-
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
|
|
