the horse report Vol. 4, No. 2

a publication of theE^quine Research Laboratory,

School ofVeterinaryMedicine,University ofCalifornia, Davis

John P. Hughes, D.V.M., Director

Twin Pregnancies—A Brighter PictureTwin pregnancies are one of

the most common causes ofabortion or early embryonicdeath in normal mares. As aresult, twin conceptions poten¬tially cost the breeding industrymillions of dollars each yearbecause of lost pregnancies.Although veterinarians are ableto reduce the risk of twin preg¬nancies by careful rectalpalpation and manipulation ofbreeding, twinning is still re¬corded in the general stud bookas occurring in 1 to 5% of allpregnancies.Unrecorded and un¬detected abortions of twin andsingle fetuses account foranother 10% loss of potentiallive foals. Placental in¬flammation and disease aremajor causes of infertility andtwin conceptions are thought tocause 35% of all placental-related infertility.To date, most attempts to save

one fetus from twin conceptionshave unfortunatelyyielded disap¬pointing results for both breederand veterinarian. Dr. DavidPascoe, a graduate student withDr. Hughes in the DepartmentofReproduction, recentlycompleted a four-year projectsupported by the Oak TreeRacing Association designed toinvestigate the methods ofproducing one normal foal fromtwin pregnancies.The objective ofDr. Pascoe s

study was to develop a suitable,practical method of removingone embryo from an establishedtwin pregnancy and to maintainthe integrity of the secondembryo, producing one live foal.

Over the 4-year period, twodifferent methods for removingone embryo were utilized: (1) em¬bryonic vesicle rupture ("crush¬ing"), and (2) surgery.The mare's natural defense

mechanisms present some prob¬lems with the success of thesetwo methods. The utems reacts

naturally to infection, irritation,physical manipulation, surgicalprocedures and/or removal of anembryo by releasing potent hor¬mones called prosta^andins.The sudden release of prosta¬glandins triggers the utems toreject the remaining fetus. Toprevent this reaction. Dr. Pascoeexperimented with a variety ofnew steroidal antiinflammatorydmgs (NSAIDs) which werebelieved to suppress thisrejection response. The studydid indeed show that adminis¬tration of single doses ofNSAIDs

Ultrasound scan (sonogram) ojoneof the vesicles ofa 14-day twinpregnancy (actual size). At thisstage, the embryo is not visible tothe naked eye. The vesicle whichholds the tiny embryo (black circu¬lar area) measures an average of11/2 cm. A successful "crush" inthe case of twins can be peiformedat this time.

inhibited release of prosta¬glandins with no measurableside effects.

Diagnostic ultrasound allowsthe veterinarian to detect thepresence of one or two embryosas early as 12 to 14 days of gesta¬tion. During early gestation (12to 30 days), the release of prosta¬glandin is minimal in mostmares and an embryonic vesiclecan be deftly and carefullymptured without creating therejection response. This 12 to 30day period is the mostappropriate time to perform a"crush". Dr. Pascoe ^sorecommends "If a mare is partic¬ularly difficult to palpate,NSAIDs administered before the

crushing procedure minimizethe release of the hormone,giving the remaining fetus a

continued on page 4

Sonogram ofone vesicle oJa 52-day twin pregnancy (actual size).Note the embryo and umbilicalcord (white areas within the darkcircular vesicle). At this stage, theconceptus measures approximately7 cm and one twin can be success¬fully removed using the surgicalprocedure.

The Horse Report, Vol. 4 No. 2

CURRENT RESEARCH

"Investigating the contribution tofetlock and coffin joint functionprovided by the superficial digitalflexor tendon, deep digital flexortendon, and suspensory ligamentof the equine forelimb", Drs. PeterPryor and Dennis Meagher, Depart¬ment ofSurgery (Project funding$3,185)Movement of the equine foreleg is

being studied with the uSe of highspeed cinematography. Informationobtaiined from filming movinghorses is entered into a computerand analyzed using biomechanicaltechniques with the aim of gaininga better understanding of normaland abnormal gaits. The effects ofsome of the corrective surgicaltechniques used in foals with flex¬ing deformities will also be betterunderstood. Dr. KeithWilliams, abiomechanist with the PhysicalEducation Department at UCD, ishelping apply techniques ofmotionanalysis used on human athletes tohorses.

