Proceedings of the 5th International Symposium on EQUINE ...

Equine Embryo TransferWHEN DO EQUINE EMBRYOS ENTER THE UTERINECAVITY: AN ATTEMPT TO ANSWER ?I. Battut, A. Grandchamp des Raux, J. L. Nicaise, F. Fieni, D. Tainturier andJ. F. BruyasDepartment <strong>of</strong> Reproduction, Veterinary School, B.P. 40 706, 44307 Nantes Cedex 03, FranceA previous study (Battut et al. 1997) has suggestedthat horse embryos enter <strong>the</strong> uterine cavitybetween 144–156 h after ovulation.Variability indevelopment stage was considerable betweenembryos recovered at <strong>the</strong> same age: from 117–417cells at 156 h and 272–2217 cells at 168 h(Colchen et al. 2000). The purpose <strong>of</strong> <strong>the</strong> presentstudy was: 1) to determine more precisely <strong>the</strong>timing <strong>of</strong> embryonic transport between 144–156 hafter ovulation, if necessary using successiveuterine flushings at 3 or 6 h interval on <strong>the</strong> samemare; and 2) to evaluate homogeneity indevelopment stage among embryos recovered at<strong>the</strong> same age.MATERIALAND METHODSSeventeen mares (9 Trotter, 2 Thoroughbred and 6Pony) were used as embryo donors, between 30thJune and 3rd September. The onset <strong>of</strong> oestrus wasdetected by daily teasing with a stallion, folliculargrowth was <strong>the</strong>n checked by daily ultrasoundexamination. When a growing follicle reached 33mm, ovulation was induced alternatively by one ivinjection <strong>of</strong> 2,500 iu human ChorionicGonadotrophin (hCG), or 4 iv injections <strong>of</strong> 20 µgbuserelin at 12 h intervals. Artificial inseminationwas performed 24 h after <strong>the</strong> first injection, withpooled fresh semen from 2 stallions. Ovulationwas checked hourly by ultrasound examinationsstarting 32 h after injection, until ovulation, oruntil 48 h. Embryo collection was performed byuterine flushing, <strong>the</strong> moment being chosen atrandom; ei<strong>the</strong>r 144, 147 or 150 h after ovulation.When no embryo was obtained, some collectionattempts were repeated 3 or 6 h later (see Fig 1).After recovery, embryos were measured underan inverted microscope, fixed in 2%glutaraldehyde, embedded in Epon 812, sectioned(1 µm) and stained with Toluidin blue forhistological analysis (Bruyas et al. 1993).RESULTSRecovery ratesForty five first collection attempts, 28 second and7 third collection attempts were performed.Induction <strong>of</strong>ovulationA. I.Ovulation144 hEmbryo collection:1st2nd150 h 6 h1st 2nd147 h 3 h1st 2nd 2nd 3rd3 h 3 h 6 hOestrusHourlyDay 6 Day 6.25Day 6.5Fig 1: Experimental protocol.66