The aim of this study was to evaluate the developmental kinetics of cats' blastocysts in connection with their morphology and blastomeres allocation to trophoblast or embryoblast cells. We examined gross blastocyst morphology and the total number of blastomeres together with its allocation to inner cell mass (ICM) or trophectoderm (TE) cells in pre-implantation feline embryos obtained from 6th to 9th day of in vitro culture. From all the investigated embryos, 61.8% developed to early blastocyst, 37.4% to full and 7.6% to hatching blastocyst stage. The total cell number (TCN) varied form 58 cells in early day 6 to 245 in hatching day 8 blastocyst, with the mean 84.9 cells in early, 156.7 in full, and 204.4 in hatching ones. Day 8 blastocyst had the highest number of total cells, together with the highest mean number of ICM regardless of its morphological assessment. Early blastocyst (apart from day 6) had the highest number of arrested cells, while dead cells were the highest in full day 9 blastocyst. More data about the relationship between blastocyst development and morphology would facilitate the selection of optimal blastocysts for further procedures.
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