"Continuing investigations into theetiopathogenesis of osteochondro¬sis in horses". Dr. John Pascoe,Department of Surgery, Drs. SusanStover and Roy Pool, DepartmentofPathology, Dr. David Pascoe, De¬partment of Reproduction (Projectfunding $4,084)This project is designed to study

the role of heredity in osteo¬chondrosis (OCD), a conditionwhich occurs in man and in a var¬

iety of domestic animals. OCD is anabnormal development of theeartilage-bone junction in a jointwhich often results in chroniclameness. Siblings from the mat-ings of affected stallions and maresare being examined by clinical andradiographic means from birth tomaturity to evaluate OCD signs.Utilizing embryo cleavage andembryo transfer methods, a largenumber of offspring are being pro¬duced for study, giving a greatersample size.

"The bioavailability and pharma¬cokinetics of orally administeredchloraphenicol in equine neo¬nates", Drs. W. DavidWilson andPeter Adamson, Department ofMedicine, and Dr. DesmondBaggot, Department ofPharmacol¬ogy and Toxicology (Project fund¬ing $2,698)The major objective of this

research is to evaluate the absorp¬tion, distribution and eliminationcharacteristics of chloraphenicol fol¬lowing oral administration of thisantibiotic drug to newborn foals.This will increase our understand¬ing of the maturation of these phys¬iological processes in the foal andpermit better recommendations tobe made regarding chloraphenicoldosage during the critical neonatalperiod. Past studies have shownthat differences are evident betweenindividual foals of different ages andbetween required dosages. Toprovide the best protection againstneonatal infection, it is important toestablish dosage guidelines for spe¬cific ages of foals.

"Diagnostic Specificity ofQuantita¬tive and Qualitative Immunoelec-trophoretic Analysis ofSerum andCerebrospinal Fluid and IgG inEquine Neurologic Disease", Dr.Robert Higgins, Department ofPathology; Dr. Sue Bailey, Depart¬ment ofSurgery; and Dr. JohnMadigan, Department ofMedicine(Project funding $2,158)Currently, the diagnosis of dis¬

eases affecting the brain and spinalcord in the horse is extremely diffi¬cult. This project is designed todevelop a more specific test forbrain and spinal cord disease basedon analysis of certain substances inthe cerebrospinal fluid and blood. Ithas been shown that traumatic,degenerative, inflammatory andneoplastic diseases each producehighly charaeteristic changes in thecerebrospinal fluid and blood whichcan be measured. The techniquebeing developed is relatively simpleand inexpensive and will hopefullyprovide a more rapid and preciseclinical diagnosis resulting in morespecific treatment and accurateprognosis.

(continued from previous issue)

"Endocrinology ofPregnancy inMares and Donke3rs CarryingChimaeric Foals", Dr. RobertPashen, Department ofReproduc¬tion (Project funding $4,000)Early stage embiyos contaiining 2-

8 cells are being surgically flushedfrom the oviducts ofmares anddonkeys. Individual cells from theseembryos are then separated bymicromanipulation and are puttogether to form new "horse-donkey" chimaeras. These horse-donkey embryos exhibit some of theunique characteristics of each spe¬cies and this phenomena is beingused to highlight important eventsof pregnancy. In particular, hor¬mone profiles are being comparedbetween normal and chimaericpregnancies in an attempt to pin¬point reasons for early embryonicloss.

WELSH PONYASSOCIATIONOF CALIFORNIA PRESENTSCONTRIBUTION FOR EQUINEHEALTH RESEARCH

In July Mrs. Roy Straden, awell-known riding and horse-training instructor in the Sacra¬mento area, represented theWelsh Pony Breeders & Exhibi¬tors Association ofCalifornia inpresenting Dr. John Hugheswith a generous donation of$1,200. The Welsh Pony Associa¬tion was originally organized topromoteWelsh Ponies and tostandardize breeding. The Cali¬fornia group recently voted todisband and to lend their timeand support to the variousCounty Fairs and the State Fair.The members also voted to con¬

tribute their proceeds to theEquine Research Laboratory tobe used to fund importantequine health research. In ex¬pressing his gratitude to Mrs.Straden and the CaliforniaWelsh Pony Associationmembers. Dr. Hughes affirmedthat "The ERL's objective is topromote research dealingwiththe health and well-being ofhorses and donations such asthis mean a great deal to thecontinuation of our researchprograms."

