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

Havemeyer Foundation Monograph Series No. 3TABLE 1: Effect <strong>of</strong> cryopreservation on embryo grade, size and percent live cellsGrade Diameter (µm) % live cell †Post 20 h Post- 20 hInitial thaw culture S.E. Initial thaw culture S.ETreatmentSlow-cooled 1.4 2.6 2.9 0.2 257 21823811.1 74*Vitrified OPS 1.4 2.9 3.1 0.1 232 184 176 9.9 51Vitrified cryoloop 1.3 2.6 3.3 0.2 211 184 196 11.4 48*Three embryos in <strong>the</strong> slow-cooled treatment group were killed and lost during staining and are not included† sd ± 37liquid nitrogen until thawing in a 4-well dish at37°C. The lid and loop was removed from <strong>the</strong>cryovial under liquid nitrogen. The loopcontaining <strong>the</strong> embryo was sequentially placedinto wells, containing 840 µl H-SOF plus 420 ml<strong>of</strong> H-SOF supplemented with 1 M sucrose for 2.5min, 840 µl H-SOF plus 210 ml <strong>of</strong> H-SOFsupplemented with 1 M sucrose for 3 min, and 840ml H-SOF for 5 min. After thawing, embryos werecultured for 20 h in SOFaa in <strong>the</strong> presence <strong>of</strong> 6%CO 2 , 5% O 2 , 89% N 2 at 38.5°C.Embryos were graded and measured prefreeze,post thaw, and after 20 h <strong>of</strong> culture.Embryos were <strong>the</strong>n stained with propidium iodideand Hoechst 3342 to determine <strong>the</strong> proportion <strong>of</strong>live cells. Embryos were washed in a 100 µldroplet <strong>of</strong> H-SOF under oil and placed in stainingsolution containing H-SOF supplemented with 8mg/ml BSA with 10 µg/ml PI and Hoechst 33342.Embryos were placed into a 100 µl droplet <strong>of</strong>staining solution at 38.5°C for 15 min under foil.After staining embryos were washed twice in H-SOF and mounted on a slide in an 11 µl drop <strong>of</strong> H-SOF, covered with a cover-slip, which mounds onfour drops <strong>of</strong> a paraffin oil/vaseline mixture.Fluorescence was observed with a Nikon EclipseE800 narrowband microscope (Filter FITC,TRITC and DAPI) with a 20X/0.75 objective(Nikon); nuclei and dead cells <strong>of</strong> embryosfluoresce with bright blue and red colour,respectively, and percent live cells were estimated.It was not possible to count <strong>the</strong> cells, due to <strong>the</strong>large numbers <strong>of</strong> cells per embryo. Three differentpeople independently estimated <strong>the</strong> percent livecells and <strong>the</strong> average <strong>of</strong> <strong>the</strong>se numbers were taken.Results were evaluated by analyses <strong>of</strong>variance. There were no significant differences(P>0.1) in grade or size <strong>of</strong> embryos prior tocryopreservation. Upon thawing, an equalproportion <strong>of</strong> embryos fractured in <strong>the</strong> slowcooled,OPS and cryoloop procedure resulting in12.5% (1/8), 18% (2/11) and 12.5% (1/8) fracturedembryos.Because <strong>the</strong> fractured embryos in <strong>the</strong> slowcooledmethod appeared viable <strong>the</strong>y were includedin <strong>the</strong> results. Embryos that survivedcryopreservation were stained, and ranged indiameter from 140–320 µm after 20 h <strong>of</strong> culture.There were no significant differences (P>0.1) inembryo grade or viability post-thaw amongcryopreservation treatments. Embryo grade andviability as assessed by staining were correlatedr =-0.66 (P0.1) as measured bypercent live cells and morphological grades. Inconclusion vitrification procedures with OPS orcryoloop were similarly effective forcryopreservation <strong>of</strong> small equine embryos. Theseresults are in agreement with those obtained ino<strong>the</strong>r species including bovine (Vajta et al. 1998)and hamsters (Lane et al. 1999). Fur<strong>the</strong>r, bothvitrification methods produced results which weresimilar to o<strong>the</strong>r studies where morphological gradepost-thaw and subsequent transfers wereperformed. In those studies embryos graded 1 or1.5 prior to cryopreservation were determined tograde 2.4 on average and result in 50 to 53%pregnancy rates, respectively (Slade et al. 1985;Squires et al. 1989). It is likely, <strong>the</strong>refore, that<strong>the</strong>se techniques will eventually supercede <strong>the</strong>55