[Relation between the quality of cattle embryos after thawing and the pregnancy rate after their transfer].

One hundred and forty-two deep-frozen seven days old bovine embryos were, after thawing and stepwise dilution of cryoprotectant, morphologically evaluated under the stereomicroscope. According to the morphology the embryos were divided into four categories as follows: I--fully expanded blastocysts, II--slightly contracted embryos with a minute part of degenerated cells, III--contracted embryos with some degenerated cells, IV--degenerated embryos and those with heavy-damaged zona pellucida, or its complete loss. After surgical transfer of 37 embryos of class I, 16 (43.2%) recipients were pregnant. Transfer of 53 embryos of class II established 20 (37.7%) pregnancies. After transfer of 28 embryos of class III, 10 (35.7%) recipients were pregnant. Twenty four (17%) embryos included in class IV were excluded from transfer. These results indicate that simple morphological evaluation of embryo after freezing and thawing secures relatively objective selection in field conditions. At least this method enables to reveal morphological changes which are not compatible with further development.