The Horse Report, Vol. 4 No. 2

NewHormoneAssayDevelopedH.Lormone assays are becomingmore and more useful to the vet¬erinarian for determining appro¬priate treatment of various typesof endocrine disorders. In thehorse, the determination ofhormone levels produced by theovaries or testicles yield impor¬tant information regardingseveral reproductive problems.One example is the condition

characterized by a persistentluteal phase in the mare, when acorpus luteum does not regressat the normal time in a nonpreg¬nant mare, thereby preventingthe mare from returning toestrus and interferingwith herbreeding potential. In this case,progesterone levels aremeasured in the blood and, ifindicated, prostaglandin treat¬ment is administered to induce

regression of the corpus luteum,thereby allowing the mare toreturn to estrus. Another exam¬

ple involves the detection ofpregnancy and in association,an assessment of fetal wellbeing. Estrogen levels are mea¬sured in pregnant mares to eval¬uate the presence of a live, viablefetus. If the fetus dies, estrogenlevels immediately decline. Thus,the assay is able to provide clini¬cians with critical informationregarding the status of the fetus.In the male, hormone assays

are used to detect levels of testos¬terone to diagnose cryptor¬chidism, a condition wheremales have retained one or bothtesticles in the abdominal cavity.High levels of testosterone indi¬cate cryptorchidism. The resultsof the hormone assay allow theclinician to differentiate ciyp-torchid males from males whichhave been castrated. This cangive the surgeon assurance as tothe necessity of an operation if atesticle(s) is determined to bepresent or can spare the animalfrom unnecessary surgery if theanimal is shown to be castrate.

Recently, Coralie Monroe andDr. George Stabenfeldt in theEndocrinology Laboratory of theDepartment ofReproductionhave developed a new type of

hormone assay called enzymeimmunoassay. The assayinvolves the use of enzymeagents rather radioisotopes aswere used in the previouslystandard radioimmunoassaytest. The radioimmunoassay hasinherent radiation hazards withthe storage, use and disposal ofthe radioisotopes and is alsoexpensive as it requires special¬ized equipment. The enzymeimmunoassay, which utilizesinstrumentation that measuresoptical density, has other advan¬tages to radioimmunoassay withshorter turnaround time

(quicker results to clients) andbecause of the simplicity of theassay, important money-savingpotential.These two researchers have

perfected the new enzymeimmunoassay assay system forprogesterone and are adaptingthe system for estrogen, testos¬terone, follicle stimulating hor¬mone, and luteinizing hormone.While the Endocrinology Labhas sensitive equipment whichcan very accurately measure thelevel of hormones present in theblood, it is anticipated thatfurther adaptation of this uni¬que technique will allow the testto be read visually by trainedtechnical staff.While determina¬tions performed in the labora¬tory involve instrumentmeasure¬ment of optical density, theassay can be read visuallybecause changes in optical den¬sity are caused by a change inthe test medium from appearingcolorless to turning green. It ispossible visually, for example, todeterminewhether or not an ani¬mal has a corpus luteum by eval¬uating the change in the testmedium.With further refinement of the

new enzyme immunoassay, it ispossible that in the future it willbe available for utilization in thepractitioner's office. This wouldbe an important tool for veteri¬narians and horse breeders inmanaging various reproductivedisorders.

Jj;

THANKS, CINDEE!This is Cindee Pascoe's last

issue as co-editor ofTHEHORSE REPORT as she recentlymoved to Queensland, Australiawith her husband. Dr. DavidPascoe. Cindee has made a sig¬nificant contribution to theERL, both as awriter for thisnewsletter and in her capacityas administrative assistant tothe director. For the last three

years, Cindee has authored arti¬cles on the various equineresearch investigations andworked diligently on all aspectsof the publication of this news¬letter to bring to our readersfirst-hand reports of innovativeresearch efforts which result in

improved equine health care. Asadministrative assistant, sheworked closelywith me to coordi¬nate the flurry of activities atERL, promoting interest andsupport for our programs.We wish Cindeee the best of

luck in her adventures andwould like to take this oppor¬tunity to thank her for her dedi¬cation and hard work on behalfof the Equine ResearchLaboratoiy.

