Mare oestrus cycle flashcards
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Describe the equine oestrus cycle?
Mares are seasonally polyoestrus, long day breeders. Cyclicity is triggered by long day lengths
What is the transition period?
Transition from seasonal anoestrus to oestrous. Takes about 45 days. Increased photoperiod triggers GnRH secretion, increased FSH secretion & initiation of follicular development. Little LH secreted, so ovulation doesn't occur for ~ 3.7 follicular waves. Eventually normal follicle develops, LH gene activated, LH secreted, ovulation! Transition over
What are the phases of equine oestrous cycle?
2 phases: Follicular phase (oestrus), dominated by oestrogen, receptive to stallion, variable length (~6.5 days). Luteal phase (dioestrus), dominated by progesterone, not receptive to stallion, length reliably 14-15 days.
What changes do the mare's reproductive organs undergo during oestrus/dioestrus?
Dioestrus: uterus toned, oestrus: uterus flaccid
List (don't describe) the different ways of controlling the oestrus cycle
Shorten CL lifespan, oestrus suppression, oestrus synchronisation, ovulation induction, transition manipulation
Describe the method used to shorten CL lifespan (short-cycle) in mares including drugs, dosages, and timing
Use prostaglandins to shorten luteal phase: Dinoprost (Lutalyse) or Cloprostenol (Estrumate). Only works if given 5-6 days after previous ovulation. Standard (traditional) dose was 10mg IM, now 0.5mg IM for 2 consecutive days (no side effects) - 100% ovulation. Oestrus 3-5 days, ovulate 6.8 days.
How is oxytocin used to suppress oestrus?
Give IM BID for 7 days, during days 7-14 of dioestrus, down regulates oxytocin receptors in endometrium, prolongs luteal phase.
Which progestins can be used for oestrus suppression?
Progesterone or Altrenogest (Regu-mate)
Describe progesterone protocol for oestrus suppression
Progesterone in oil (painful, may abscess at injection site), 150-300mg IM daily. Progesterone in microspheres is slow-release formulation, 7 day duration of action. Induces artificial luteal phase.
Describe Altrenogest (regu-mate) protocol for oestrus suppression
Progestin, give orally, can mix with feed (wear gloves!). Oestrus suppression within 3 days, 60-90 days treatment. Injectable available, 12 or 30 day formulation. Induces artificial luteal phase.
Glass ball protocol for oestrus suppression
40% effective, can be spontaneously expelled, mimics a conceptus. Exact mechanism unknown.
How do GnRH vaccines work to suppress oestrus?
Improvac or Equity - stimulates anti-GnRH antibodies, immunotherapy, act like a vaccine, causes temporary "immune anoestrus". Give 2 doses 4 weeks apart, suppression within 4 weeks, duration ~ 23 weeks.
Permanent oestrus suppression?
Ovarioectomy - flank incision or through vagina.
Oestrus synchronisation by prostaglandin?
Works but doesn't give very tight control, not suitable for embryo transfer
Oestrus synch using Altrenogest?
Progestin, effectiveness depends on timing of treatment. 7/10 ovulated when treated during oestrus. Does not effectively suppress follicular development. Ovulation 7-12 days after end of treatment.
Which oestrus synch protocol is best for embryo transfer?
Progesterone & Estradiol, IM for 10 days. Estradiol causes follicular atresia, P4 causes artificial luteal phase, give PGF at the end. Mild signs of oestrus 24hr after tx but reject stallion. Oestrus within 8 days following treatment, ovulation within 12-13 days post tx. Also available in microspheres (long acting).
How do you induce ovulation?
Use Chorulon (hCG) or Deslorelin (Ovuplant - GnRH analogue) given when follicle >30-35mm. hCG can induce antibody production if given >1 per breeding season. 70-85% ovulation with 24 - 48hrs. Deslorelin 90% ovulation within 48hrs, with no antibodies.
Best technique for using Deslorelin?
Implant in vulval mucosa when follicle >35mm, remove 2 days later - otherwise increases interovulatory period. Using PGF with Deslorelin increases interovulatory period still further
Other ovulation induction techniques?
Injectable deslorelin, reLH
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