When in vitro-produced one-cell embryos (6 h after IVF) were transferred to oviducts of the recipient animals and then flushed 5 days after transfer, the recovered blastocysts had more than 100 nuclei. However, when the embryos were cultured in vitro, development was delayed (about 1 day), and nuclear number in the blastocysts was decreased, present data). Moreover, it was difficult to see the inner cell mass in in vitro-produced blastocysts. These results indicate that poor developmental ability of pig embryos produced in vitro is partially due to suboptimal culture conditions. The present results also indicate that abnormal embryonic division begins with the first cell cycle. One of the anomalies is embryonic fragmentation, which was shown here to account for 24% of 2-cell, 63% of 3-cell, 37% of 4-cell, and 59% of 5- to 8-cell-stage embryos. Most fragmented embryos at the 2- to 4-cell stages had one blas-tomere that did not have a nucleus. Cheap Diskus Advair
However, because such fragmentation occurs at the first and second cell cycles, it may significantly affect subsequent embryo development by reducing both rate of blastocyst formation and total cell number in blastocysts. By contrast, no fragmentation was observed in in vivo-derived embryos. The examination of microfilament distribution indicates that differences are present between in vitro-produced and in vivo-derived embryos, and these differences may be one of the reasons for the low developmental rate of embryos produced in vitro.