hormones used in horse:--by: dr. dhiren bhoi
DESCRIPTION
Hormones Used in Horse:--by: Dr. Dhiren BhoiTRANSCRIPT
The use of exogenous hormones to control estrus
in horses.
Dr. Dhiren B. BhoiM.V.Sc., (Gynaecology)
Learning Objectives
• Reasons why we use hormones for equine reproduction
• Accelerating the transition period
• Initiate ovulation
• Manipulate luteolysis
• Overall schedule exogenous hormones
• Which are best?
Reasons to Establish Controlled Cycles(Pre-determined Schedule)
• The physiologic breeding season: April to Late Summer• Use in absence of a teasing stallion
– Unavailable stallion, difficult to detect heat
• Predicted stallion collection, shipping times• Shorten stays at a breeding farm • Cooled semen shorter life• Decreased handling/efforts, optimize fertility, early foals
for performance• COST/PROFIT$$$
Unique Species• Seasonally polyestrus (long day)
• Ovarian Physiology: Ovulation occurs at a single spot,• “Ovulation Fossa”
• Unlike other farms species, most mares have only one follicular wave – Proestrus phase is the shortest of all farm species
Estrous cycle 21d
Estrus duration 7d
Onset of estrus to ovulation 5d
LH surge to ovulation 2d
Senger, 2003.
Transition Period
• Period of cessation of seasonal anestrus leading to the breeding season
• Presence of multiple small non-ovulatory follicles
• Applications only speed up period; not eliminate– Lighting– GnRH– Progestins– Progestins + Estrogen– eFSH
Transition Period
[# Follicles]
[Follice Size]
[FSH]
[LH]
Donadeu, Ginther, 2002a.
Accelerating the Transition Period*Use a lighting system
Initiates transition period (10-12 wks earlier) FSH levels rise 2 months before the breeding season Caution: Absence of FSH&LH are necessary to trigger initiation
of transition period
Using Progestins (P4-like Hormones)
Suppress GnRH secretion- allows a rebound of LH secretion after the P4 tx is stopped
Mares must be well into transition period to respond (22mm)
Decreases prolonged estrus and anovulation
Complications with Progestins
•(Typically) only one follicular wave
•After the last tx of P4, size of dominant follicle could be small or large
Synchronization dependent on development of follicle
•Spontaneous ovulations during luteal phase
Good info less relevant for the assignment
Progestins
• May also be used to:
– Suppress heat in show mares– Prolong diestrus period to accommodate
stallion collection schedule
Inducing Ovulation
• Why do we need to control time of ovulation?
• Touch on different approaches – don’t need too much detail
Inducing Ovulation
*hCG (Human Chorionic Gonadotropin)
• Large glycoprotein hormone produced by the human placenta
• LH-like: binds to equine LH receptors in ovary for LH peak
• More effective and safer late in transitional period (antibodies)
• Low cost and high clinical effectiveness
Inducing OvulationGnRH Synthetic Agonist
”Ovuplant” implant or new injectable form
• Stimulate release of LH and FSH for ovulation• Ovuplant is placed under the skin
• Use when hCG antibodies are present or a history of hCG
failure
Both hCG and GnRH achieve an ovulation within 48 hours on a 30-45mm follicle-(on ~90% of all mares)
Inducing OvulationeFSH Bioniche (Equine Pituitary Extract)
• Contains LH and FSH
• Stimulate follicular development and advance ovulation in:
– Transitional (shorten period), acyclic & superovulate cycling mares
• Give 5-7days after last ovulationGive for 3-5 days (or until follicles are >35mm)
give hCG / GnRH 36h after last eFSH to induce ovulation
• Limited availability, expensive
PGF2a
• IM Injection
• Luteolysis= binding of PGF2a to the CL during diestrus period
• Since luteal phase of cycle is short, effective PGF2a shot must be given when CL is at least day 6 of luteal phase for luteolysis to occur
• Given during the single follicular wave= regression of the CL– Synchronize cycles (for breeding or embryo transfer)
– Shortens up the luteal phase: sooner ovulation• Ovulation times can still vary significantly
• Immediate increase in LH and FSH and decrease P4
• Side effectsGood info less relevant for the assignment
PGF2a
Prostaglandin Failure (may need a 2nd tx):
• 25-30% of all mares can may exhibit 2 follicular waves– Luteolysis will occur, but large follicles in the ovaries don’t respond
• Follicle present during diestrus is almost mature, onset of estrus is rapid and ovulation is not observed– Masks the original CL lysis: gives impression that PG tx has failed– PG may be strong enough to cause an LH surge leading to ovulation
before luteolysis has occurred
Should always ultrasound to determine true
follicle size for best results
Bringing it all Bringing it all
together…together…
Brief explanation of synchronization protocols as they pertain to the mares unique physiology would be adequate
Control of estrus is the basis of predictable control of ovulation.
