going to have
if we want to look at the actual cells - do a swab - sometimes use corrosive agents to try and get the body to shed the endometrium to promote a new healthy layer for the conceptus
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Endometriosis- Kenney Scale
- healthy uterus at top and then decreases towards bottom
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Reproductive Abnormalities: Uterus
(3)
- things IN the uterus that may be going wrong
- top right: can tell it is a of dioestrus and those are endometrial cysts–> can easily be confused for pregnancy!
- or you can have a cyst and pregnancy and confuse for twins
- cysts will vary slightly over the breeding season but if you get a good measurement, then you can usually catch them (map your size)
- middle: foreign body in the uterus (uterine marble which we use to stop them from cycling to manipulate pregnancy) - often get left there! –> leave an acoustic shadow (can know if is a FB)
- can even find broken off swab tips
- uterine adhesions
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Preliminary Considerations for breeding a mare
- what they are going to do and when
- thoroughbreds breed for a defined birth date
- depending on function of horse
- Thoroughbreds are always natural breeding (cover)
- remind them that they will INDEED need to be prepared to have a foal in 11 months time
- gestation: 11-12 months
- polo ponies towards the end of the season - not as worried about embryos and such when they are for sport seasons
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Breeding Soundness Exam
- has she had a foal before?
- have they had pelvic fracture or colic Sx - not a good breeding candidiate! - may be good for donate embryo though?
- neither is a young filly, baby with a young horse pelvis - if you are trying to breed them, may run into dytocia risk
- need to check soundness of the horse and that includes orthopedic stuff! - can they actually carry the foal?? (70-80 kg of foal)
- no point in breeding a mare that is struggling to manage its own body weight
- could lead to laminitis or other major complications
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Code of Practice- Obligations
(Notifiable/Non-notifiable)
- we DO have a duty to the country especially in regards to diseases
- as vets we are responsible for notifiable diseases
- EIA: is not in the UK (exotic), any of the horses that have it (or positive serology) will get euthanased, should not be coming into the country, but it IS in europe (can periodically get horses testing positive)
- if it is a domestic horse, likely hasnt been exposed - maybe still good to check
- thoroughbred - still HAS to be tested for it by regulation
- EVA: also a notifiable disease! STD- from the stallion
- CEM: one of the areaswe want to be swabbing for. can sometimes show up as random positives (low levels of posiitves in the country- possible from fomites from teasing stallions) , is notifiable!
there is a testing regime for some non-notifiable diseases and they are just as important!
- still need to have clear Klebsiella and pseudomonas
- these two along with CEM are tested on the same swabs
- Strangles- a lot of studs will ask for vaccination clearance before even allowing horses on
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