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

Havemeyer Foundation Monograph Series No. 3TABLE 1: Rates <strong>of</strong> successful embryo collection knowing <strong>the</strong> exact age <strong>of</strong> <strong>the</strong> embryoFirst collection attemptSecond and third collection attemptsMoment <strong>of</strong> 144 h 147 h 150 h 147 h 150 h 150 h 156 h 156 hcollection (after 144) (after 144) (after 147) (after 150) (after 144(h after ovulation) and 147)Successful 2/16 3/14 5/15 0/2 1/9 0/9 0/80/7collections (16%) (21%) (33%) (11%)No. <strong>of</strong> embryos 2 4 a 7 b 1Twin embryos were recovered in 1 a or 2 b cases (double ovulations were synchronous)TABLE 2: Morphology <strong>of</strong> embryos recovered 144, 147 or 150 h after ovulationMoment <strong>of</strong> recovery 144 h 147 h 150 h(h after ovulation)No. <strong>of</strong> embryos n = 2 n = 4 n = 8Diameter (µm):mean + sd (range) 186 + 21 163 + 11 166 + 9.8(171-201) (146-168) (153-183)Cell number: 407 + 227( n = 2) 440 (n = 1) 317 + 60 (n = 4)mean + sd (range) (247-568) (274-403)% inner cell mass 37 + 9 29 35 + 7% mitosis 5.6 + 0.7 5.2 5.1 + 3For <strong>the</strong> first collection attempts, rates <strong>of</strong> succesdid not significantly differ according to <strong>the</strong>moment <strong>of</strong> collection. Most <strong>of</strong> <strong>the</strong> time, at secondand third collection attempts, <strong>the</strong> cervix wasrelaxed, and embryos have probably been lost,ei<strong>the</strong>r during flushing or in <strong>the</strong> time elapsedbetween 2 successive collections.In contrast with our previous results (Battut etal. 1997), some embryos were recovered from <strong>the</strong>uterus 144 h (exactly 6 days) after ovulation.Recovery rates at 150 h were lower than thatpreviously reported at 156 h: all <strong>the</strong> embryos donot seem to have reached <strong>the</strong> uterus 150 h (exactly6.25 days) after ovulation. These data corroborateprevious results (Colchen et al. 2000), indicatingthat <strong>the</strong> moment <strong>of</strong> arrival <strong>of</strong> equine embryos in<strong>the</strong> uterus after ovulation varies among embryos,within an interval about 12 h. The possible reasonsexplaining this variability are: i) variable delaybetween ovulation and fertilisation, depending onindividual oocytes; ii) maternal factors: noinfluence <strong>of</strong> maternal breed was observed, andprogesteronemia has no influence (Colchen et al.2000); iii) environmental factors (o<strong>the</strong>r thanseason); and iv) embryonic factors: sex; moment<strong>of</strong> PGE 2 secretion; o<strong>the</strong>r individual factors.MorphologyUnder inverted microscope, all <strong>the</strong> embryoslooked like morula or early blastocyst, <strong>the</strong>difference between <strong>the</strong> 2 stages being difficult toevaluate. Diameters and cell numbers arepresented on Table 2. There was no significantdifference according to <strong>the</strong> moment <strong>of</strong> recovery.Only 8 embryos could be subjected tohistological analysis. One was degenerated, 6 wereearly blastocysts, and one was a morula (150 h,168 µm, 313 cells). Fragments <strong>of</strong> capsule werevisible on all <strong>the</strong> embryos, but a continuous andvery thin capsule was observed only around oneembryo (150 h, 153 µm, 279 cells). Cell numbersare presented on Table 2. There was no correlationbetween diameter, cell number, percentage <strong>of</strong>inner cell mass, and percentage <strong>of</strong> mitosis.These results indicate that morphology <strong>of</strong>equine embryos, between Day 6 and Day 6.25,does not depend on <strong>the</strong>ir age in relation toovulation. Hypo<strong>the</strong>sis <strong>of</strong> explanation are:i) variability in <strong>the</strong> interval ovulation-fertilisation;ii) variability in development rate; iii) variability in<strong>the</strong> interval : arrival in <strong>the</strong> uterus - recovery. In <strong>the</strong>uterus, capsule begins to form, and cell number67