Equine Anatomy & Physio 2

drhartz's version from 2017-10-20 21:45

Estrus Synch

Question Answer
4 reasons you'd wanna do estrus synch?(1) Fixed time breeding
(2) AI (Fresh-chilled or frozen-thawed)
(3) Stallion availability & management
(4) Embryo transfer (Donor & recipient management)
What big no-no should you know about AI?AI is NOT ALLOWED in thoroughbreds! Must breed via Live Cover
Which 3 types of drugs can you use for doing an estrus synch?(1) Progestogens
(2) Progestogens & estradiol
(3) PGF2α
Why do progestagens work for synchronizing estrus?Mimics the luteal phase ie. Diestrus. So, exogenous progesterone suppresses LH (when you remove this, then they go into estrus all at the same time)
Progestagens are usually given in what medium & what does this mean in terms of admin?P4 in oil (Injxn site Rxns)
If you are using P4 (progestagens) ALONE for estrus synch, how long must you do this for & why?Tx for 14-18d to ensure regression of previous CL
- This is why we often use in combination w/ PGF2α on last day of Tx
Progestagens for estrus synch → when would you expect estrus after end of Tx? Ovulation? (What might change these time guidelines?)Onset of estrus in 3-6 d, ovulation in 8-15 d
However, can get ovulation during Tx... Results in prolonged luteal phase due to exogenous + endogenous P4 (again this is why we give PGF2α at the end of Tx)
What can you do to dec Tx interval w/ progestagens?Can add PGF2α @ end of P4 Tx (removes any CLs that might still be present)
Why would you wanna synch w/ Progesterone & Estradiol?P4 alone won't block FSH & follicular activity... Therefore add Estradiol to program (estradiol inhibits FSH → suppressed follicular activity → NO diestrus ovulations during Tx → improves synchrony)
How long do you Tx w/ progesterone & estradiol, & what route of admin?10d, in oil IM
How long would you wait for ovulation to occur after stopping a progesterone+estradiol Tx regimen?Ovulation in 10-12 d (can incld PGF @ end of Tx to improve synchrony)
WHEN can you start to use PGF2α to estrus synch?CL responsive to PGF2α from D5-12
If you give, PGF2α at the proper time (from D5-12) how long until youd expect estrus. Ovulation?Estrus in 2-4 d
Ovulation in 7-12 d
Natural vs synthetic PGF2α - whats the big whoop? (Names for the synth vs natural)Synthetic (Estrumate) is MUCH more potent, so need WAY less! (horses are super sensitive to PGF to begin w/ as compared to cows, so REALLY need less) (Natural is Lutalyse)
May get variable response to Tx w/ PGF2α...Why? (4 reasons)(1) CL refractory until D5
(2) Spontaneous ovulation >D12
(3) Diestrus ovulation & therefore immature CL
(4) Follicle >/= 3.5mm present @ Tx - may cz ovulation
What are dosages like of natural (Lutalyse) versus synthetic (Estrumate) PGF2α?NATURAL is "Lutalyse" (Dinoprost-original) which is 10mg IM (1-2ml/horse)
SYNTHETIC is "Estrumate" (cloprostenol) 250ug IM (0.5-1ml/horse) ( ← smaller amt bc synth more powerful!!)
What are side effects if you give too much PGF2α?Sweating
Colic signs
ABORTION in pregnant mares & humans

Ovulation Induction

Question Answer
What are the 3 drugs avail for ovulation induction?(1) hCG (Human Chorionic Gonadotropin)
(2) GnRH
(3) PGF2α
How does hCG work to cz ovulation induction?LH-like effect → Ovulation
What are the necessary prerequisites for hCG to work to induce ovulation?>/= 35 mm follicle (aka 3.5cm), D2-3 of estrus
Why hCG & not eCG?Bc eCG has a FSH like effect & hHG has an LH like effect
We want to mimic LH
Once you give hCG (under the right conditions, ie 3.5cm follicle & D2-3 of estrus), how long till ovulation?Ovulation w/in 36-48h
3 GnRH products avail for induction of ovulation are?(1) Deslorelin
(2) GnRH agonist
(3) SQ implant (in vulva for ease of removal “ovuplant”) or aqueous solution (available overseas)
Once you give GnRH, how long until you expect ovulation?Ovulation w/in 48h
Where do we put the SQ implant for GnRH...& why?Vulvar we can find it easily again
Why do you not want to leave GnRH in for too long?Prolonged interestrus intervals due to downregulation of FSH/LH axis THEREFORE remove implant!!! (Basically switches off the whole cycle)
How does PGF2α cz induction of ovulation?Mechanical contraction of smooth muscle – ie. Capsule around ovary → cz’s ovulation

Suppression of Estrus

Question Answer
What are 2 reasons WHY you'd want to suppress estrus?(1) Competition horses
(2) Riding horses
Permanent sterilization can be used as a way to suppress estrus...implications?Risks? Practicality, economics
2 examples of Reversible Pharmacological ways of suppressing estrus?(1) Daily P4 (Altrenogest)
(2) GnRH agonists (Deslorelin)
Is immunocontraception reversible?Yes
Reversible immunocontraception → what are the 2 ways you can do this?(1) pZP vaccine (Porcine Zona Pellucida)
(2) Anti-GnRH vaccines
pZP vaccine (Porcine Zona Pellucida) end result is that is does what, but doesnt do what?Works as contraception, but DOESNT affect the estrus cycle (feral horse populations where there is establish Hierarchy)
How does anti-GnRH vaccines affect the horses? Where is it usu used?Suppresses reproductive Fxn + behaviour. Feral horses & deer populations currently (potential for abuse? Would affect all animals)