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Surgically obtained early sheep embryos collected at morula, blastocyst, expanded blastocyst or hatching/ hatched blastocyst developmental stages were subjected to vitrification. The experiment was carried out by the traditional vitrification method, employing 0.25 ml insemination straws as carriers of embryos. The vitrification medium (VM) based on a modified phosphate-buffered solution (PB1) containing 3.0 g/L bovine serum albumin consisted of 1,2-propanediol, glycerol and sucrose (2.72 M, 1.36 M and 1.0 M - respectively). Embryos (each stage separately) were loaded into straws after 7-10 min of saturation in an equilibration solution (without sucrose). After 1 min period of saturation in VM embryos were plunged into liquid nitrogen. After warming, embryos were cultured in vitro and/or were surgically transferred to a surrogate mother for survival examination. Of 71 embryos tested, only 13 (18.3%) revealed development in vitro. The highest survival rate was observed in the most advanced group of embryos. Of 10 hatching/hatched embryos 6 (60%) survived (reexpanded). Three lambs were born after the transfer of 3 embryos from this group.
The aim of this study was determining influence of some factors on pregnancy results in recipient heifers of fresh embryos. The analysis was carried out on 1641 animals (1847 embryo transfer interventions of an average age of 16-26 months. The mean pregnancy rate in heifers was 46.4% and was dependent (p<0.001) on which the quality of embryos, kind of medium used to embryo collection, herds from recipients descended, number of interventions on one recipient, stage of embryo development, kind of medium to embryo culture and conservation, horn of uterus and the month. The best results were noted in recipients which received very good than poor quality embryos (60 resp. 26.1%). There was a big difference in pregnancy results between recipients coming from different herds (23 resp. 60%). When heifers were used as recipients two or more times the pregnancy results were lower than in heifers used only once (47.1 resp. 43.6% and 19.2%). A significant influence on pregnancy results was also the kind of medium used for the cultivation of embryos (Dulbeco (Menezo) or Dulbeco (Sigma) - 50.2 or 56.6% resp. OCM (Imperial - 26.8%). Likewise results of pregnecies were highest in October (62.2%) and lower in summer months (July 33.3%).
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