RELATIONSHIP BETWEEN THE MATURATIONAL STATE OF OOCYTES AT THE TIME OFINSEMINATION AND SEX-RATIO OF SUBSEQUENT EARLY BOVINE EMBRYOS

The effect of maturational state of bovine oocytes at the time of inse mination on early embryo development and the sex ratio of developing e mbryos was evaluated. Early maturing oocytes were inseminated either i mmediately after the first polar body extrusion or insemination was de layed for 8 h. Most of the zygotes completed the first embryonic cell cycle and reached the 2-cell stage by 35 h after insemination regardle ss of the time of insemination. Delaying insemination enhanced the pro portion of cleaving zygotes and significantly improved their developme nt to the 8-cell stage. At the same time delaying insemination produce d significantly higher proportions of male embryos. Cleavage and devel opment to 8-cell stage was significantly impaired when oocytes were in seminated immediately after polar body formation. Sex ratio in these e mbryos did not differ from 1. These results suggest that oocytes' deve lopmental ability as well as capability to process X and Y-bearing spe rmatozoa may be acquired at specific times during maturation. (C) 1997 by Elsevier Science Inc.