SUPEROVULATION: The Future is Now Patrick M. McCue DVM ...

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SUPEROVULATION: The Future is Now Patrick M. McCue DVM ...

SUPEROVULATION: The Future is NowPatrick M. McCueDVM, PhD, Diplomate American College of TheriogenologistsStimulating mares to have multipleovulations has been an elusive goal in theequine breeding industry for many years. Incontrast, superovulation is routinelyperformed to increase the efficiency ofembryo transfer in cows. Attempts to usehormones successful in inducing multipleovulations in cows, such as folliclestimulating hormone purified from pigpituitary glands (pFSH) and a hormoneproduced by the equine placenta (equinechorionic gonadotropin or eCG) have metwith little or no success in mares. Theability to stimulate multiple follicles todevelop and ovulate would have immediatepractical application in an embryo transferprogram.A single egg or oocyte is released from eachfollicle that ovulates. The egg is transporteddown the oviduct where fertilization mayoccur. Mares that ovulate one follicle havea 40 to 60% chance of becoming pregnanton any given cycle, depending on the typeand quality of semen used and thereproductive health of the mare. Mares thatovulate multiple follicles have a greaterprobability of becoming pregnant, ordonating an embryo, than mares that ovulatea single follicle.Horse owners, breeding managers andveterinarians involved in embryo transferhave traditionally been limited to attempts tocollect one embryo per estrous cycle.However, a pharmaceutical company(Bioniche Animal Health USA, Inc.) hasrecently made available a purified equinefollicle stimulating hormone (eFSH). Thehormone is extracted from horse pituitaryglands and purified using techniques similarto those used in purifying porcine FSH. Acontrolled clinical trial performed in 2002documented that administration of eFSH tocycling mares stimulated multiple folliclesto develop. Inducing ovulation of thestimulated follicles was most efficient usinghuman chorionic gonadotropin (hCG).Mares treated with 12 mg of eFSH followedby hCG ovulated an average of 3.4 folliclesper cycle. Untreated control mares ovulatedan average of 1.1 follicles per cycle.Timing is critical for successful use of eFSHto induce superovulation in mares. The goalof hormone treatment is to stimulatecontinued development of a group offollicles in one wave. A control mechanismexists in mares to limit the number offollicles that develop to the largepreovulatory size. Basically, a wave offollicles starts to develop simultaneously.One follicle soon emerges as the larger ordominant follicle of that particular wave.The dominant follicle produces hormonesthat limit or suppress the development of thesmaller follicles in the wave. The dominantfollicle continues to develop and eventually1


ovulates, while the remainder of thefollicles regress and are permanently lost.Administration of eFSH twice beginning 5or 6 days after ovulation, followed byprostaglandins one day later to eliminate thecorpus luteum, will result in continueddevelopment of multiple follicles infollicular wave. Administration of hCG isrequired to induce a synchronized ovulationof most or all of the large follicles.Embryo collection should be performed 7 or8 days after ovulation of the first detectedovulation. Previous research studies havenoted that embryo collection successincreases as the number of ovulationsincrease in mares. This is especially true foryoung reproductively healthy horses. Oldermares may have a decreased response tosuperovulatory hormones and embryocollection success may be further limited ifthe uterine environment is compromised. Ingeneral, however, superovulation shouldincrease the efficiency of embryo transfer inmares.Clinical uses for eFSH in addition tosuperovulation include advancing the firstovulation of the year in transitional maresand enhancing pregnancy rates in maresbred to subfertile stallions. Researchperformed in the spring of 2003demonstrated that administration of eFSH tomares in the spring transition period resultedin ovulation after approximately 6 to 8 daysof treatment. Consequently, eFSH may bean effective management technique to getmares bred early in the season that are slowto respond to an artificial photoperiod orhave not maintained under lights at all.Additional research in the use of eFSH toimprove pregnancy rates is ongoing.Multiple embryos collected from asuperovulated mareEquine follicle stimulating hormone(eFSH) preparation2

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