BREEDING WITH COOLED SEMEN Patrick M. McCue DVM, PhD ...

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BREEDING WITH COOLED SEMEN Patrick M. McCue DVM, PhD ...

BREEDING WITH COOLED SEMENPatrick M. McCueDVM, PhD, Diplomate American College of TheriogenologistsArtificial insemination of mares withcooled-transported semen has become aroutine procedure in the equine breedingindustry. The ability to cool semen makes itfeasible to ship semen from one location toanother, giving mare and stallion ownersmore flexibility in their breeding programs.In this month’s column we will reviewguidelines for optimizing the use of cooledsemen.A test cool is usually recommended prior tothe breeding season to determine whichsemen extender(s) work best to maintainmotility of sperm from an individual stallion.Spermatozoa from most stallions willremain viable for at least 24 to 48 hourswhen cooled to 5 o C. Consequently, it iscommon practice to ship cooled equinesemen by overnight courier to the farm orclinic where the mare is located. Semenfrom some stallions does not tolerate coolingwell and counter-to-counter or same-daydelivery service may be required to obtainpregnancies.In most instances, stallion owners ormanagers collect semen on specificscheduled days and will only ship semenonce for a given mare per estrous cycle.Consequently, mare management must besufficient to accurately predict the optimalday to call for semen and in most cases ahormone treatment is administered to induceovulation at the optimal time.Mares in a shipped semen program must bemonitored closely by palpation andultrasonography. The first examination isgenerally performed on the second or thirdday of heat to determine the size of thelargest follicle. Subsequent examinationsare performed at 1 to 2 day intervals. Semenis generally ordered when a follicle 35 to 40mm in diameter is first detected. Ifcollection and transport procedures goaccording to plan, the cooled semen willarrive the following day and the mare isinseminated.In order to help ensure that ovulation occurswithin 24 to 48 hours after insemination,mares are commonly administered eitherhuman chorionic gonadotropin (hCG) or thegonadotropin releasing hormone agonistdeslorelin. The ovulation-inducing agentcan be given at the time the semen isordered or at the time semen arrives.Administration of either agent will causeovulation in approximately 36 to 42 hours.Consequently, if the hormone is given whensemen is ordered, the interval frominsemination to ovulation will be less than ifthe hormone is administered when semenarrives.1


It must be kept in mind that once hCG ordeslorelin has been given, the mare is on a‘timed schedule’ for ovulation. If the semendoes not arrive when initially anticipated,the mare may ovulate before theinsemination can be performed. In order toavoid that potential complication, anotheroption is to administer hCG or deslorelineither after the stallion owner has confirmedthat the semen has been collected or oncethe shipment has arrived on the farm.are all key factors in the successful use ofcooled-transported semen.Stallion owners may ship either one or twodoses of semen, each initially containingapproximately 1 billion progressively motilespermatozoa (pms) at a concentration of 25to 50 million pms/ml. Once the shipmentarrives, a dose is removed from the shippingcontainer, gently mixed and inseminateddirectly into the mare without pre-warming.It should be standard procedure to warm asmall sample of semen to approximately37 o C and evaluate motility of thespermatozoa after 15 minutes using amicroscope. It is expected that some loss ofmotility will occur during the shipmentprocess. Most stallions that are consideredto be ‘good coolers’ will still have at least40-50 % of the initial sperm motility after 24hours of cooling.If two doses of semen are shipped,several options are available. The seconddose can be inseminated at the same time asthe initial dose, later that day or early on thefollowing day. If the stallion’s semen doesnot cool well, it is of little value to hold thesemen until the next day. In addition, inolder mares the second dose of semen mayremain unused if the uterus becomesinflamed and filled with fluid following theinitial insemination.Careful mare management, accurate andtimely communication and attention to detail2


Shipping containersFed-Ex truck3

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