John P. Hughes, Director

THE HORSE REPORT

CO-WRITERS/EDITORS:Cindee Pascoe & Cherie Frost

Contributions may be made payable to:REGENTS, LINIVERSITY OF CALIFOR¬NIA. Please include your name andaddress and specify that your donationis for the EQUINE RESEARCHLABORATORY.

Please send contributions to Dr. John P.

Hughes, Director, Equine ResearchLaboratoiy, School ofVeterinaiy Medi¬cine, University of California, Davis, CA95616

(Telephone: 916—752-6433)® The Regents of the University ofCali¬fornia, October 1985

The Horse Report, Vol. 4 No. 2

CONTRIBUTORSCatherine & C.J. SchiappaSallyAnn TylerJanet Hughes EUisVem & Gladys RyanGerald BachecklCherie CooperWilliam BoggessShawn Jaffee Horse TrainingRobert & Catherine LongHarry & Mary Ellen MarkJames & Norma BlatzEllen BlattenbergRobert & Paula HamiltonJane Lee MolnarJames C. Gaines, DVMShaulaWatsonTA. FarreUDoris & Tex JohnsonJohn & Virginia KraftGary MurraySheldon & Theodora JudsonSherrill O'NeillRichard & Betty FlemingThe Hatch RanchRobert & Lise Thomsen JonesHobby Horse ArabiansRonald DeanChristine Fluor

PhyUis Pa3meLouis TroutBert & Joyce HarrisJames & Betty CooleyMinola & Charles FarleyWalker PorterAM. & Thena MimlerJean & Leon MiemikDonald & Helen Stoy

DONORSHalfQuarter Horse Registry ofAmerica

Dorothy P. Barrett

John & Karen JoynerAJ. TorloneDiablo Arabian HorseAssociationRobert & Marilyn HansenRalph & Barbara LopesLomaWelchTom & Mary PageJerry Black, DVMJohn C. Harris

Penelope BradyJack Robbins, VMDC.D. & J.D. McConvilleJohn & Gloria FluorNorma SpearsMrs. John SeekerCharles & Libby FeltnerOrange County Dental SocietyRancho JurisHansen & Hansen, Inc.Mr. & Mrs. Glen Battles

SPONSORSJames A. Rose, DVMSidney L. Port

BENEFACTORSWelsh Poney Breeders &ExhibitorsAssociation ofCalifornia

California Horsemen'sBenevolent& Protective AssociationWomen's Auxiliciry

International Arabian HorseAssociation

Monterey County Horsemen'sAssociation

Francis CostelloThe Leonard Andrews FamilyTrust

TWINS(continuedfrom page 1)

better chance to survive." Usingthis procedure on twin fetusesat 12 to 30 days resulted in asurvival rate for remainingfetuses of 95%, an extraordi¬narily high success rate.When attempting surgical re¬

moval of one fetus, it was foundthat fragility of the placentareduced the chances for success¬ful results when the concep-tuses were younger than 50days gestation. Using the surgi¬cal procedure, a 72% survivalrate of the remaining fetuseswas obtained for fetuses over 50days old and when the pregnan¬cies occurred in sepairate hornsof the uterus. This procedurewas unsuccessful when twinswere conceived in the same ute¬rine horn. Further investigationof the management of twinsconceived in the same uterinehorn is currently underway.The results of this study indi¬

cate that gestational age and theadministration of prosta-glandin-inhibitory drugs areprime factors when choosingmethods ofmanaging twinpregnancies. Most twin preg¬nancies can be successfullymanaged when appropriatemethods are carefully applied.These methods should result ina significant decrease in the per¬centage of loss resulting fromtwin conceptions.

THE HORSE REPORT

E)quine Research LaboratorySchool of Veterinary MedicineUniversity of California, DavisDavis, CA 95616

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