PGF2α PGF2α (hCG)hCG
Day 1 6 14 18 20 22
estrus
PGF2a Luteolysis of small CLhCG Ovulate any remaining large follicles 2nd PGF2a Luteolysis of new CL (may speed up luteal phase)
estrus ~3-4d later2nd hCG LH surge to induce ovulation 48hours later (>30mm)
Breed: At ovulation or within 48-72 hours before (time of hCG shot) Dependent on breeding method or shipment timing
Breed
Use this method in conjunction with ultrasound to determine follicle sizeUse as an alternative to progestin treatment when prolonging of the luteal phase is not desired or mare is out of transition period
Novak, 2007
PGF2α Progesterone hCGovulation
Day 1 12 16 18 21
Day 1 8 12 14 16
estrus
Breed
Novak, 2007
•P4 : Given for no more than 15 days •Mare must have some follicular activity (20mm)ie, Lighting system•Removal will initiate GnRH to stimulate LH release
•PGF2a: Given on last day of P4 tx•Luteolysis of remaining CL’s•Mares will come into heat ~3-4 days later
•hCG: LH surge to induce ovulation 48hours later (>30mm)Breed: At ovulation or within 48-72 hours before (time
of hCG shot) Use this method after a period of light stimulation for adequate follicular development to shorten the transition period and calm gonadotropin secretion
for a period when the cycle timing (breeding) needs to be controlled
Suggested for insemination of mares when more than one dose is available:
•Daily examinations during estrus (any time)•Day 0 Day of 35 to 40 mm follicle detection•Administer hCG or deslorelin at approximately 4:00 PM•Day 1 Inseminate a single dose of frozen semen at 4:00 PM (24 hrs post-injection).•Day 2 Inseminate a second dose of frozen semen at 8:00 AM (40 hours post-injection).•Day 3 Examine to confirm ovulation & inseminate 3rd dose if the mare has not ovulated @8AM
www.selectbreeders.com
Selection of a specific agent may be based on:
• Cost
• Efficacy
• Time of year
• Age of the mare
• Follicle size
• Previous use or success
• Clinician preference.
Touch on these – don’t need too much details
• Lofstedt R. 2004. Rational uses of hormones in broodmares. Professor of Theriogenology Atlantic Vetereinary College.
• Lofstedt. R. 2003. The use of progesterone & estradiol in broodmares.
• Donadeu, F.X., Ginther, O.J., 2002a. Follicular waves and circulating concentrations of gonadotrophins, inhibin and oestradiol during the anovulatory season in mares. Reproduction 124, 875–885.
• McCue, P.M., et al. 2006. Comparison of Compounded Deslorelin and hCG for Induction of Ovulation in Mares. Elsevier www.sciencedirect.com. Theriogenology 68.
• McCue, P.M., et al. 2007. eFSH in clinical equine practice. Elsevier www.sciencedirect.com. Theriogenology 68:429–433
• Management of Mares for Frozen Semen Insemination. www.selectbreeders.com• Douglas RH, Ginther OJ. Effect of prostaglandin F2alpha on length of diestrus in
mares.Prostaglandins. 1972 Oct;2(4):265-8. No abstract available. PubMed - indexed for MEDLINE
• http://www.utextension.utk.edu/publications/animals/EquineFacts/TNH1004.pdf– Good summary Factsheet (modern equine Breeding Factsheet)
• Senger P.L. 2003. Pathways to pregnancy and Partuition Second Revised Edition. Pullman, WA: Current Conceptions Inc. Ch8
• Donadeu F.X., Watson E.D. 2006. Seasonal changes in ovarian activity: Lessons learnt from the horse. Animal Reproduction Science. Elsevier 100: 225-242
• McCue P.M., et al. 2007. Comparison of Compounded Deslorelin and hCG for Induction of Ovulation in Mares. Journal of Eqine Veterinary Science. Pg 58-9.
• Crowell-Davis S.L. 2007. Sexual behavior of mares. Hormones and Behavior. www.elsevier.com 52:12-17.